History of Jewelry

2007-03-05T08:15:00.000-08:00

Jewellery (Jewelry in American spelling) comprises ornamental objects worn by persons, typically made with gems and precious metals. Costume jewellery is made from less valuable materials. However, jewellery can and has been made out of almost every kind of material.

The word is derived from the word "jewel", which was anglicised from the Old French "jouel" in around the 13th century. Further tracing leads back to the Latin word "jocale", meaning plaything.

Some cultures have a practice of keeping large amounts of wealth stored in the form of jewellery.

Jewellery can also be symbolic, as in the case of Jews wearing a Star of David in the form of jewellery, or, as is the case in many Western cultures, married people wearing a wedding ring. Also see what is: Star of David

Jewellery in various forms has been made and worn by both sexes in almost every (if not every) human culture, on every inhabited continent. Personal adornment seems to be a basic human tendency.

Timeline

This is a timeline of Jewelry production from the first uses of metal in history to the Renaissance.

7000 BCE - Uses of copper in Anatolia, Iran and Eastern Europe.
5000 BCE - Uses of copper in Egypt.
4000 BCE - Smelting technology for copper in Egypt and Iran.
3450 BCE - Use of natural zinc/copper alloy in Egypt.
3500 BCE - Gold makes an appearance in Egyptian jewellery.
3000 BCE - Egypt and Iran making simple hammered iron beads
3000 BCE - The Middle East employ semi-mass-production
2000 BCE - First signs of the swaging technique
2600 BCE - Beaded wires began to be used.
2500 BCE - Egyptians using copper/lead alloys.
2500 BCE - True iron production technology in Near East.
2500 BCE - The intentional addition of silver and copper to gold.
2500 BCE - Gold wires are characterized by seam lines that follow a spiral path along the wire.
2000 BCE - Use of patterned punches
1500 BCE - Earplugs and earrings become popular in Egypt.
1400 BCE - Egypt Amarna period, using resin and mud for repoussé backing.
1400 BCE - Deliberate addition of zinc to copper in Canaan.
1400 BCE - Philistines have iron.
1400 BCE - Very copper rich gold alloys popular in Egypt.
1000 BCE - Persian sheet bronze work 0.05mm thick.
1000 BCE - The start of true engraving.
900 BCE - The Greeks have iron.
700 BCE - World's oldest coinage in Lydia.
575 BCE - In Greece, jewellery is still very rare.
500 BCE - Hafted hammers were being used in some parts.
500 BCE - Iron in use in Britain
400 BCE - Greeks using Beeswax for filler in repoussé.
350 BCE - Use of combined punches and dies of bronze.
325 BCE - Animal or human-headed hoop earrings were popular.
300 BCE - Diadems are first seen.
300 BCE - Red Coral popular in Celtic jewellery.
ACE 50 - Start of the Roman period, where addition of silver to gold becomes almost unknown.
ACE 100 - Sulfur fills hollow gold items throughout the Roman Empire.
ACE 150 - Tin rings found in Nubia
ACE 300 - Lead becomes more common in places.
ACE 400 - Pewter jewellery is made.
ACE 400 - A shale die is found in Britain.
ACE 1500 - The Renaissance

Chinese made first use of diamonds

The axes were fashioned from the second-hardest mineral known to science
Stone age craftsmen in China were polishing objects using diamond 2,000 years before anyone else had the same idea, new evidence suggests.

Gold First Used 4000 BCE: Gold is first known to be used in parts of Central and Eastern Europe.

3000 BCE
The Egyptians master the arts of beating gold into leaf and alloying gold with other metals to achieve variations in hardness and color. They also develop the ability to cast gold, using the lost-wax technique still used in today's jewelry industry.
The Sumer civilization of southern Iraq uses gold to create a wide range of jewelry, often using sophisticated and varied styles still worn today.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Jewelry.

History of Jewelry

2006-12-06T10:33:00.000-08:00

Quartz is the most abundant mineral in the Earth's continental crust. It has a hexagonal crystal structure made of trigonal crystallized silica (silicon dioxide, SiO2), with a hardness of 7 on the Mohs scale. Density is 2.65 g/cm³. The typical shape is a six-sided prism that ends in six-sided pyramids, although these are often twinned, distorted, or so massive that only part of the shape is apparent from a mined specimen. Additionally a bed is a common form, particularly for varieties such as amethyst, where the crystals grow up from a matrix and thus only one termination pyramid is present. A quartz geode consists of a hollow rock (usually with an approximately spherical shape) with a core lined with a bed of crystals.

Varieties

Quartz is one of the world's most common crustal minerals and goes by a bewildering array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.

Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. This does not always hold true.

Not all varieties of quartz are naturally occurring. Prasiolite, an olive colored material, is produced by heat treatment. Although citrine occurs naturally, the majority is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its color.

Because natural quartz is so often twinned, much quartz used in industry is synthesized. Large, flawless and untwined crystals are produced in an autoclave via the hydrothermal process: emeralds are also synthesized in this fashion.

Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."

Quartz is a common constituent of granite, sandstone, limestone, and many other igneous, sedimentary, and metamorphic rocks.

Some quartz crystal structures are piezoelectric and are used as oscillators in electronic devices such as quartz clocks and radios.

Lechatelierite is an amorphous silica glass SiO2 which is formed by lightning strikes in quartz sand.

History

The name "quartz" comes from the German "Quarz", which is of Slavic origin.

Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology.

Roman naturalist Pliny the Elder believed quartz to be permanently frozen ice. He supported this idea by saying that quartz is found near glaciers in the Alps and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum.

Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60 degree angle.

Piezoelectricity

Quartz is also a type of piezoelectric crystal that creates electricity through a process called piezoelectricity when mechanical stress is put upon it. One of the earliest uses for a quartz crystal was a phonograph pickup. Today, one of the most ubiquitous piezoelectric uses of quartz is as a crystal oscillator -- in fact these oscillators are often simply called "quartzes".

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Quartz.

Jewelry: Ruby

2006-11-06T10:35:00.000-08:00

Ruby

Ruby is a red gemstone. Rubies can vary from a light pink to a blood red, a variety of the mineral corundum (aluminium oxide). The color is caused mainly by chromium. Its name comes from ruber, Latin for red. Natural rubies are exceptionally rare, but synthetic rubies (sometimes called created ruby) can be manufactured fairly cheaply. Other varieties of gem-quality corundum are called sapphires. It is considered one of the four precious gems, together with the sapphire, the emerald and the diamond.

Rubies are mined in Africa, Asia, Australia, Greenland, Madagascar and North Carolina. They are most often found in Myanmar (Burma), Sri Lanka, Kenya, Madagascar, and Cambodia, but they have also been found in the U.S. states of Montana, North Carolina and South Carolina. The Mogok Valley in Upper Myanmar has produced some of the finest rubies but, in recent years, very few good rubies have been found there. The unique color in Myanmar (Burmese) rubies is described as "pigeon’s blood". They are known in the trade as “Mogok” rubies. In central Myanmar the area of Mong Hsu also produces rubies. The latest ruby deposit to be found in Myanmar is situated in Nam Ya. In 2002 rubies were found in the Waseges River area of Kenya. Sometimes spinels are found along with rubies in the same rocks and are mistaken for rubies. However, fine red spinels may approach the average ruby in value.

Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only diamond is harder.

Ruby gemstones are valued according to size, color, clarity and cut. All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. If there is no silk in the stone, that shows that the stone was heated to a temperature of up to 1800°C (3272ºF) in an oven to give the ruby a better color of red. Usually the rough stone is heated before cutting. About 90% of all rubies today are heated, and rubies which are not heated are considered unusual. Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300ºC (2372ºF) for 20 to 30 minutes. The silk is partially broken and the color is improved. The fracture filling of rubies is also done intentionally, and it is not always disclosed to gem buyers. Glass-filling voids in rubies, without disclosure, is considered an unethical practice.

Records

Although pieces of red corundum can be found weighing many kilograms, they are generally not of sufficient quality to be valuable as gemstones. For this reason, auction prices are the best indicator of a stone's true value, and prices do not necessarily correlate with size. As of 2006, the record price paid at auction for a single stone was $5,860,000 for an unnamed 38.12 carat cabochon-cut ruby.[1] However, other stones with potentially greater value may never have been sold at auction.

Trivia

A synthetic ruby crystal was used to create the first laser.
According to Rebbenu Bachya, the word odem in the verse Exodus 28:17 means "ruby"; it was the stone on the Ephod representing the tribe of Reuben. Modern Hebrew has taken this meaning.
Ruby is also the most commonly named precious stone in the Bible; an example being Proverbs 31: "A virtuous wife is worth more than rubies."
The famous lighted "Red Stars" mounted above Kremlin spires, thought to be giant rubies mined in Siberia, are actually colored glass.
Ruby is the birthstone associated with July.
Ruby is associated with the Sun in vedic astrology.
Ruby symbolizes passionate love.
Although their names bear some similarity, rubies are not related to rubidium, and they don't contain this chemical element. Both names derive from the same Latin word, ruber, meaning red, in reference to the red color of the ruby, and the red resonance line of rubidium vapor, respectively.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Ruby.

Jewelry: Filigree

2006-10-22T11:42:00.000-07:00

fil·i·gree (fĭl'ĭ-grē')

Delicate and intricate ornamental work made from gold, silver, or other fine twisted wire.

An intricate, delicate, or fanciful ornamentation.
A design resembling such ornamentation: filigrees of frosting on a cake.

Filigree (formerly written filigrann or filigrane) is a jewel work of a delicate kind made with twisted threads usually of gold and silver.

The word, which is usually derived from the Latin filum, thread, and granum, grain, is not found in Ducange, and is indeed of modern origin. According to Prof. Skeat it is derived from the Spanish filigrana, from "filar", to spin, and grano, the grain or principal fiber of the material.

Though filigree has become a special branch of jewel work in modern times it was anciently part of the ordinary work of the jeweler. Signor A. Castellani states, in his "Memoir on the Jewelry of the Ancients" (1861), that all the jewelry of the Etruscans and Greeks (other than that intended for the grave, and therefore of an unsubstantial character) was made by soldering together and so building up the gold rather than by chiseling or engraving the material.

The art may be said to consist in curling, twisting and plaiting fine pliable threads of metal, and uniting them at their points of contact with each other, and with the ground, by means of gold or silver solder and borax, by the help of the blowpipe. Small grains or beads of the same metals are often set in the eyes of volutes, on the junctions, or at intervals at which they will set off the wire-work effectively. The more delicate work is generally protected by framework of stouter wire. Brooches, Star of David, earrings and other personal ornaments of modern filigree are generally surrounded and subdivided by bands of square or

flat metal, giving consistency to the filling up, which would not other-wise keep its proper shape. Some writers of repute have laid equal stress on the glum and the granuna, and have extended the use of the term filigree to include the granulated work of the ancients, even where the twisted wire-work is entirely wanting. Such a wide application of the term is not approved by current usage, according to which the presence of the twisted threads is the predominant fact.

The Egyptian jewelers employed wire, both to lay down on a background and to plait or otherwise arrange d jour. But, with the exception of chains, it cannot be said that filigree work was much practiced by them. Their strength lay rather in their cloisonne work and their molded ornaments. Many examples, however, remain of round plaited gold chains of fine wire, such as are still made by the filigree workers of India, and known as irichinopoly chains. From some of these are hung smaller chains of finer wire with minute fishes and other pendants fastened to them.

In ornaments derived from Phoenician sites, such as Cyprus and Sardinia, patterns of gold wire are laid down with great delicacy on a gold ground, but the art was advanced to its highest perfection in the Greek and Etruscan filigree of the 6th to the 3rd centuries BC. A number of earrings and other personal ornaments found in central Italy are pre-served in the Louvre and in the British Museum. Almost all of them are made of filigree work. Some earrings are in the form of flowers of geometric design, bordered by one or more rims each made up of minute volutes of gold wire, and this kind of ornament is varied by slight differences in the way of disposing the number or arrangement of the volutes. But the feathers and petals of modern Italian filigree are not seen in these ancient designs. Instances occur, but only rarely, in which filigree devices in wire are self-supporting and not applied to metal plates.

The museum of the Hermitage at Saint Petersburg contains an amazingly rich collection of jewelry from the tombs of the Crimea. Many bracelets and necklaces in that collection are made of twisted wire, some in as many as seven rows of plaiting, with clasps in the shape of heads of animals of beaten work. Others are strings of large beads of gold, decorated with volutes, knots and other patterns of wire soldered over the surfaces. (See the "Antiquites du Bosphore Cimmerien", by Gille, 1854; reissued by S. Reinach, 1892, in which will be found careful engravings of these objects.) In the British Museum a sceptre, probably that of a Greek priestess, is covered with plaited and netted gold wipe, finished with a sort of Corinthian capital and a boss of green glass.

It is probable that in India and various parts of central Asia filigree has been worked from the most remote period without any change in the designs. Whether the Asiatic jewelers were influenced by the Greeks settled on that continent, or merely trained under traditions held in common with them, it is certain that the Indian filigree workers retain the same patterns as those of the ancient Greeks, and work them in the same way, down to the present day. Wandering workmen are given so much gold, coined or rough, which is weighed, heated in a pan of charcoal, beaten into wire, and then worked in the courtyard or verandah of the employer's house according to the designs of the artist, who weighs the complete work on restoring it and is paid at a specified rate for his labor. Very fine grains or beads and spines of gold, scarcely thicker than coarse hair, projecting from plates of gold are methods of ornamentation still used.

Passing to later times we may notice in many collections of medieval jewel work (such as that in the South Kensington Museum) reliquaries, covers for the gospels, etc., made either in Constantinople from the 6th to the 12th centuries, or in monasteries in Europe, in which Byzantine goldsmiths' work was studied and imitated. These objects, besides being enriched with precious stones, polished, but not cut into facets, and with enamel, are often decorated with filigree. Large surfaces of gold are sometimes covered with scrolls of filigree soldered on; and corner pieces of the borders of book covers, or the panels of reliquaries, are not infrequently made up of complicated pieces of plaited work alternating with spaces encrusted with enamel. Byzantine filigree work occasionally has small stones set amongst the curves or knots. Examples of such decoration can be seen in the South Kensington and British Museums.

In the north of Europe the Saxons, Britons and Celts were from an early period skilful in several kinds of goldsmiths' work. Admirable examples of filigree patterns laid down in wire on gold, from Anglo-Saxon tombs, may be seen in the British Museum notably a brooch from Dover, and a sword-hilt from Cumberland.

The Irish filigree work is more thoughtful in design and more varied in pattern than that of any period or country that could be named. Its highest perfection must be placed in the loth and lath centuries. The Royal Irish Academy in Dublin contains a number of reliquaries and personal jewels, of which filigree is the general and most remarkable ornament. The "Tara" brooch has been copied and imitated, and the shape and decoration of it are well known. Instead of fine curls or volutes of gold thread, the Irish filigree is varied by numerous designs bi which one thread 'can be traced through curious knots and complications, which, disposed over large surfaces, balance one another, but always with special varieties and arrangements difficult to trace with the eye. The long thread appears and disappears without breach of continuity, the two ends generally worked into the head and the tail of a serpent or a monster. The reliquary containing the "Bell of Saint Patrick" is covered with knotted work in many varieties. A two-handled chalice, called the "Ardagh cup" found near Limerick in 1868, is ornamented with work of this kind of extraordinary fineness. Twelve plaques on a band round the body of the vase, plaques on each handle and round the foot of the vase have a series of different designs of characteristic patterns, in fine filigree wire work wrought on the front of the repousse ground. (See a paper by the 3rd Earl of Dunraven in Transactions of Royal Irish Academy, xxiv. pt. iii. 1873.)

Much of the medieval jewel work all over Europe down to the 15th century, on reliquaries, crosses, croziers and other ecclesiastical goldsmiths' work, is set off with bosses and borders of filigree. Filigree work in silver was practiced by the Moors of Spain during the middle ages with great skill, and was introduced by them and established all over the Peninsula, whence it was carried to the Spanish colonies in America. The Spanish filigree work of the 17th and 18th centuries is of extraordinary complexity (examples in the Victoria and Albert Museum), and silver filigree jewelry of delicate and artistic design is still made in considerable quantities throughout the country.

The manufacture spread over the Balearic Islands, and among the populations that border the Mediterranean. It is still made all over Italy, and in Malta, Albania, the Ionian Islands and many other parts of Greece. That of the Greeks is sometimes on a large scale, with several thicknesses of wires alternating with larger and smaller bosses and beads, sometimes set with turquoises, etc, and mounted on convex plates, making rich ornamental headpieces, belts and breast ornaments. Filigree silver buttons of wire-work and small bosses are worn by the peasants in most of the countries that produce this kind of jewelry.

Silver filigree brooches and buttons are also made in Denmark, Norway and Sweden. Little chains and pendants are added to much of this northern work.

Some very curious filigree work was brought from Abyssinia after the capture of Magdalaarm-guards, slippers, cups, etc, some of which are now in the South Kensington Museum. They are made of thin plates of silver, over which the wire-work is soldered. The filigree is subdivided by narrow borders of simple pattern, and the intervening spaces are made up of many patterns, some with grains set at intervals.

A few words must be added as to the granulated work which, as stated above, some writers have classed under the term of filigree, although the twisted wires may be altogether wanting. Such decoration consists of minute globules of gold, soldered to form patterns on a metal surface. Its use is rare in Egypt. (See J. de Morgan, Fouilles a Dahchour, 1894-1895, pl. xii.) It occurs in Cyprus at an early period, as for instance on a gold pendant in the British Museum from Enkomi in Cyprus (10th century BC). The pendant is in the form of a pomegranate, and has upon it a pattern of triangles, formed by more than 3000 minute globules separately soldered on. It also occurs on ornaments of the 7th century BC from Camirus in Rhodes. But these globules are large, compared with those which are found on Etruscan jewelry. Signor Castellani, who had made the antique jewelry of the Etruscans and Greeks his special study, with the intention of reproducing the ancient models, found it for a long time impossible to revive this particular process of delicate soldering. He overcame the difficulty at last, by the discovery of a traditional school of craftsmen at St Angelo in Vado, by whose help his well-known reproductions were executed.

For examples of antique' work the student should examine the gold ornament rooms of the British Museum, the Louvre and the collection in the Victoria and Albert Museum. The last contains a large and very varied assortment of modern Italian, Spanish, Greek and other jewelry made for the peasants of various countries. It also possesses interesting examples of the modern work in granulated gold by Castellani and Giuliano. The Celtic work is well represented in the Royal Irish Academy in Dublin.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Filigree.

History of Jewelry: Filigree

Jewelry: Sapphire

2006-09-05T10:41:00.000-07:00

Sapphire

Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. It can be found naturally as gemstones or manufactured in large crystal boules for varied applications, including infrared optical components, watch faces, high-durability windows, and wafers for the deposition of semiconductors such as GaN nanorods.

The corundum group consists of pure aluminium oxide. Trace amounts of other elements such as iron, titanium and chromium give sapphires their blue, yellow, pink, purple, orange or greenish color. Sapphire includes any gemstone quality varieties of the mineral corundum except the fully saturated red variety, which is instead known as ruby.

Natural sapphire

Although blue is considered the normal color for sapphire, it is found in the full range of spectral colors as well as brown, colorless, grey and black. Any sapphire other than blue or fully saturated red (ruby) is considered a fancy color sapphire.

Blue sapphire

Various shades of blue result from titanium and iron inclusions within the aluminium oxide crystal lattice. Some stones are not well saturated and show tones of gray. It is common to bake natural sapphires to improve color. This is usually done by heating the sapphires to temperatures of up to 1800°C for several hours, or by heating in a nitrogen deficient atmosphere oven for 7 days or more. On magnification the silk due to included rutile needles are visible. If the needles are unbroken, then the stone was not heated. If the silk is not visible then the stone was heated adequately. If the silk is partially broken then a process known as low tube heat was used. Low tube heat is the process where the rough stone is heated to 1300 °C for 20 to 30 minutes over charcoal. This takes out any gray or brown in the stone and improves color saturation.

Fancy color sapphire

Purple sapphires are lower in price than blue ones. These stones contain the trace element vanadium and come in a wide variety of shades. Yellow and green sapphires have traces of iron which gives them their color. Pink sapphires have a trace element of chromium and the deeper the color pink the higher the value as long as the color is going toward red of rubies.

Color change sapphire

Color shift sapphires are blue in outdoor light and purple in indoor light. Color changes may also be pink in daylight to greenish in fluorescent light. Some stones shift color well and others only partially, in that some stones go from blue to blue purple. White sapphires usually come out of the ground as light gray or brown and are then heated to make them clear. However in very rare circumstances they will be

Star sapphire

A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism. Star sapphires contain intersecting needle-like inclusions (often the mineral rutile) that cause the appearance of a six-rayed 'star'-shaped pattern when viewed with a single overhead light source. Twelve-ray stars are also found, but are less common.

A "star sapphire" ring with two diamonds on a silver band. The value of a star sapphire depends not only on the carat weight of the stone but also the body color, visibility, and intensity of the star.

Treatments

Some sapphires are heat-treated or otherwise enhanced to improve their appearance and color, though some people object to such practices and prefer natural untreated stones. Treated stones tend to be darker than untreated stones and the treatment process causes changes to the internal structure that are generally easily detected.

Mining

Sapphires are mined from alluvial deposits or from primary underground workings. Historically, most sapphires have been mined in Sri Lanka, Madagascar and Myanmar. Australia leads the world in sapphire production (as of 1987) specifically from basalt derived placer deposits in Queensland and New South Wales. Pakistan, Afghanistan, India, Tanzania and Kenya also produce sapphires. The US state of Montana has produced sapphires from the Yogo Gulch deposit near Helena. Gem grade sapphires and rubies are also found in and around Franklin, North Carolina, USA. Several mines are open to the public.

Synthetic sapphire

Synthetic sapphire crystals can be grown in cylindrical crystal ingots of large size, up to many inches in diameter. As well as gemstone applications there are many other uses:

The first ever laser produced was based on the ruby chromium impurity in sapphire. While this laser has few applications, the Ti-sapphire laser is popular due to the relatively rare ability to tune the laser wavelength in the red-to-near infrared region of the electromagnetic spectrum. It can also be easily mode locked. In these lasers, a synthetically produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create stimulated emission.

Pure sapphire ingots can be sliced into wafers and polished to form transparent crystal slices. Such slices are used as watch faces in high quality watches, as the material's exceptional hardness makes the face almost impossible to scratch. Since sapphire ranks a 9 on the Mohs Scale, owners of such watches should still be careful to avoid exposure to diamond jewelry, and should avoid striking their watches against artificial stone and simulated stone surfaces. Such surfaces often contain materials including silicon carbide, which, like diamond, are harder than sapphire and thus capable of causing scratches (Scheel 2003).

Historical and cultural references

According to Rebbenu Bachya, the word "Sapir" in the verse Exodus 28:20 means "Sapphire" and was the stone on the Ephod representing the tribe of Issachar. However, this is disputed as the sapphire of the Bible was likely lapis lazuli (Texas Natural Science Center, 2006).
Supernatural powers were attributed to gems in India. One way this was manifested was the interdependence between gems and planets. Ruby, associated with the Sun, was the Lord of Gems, for the Sun lorded over all the planets. Blue sapphire is associated with Saturn (Wojtilla, 1973), yellow sapphire with Jupiter.

Sapphire is the birthstone associated with September.
The 45th wedding anniversary is known as the sapphire anniversary.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Sapphire.

The History of Jewelry: Sapphires

Jewelry: Emerald

2006-07-07T12:04:00.000-07:00

Emerald

emerald, the green variety of beryl, of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The emerald was highly esteemed in antiquity; the stones were used for ornaments in early Egypt where some of the first emeralds were mined. The finest emeralds are found in South America in Colombia, where they have been mined for over 400 years. The gem was a favorite in pre-Columbian Mexico and Peru, where it was cut in intricate designs. The treasure taken back to Spain by early explorers included emeralds. Good emeralds are the most highly valued of gem stones. India, Zimbabwe, and Australia are minor sources of the natural stones. Synthetic emeralds are also manufactured in Germany, France, and the United States. The Oriental emerald, a different gem, is the transparent green variety of corundum.

Emerald is regarded as the traditional birthstone for May , as well as the traditional gemstone for the astrological signs of Taurus and Cancer.

According to Rebbenu Bachya, the Hebrew word "Nofech" in Exodus 28:18 means "Emerald", and was the stone on the Ephod representing the tribe of Judah. According to other commentaries, "Nofech" means "garnet", and another stone, the "Bareqet", representing the tribe of Levi, is thought to be emerald.

In some cultures, the emerald is the traditional gift for the 55th wedding anniversary. It is also used as a 20th and 35th wedding anniversary stone.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Emerald.

History of Jewelry: Emerald

Jewelry: Turquoise

2006-07-07T11:10:00.000-07:00

Turquoise

Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminum, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market, some difficult to detect even by experts.

The substance has been known by many names, but the word turquoise was derived around 16th century from the French language either from the word for Turkish (Turquois) or dark-blue stone (pierre turquin).[1] This may have arisen from a misconception: turquoise does not occur in Turkey but was traded at Turkish bazaars to Venetian merchants who brought it to Europe.[1] The color, however, has been employed extensively in the decorative tiles adorning Turkish places of worship and homes for hundreds of years, beginning with the Seljuks, and the association quite possibly has caused the name to take root.

Properties of turquoise

Even the finest of turquoise is fractural, reaching a maximum hardness of just under 6, or slightly more than window glass.[2] Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals and all of its properties are highly variable. Its crystal system is proven to be triclinic via X-ray diffraction testing. With lower hardness comes lower specific gravity (high 2.90, low 2.60) and greater porosity: These properties are dependent on grain size. The luster of turquoise is typically waxy to subvitreous, and transparency is usually opaque, but may be semi translucent in thin sections. Color is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green. The blue is attributed to dichromatic copper while the green may be the result of either iron impurities (replacing aluminum) or dehydration.

The refractive index (as measured by sodium light, 589.3 nm) of turquoise is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a gemological refract meter, owing to the almost invariably polycrystalline nature of turquoise. A reading of 1.61–1.65 (birefringence 0.040, biaxial positive) has been taken from rare single crystals. An absorption spectrum may also be obtained with a hand-held spectroscope, revealing a line at 432 nanometers and a weak band at 460 nanometers (this is best seen with strong reflected light). Under long wave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays.

Turquoise is infusible in all but heated hydrochloric acid. Its streak is a pale bluish white and its fracture is conchoidal, leaving a waxy luster. Despite its low hardness relative to other gems, turquoise takes a good polish. Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining.

Formation

As a secondary mineral, turquoise apparently forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of pre-existing minerals. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminum may derive from feldspar; and the phosphorus from apatite. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides. In the American southwest turquoise is almost invariably associated with the weathering products of copper sulfide deposits in or around potassium feldspar bearing porphyritic intrusives. In some occurrences alunite, potassium aluminum sulfate, is a prominent secondary mineral. Typically turquoise mineralization is restricted to a relatively shallow depth of less than 20 m, although it does occur along deeper fracture zones where secondary solutions have greater penetration or the depth to the water table is greater.

Although the features of turquoise occurrences are consistent with a secondary or supergene origin, some sources refer to a hypogene origin. The hypogene hypothesis, which holds that the aqueous solutions originate at significant depth, from hydrothermal processes. Initially at high temperature, these solutions rise upward to surface layers, interacting with and leaching essential elements from pre-existing minerals in the process. As the solutions cool, turquoise precipitates, lining cavities and fractures within the surrounding rock. This hypogene process is applicable to the original copper sulfide deposition; however, it is difficult to account for the many features of turquoise occurrences by a hypogene process. That said, there are reports of two phase fluid inclusions within turquoise grains that give elevated homogenization temperatures of 90 to 190 oC that require explanation.

Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are exceedingly rare. Typically the form is vein or fracture filling, nodular, or botryoidal in habit. Stalactite forms have been reported. Turquoise may also pseudomorphously replace feldspar, apatite, other minerals, or even fossils. Odontolite is fossil bone or ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate vivianite. Intergrowth with other secondary copper minerals such as chrysocolla is also common.

Occurrence

Massive turquoise in matrix with quartz from Mineral Park, Arizona.Turquoise was among the first gems to be mined, and while many historic sites have been depleted, some are still worked to this day. These are all small-scale, often seasonal operations, owing to the limited scope and remoteness of the deposits. Most are worked by hand with little or no mechanization. However, turquoise is often recovered as a byproduct of large-scale copper mining operations, especially in the United States.

Iran

For at least 2,000 years, the region once known as Persia, has remained the most important source of turquoise, for it is here that fine material is most consistently recovered. This "perfect color" deposit that is blue naturally and turns green when heated because getting dehyrated is restricted to a mine-riddled in Neyshabur,[3][4][5] 2,012-metre mountain peak of Ali-mersai, tens of kilometers far from Mashhad, the capital of Khorasan province, Iran. A weathered and broken trachyte is host to the turquoise, which is found both in situ between layers of limonite and sandstone, and amongst the scree at the mountain's base. These workings, together with those of the Sinai Peninsula, are the oldest known.

Iranian turquoise is often found replacing feldspar. Although it is commonly marred by whitish patches, its color and hardness are considered superior to the production of other localities. Iranian turquoise has been mined and traded abroad for centuries, and was probably the source of the first material to reach Europe.

Sinai

Since at least the First Dynasty (3,000 BCE), and possibly before then, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula, called "Country of Turquoise" by the native Monitu. There are six mines in the region, all on the southwest coast of the peninsula, covering an area of some 650 km². The two most important of these mines, from a historic perspective, are Serabit el-Khadim and Wadi Maghareh, believed to be among the oldest of known mines. The former mine is situated about 4 kilometres from an ancient temple dedicated to Hathor.

The turquoise is found in sandstone that is, or was originally, overlain by basalt. Copper and iron workings are present in the area. Large-scale turquoise mining is not profitable today, but the deposits are sporadically quarried by Bedouin peoples using homemade gunpowder. In the rainy winter months, miners face a risk from flash flooding; even in the dry season, death from the collapse of the haphazardly exploited sandstone mine walls is not unheard of. The color of Sinai material is typically greener than Iranian material, but is thought to be stable and fairly durable. Often referred to as Egyptian turquoise, Sinai material is typically the most translucent, and under magnification its surface structure is revealed to be peppered with dark blue discs not seen in material from other localities.

In proximity to nearby Eilat, Israel, an attractive intergrowth of turquoise, malachite, and chrysocolla is found. This rock is called Eilat stone and is often referred to as Israel's national stone: it is worked by local artisans for sale to tourists.

United States

A selection of Ancestral Puebloan (Anasazi) turquoise and orange argillite inlay pieces from Chaco Canyon (dated ca. 1020–1140 CE) show the typical color range and mottling of American turquoise.
Bisbee turquoise commonly has a hard chocolate brown colored matrix, and is considered some of the finest in the world. The Southwest United States is a significant source of turquoise; Arizona, California (San Bernardino, Imperial, and Inyo counties), Colorado (Conejos, El Paso, Lake, and Saguache counties), New Mexico (Eddy, Grant, Otero, and Santa Fe counties) and Nevada (Clark, Elko, Esmerelda County, Eureka, Lander, Mineral County and Nye counties) are (or were) especially rich. The deposits of California and New Mexico were mined by pre-Columbian Native Americans using stone tools, some local and some from as far away as central Mexico. Cerrillos, New Mexico is thought to be the location of the oldest mines; prior to the 1920s, the state was the country's largest producer; it is more or less exhausted today. Only one mine in California, located at Apache Canyon, operates at a commercial capacity today.

The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size. While quite fine material—rivalling Iranian material in both color and durability—is sometimes found, most American turquoise is of a low grade (called "chalk turquoise"); high iron levels mean greens and yellows predominate, and a typically friable consistency precludes use in jewelry in the turquoise's untreated state. Arizona is currently the most important producer of turquoise by value, with the vivid Bisbee Blue being a good example of the state's natural endowment; much of the Arizona material is recovered as a byproduct of copper mining.

Nevada is the country's other major producer, with more than 120 mines which have yielded significant quantities of turquoise. Unlike elsewhere in the US, most Nevada mines have been worked primarily for their gem turquoise and very little has been recovered as a byproduct of other mining operations. Nevada turquoise is found as nuggets, fracture fillings and in breccias as the cement filling interstices between fragments. Because of the geology of the Nevada deposits, a majority of the material produced is hard and dense, being of sufficient quality that no treatment or enhancement is required. While nearly every county in the state has yielded some turquoise, the chief producers are in Lander and Esmerelda Counties. Most of the turquoise deposits in Nevada occur along a wide belt of tectonic activity that coincides with the state's zone of thrust faulting. It strikes about N15E and extends from the northern part of Elko County, southward down to the California border southwest of Tonopah. Nevada has produced a wide diversity of colors and mixes of different matrix patterns, with turquoise from Nevada coming in various shades of blue, blue-green, and green. Nevada produces some unique shades of bright mint to apple to neon yellow green. Some of this unusually colored turquoise may contain significant zinc and iron, which is the cause of the beautiful bright green to yellow-green shades. Some of the green to green yellow shades may actually be Variscite or Faustite, which are secondary phosphate minerals similar in appearance to turquoise. A significant portion of the Nevada material is also noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix". While a number of the Nevada deposits were first worked by Native Americans, the total Nevada turquoise production since the 1870s has been an estimated at more than 600 tons, including nearly 400 tons from the Carico Lake mine. In spite of increased costs, small scale mining operations continue at a number of turquoise properties in Nevada, including the Godber, Orvil Jack and Carico Lake Mines in Lander County, the Pilot Mountain Mine in Mineral County, and several properties in the Royston and Candelaria areas of Esmerelda County.

Rough nuggets from the McGuinness Mine, Austin; Blue and green cabochons showing spiderweb, Bunker Hill Mine, RoystonIn 1912, the first deposit of distinct, single-crystal turquoise was discovered in Lynch Station, Campbell County, Virginia. The crystals, forming a druse over the mother rock, are very small; 1 mm (0.04 inches) is considered large. Until the 1980s Virginia was widely thought to be the only source of distinct crystals; there are now at least 27 other localities. The specimens are highly valued by collectors.

In an attempt to recoup profits and meet demand, some American turquoise is treated or enhanced to a certain degree. These treatments include innocuous waxing and more controversial procedures, such as dyeing and impregnation (see Treatments). There are however, some American mines which produce materials of high enough quality that no treatment or alterations are required. Any such treatments which have been performed should be disclosed to the buyer on sale of the material.

Other sources

China has been a minor source of turquoise for 3,000 years or more. Gem-quality material, in the form of compact nodules, is found in the fractured, silicified limestone of Yunxian and Zhushan, Hubei province. Additionally, Marco Polo reported turquoise found in present-day Sichuan. Most Chinese material is exported, but a few carvings worked in a manner similar to jade exist. In Tibet, where green turquoise has long been appreciated, gem-quality deposits purportedly exist in the mountains of Derge and Nagari-Khorsum in the east and west of the region respectively. However, the existence of these deposits lacks corroboration.

Other notable localities include: Afghanistan; Australia (Victoria and Queensland); northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.

History of use

Trade in turquoise crafts, such as this freeform pendant dating from 1000–1040 CE, is believed to have brought the Ancestral Puebloans of the Chaco Canyon great wealth. The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of Ancient Egypt, the Aztecs (and possibly other Pre-Columbian Mesoamericans), Persia, Mesopotamia, the Indus Valley, and to some extent in ancient China since at least the Shang Dynasty.[8] Despite being one of the oldest gems, probably first introduced to Europe (through Turkey) with other Silk Road novelties, turquoise did not become important as an ornamental stone in the West until the 14th century, following a decline in the Roman Catholic Church's influence which allowed the use of turquoise in secular Jewelry. It was apparently unknown in India until the Muhgal period, and unknown in Japan until the 18th century. A common belief shared by many of these civilizations held that turquoise possessed certain prophylactic qualities; it was thought to change color with the wearer's health and protect him or her from untoward forces.

The Aztecs inlaid turquoise, together with gold, quartz, malachite, jet, jade, coral, and shells, into provocative (and presumably ceremonial) mosaic objects such as masks (some with a human skull as their base), knives, and shields. Natural resins, bitumen and wax were used to bond the turquoise to the objects' base material; this was usually wood, but bone and shell were also used. Like the Aztecs, the Pueblo, Navajo and Apache tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the archer dead aim. Among these peoples turquoise was used in mosaic inlay, in sculptural works, and was fashioned into toroidal beads and freeform pendants. The Ancestral Puebloans (Anasazi) of the Chaco Canyon and surrounding region are believed to have prospered greatly from their production and trading of turquoise objects. The distinctive silver jewelry produced by the Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from circa 1880 as a result of European influences.

In Persia, turquoise was the de facto national stone for millennia, extensively used to decorate objects (from turbans to bridles), mosques, and other important buildings both inside and out, such as the Medresseh-I Shah Hussein Mosque of Isfahan. The Persian style and use of turquoise was later brought to India following the establishment of the Mughal Empire there, its influence seen in high purity gold Jewelry (together with ruby and diamond) and in such buildings as the Taj Mahal. Persian turquoise was often engraved with devotional words in Arabic script which was then inlaid with gold.

The iconic gold burial mask of Tutankhamun, inlaid with turquoise, lapis lazuli, carnelian and colored glass. Cabochons of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold Jewelry of Tibet and Mongolia, where a greener hue is said to be preferred. Most of the pieces made today, with turquoise usually roughly polished into irregular cabochons set simply in silver, are meant for inexpensive export to Western markets and are probably not accurate representations of the original style.

The Egyptian use of turquoise stretches back as far as the First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from Tutankhamun's tomb, most notably the Pharaoh's iconic burial mask which was liberally inlaid with the stone. It also adorned rings and great sweeping necklaces called pectorals. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a scarab motif, accompanied by carnelian, lapis lazuli, and in later pieces, colored glass. Turquoise, associated with the goddess Hathor, was so liked by the Ancient Egyptians that it became (arguably) the first gemstone to be imitated, the fair semblance created by an artificial glazed ceramic product known as faience. (A similar blue ceramic has been recovered from Bronze Age burial sites in the British Isles.)

The French conducted archaeological excavations of Egypt from the mid-19th century through the early 20th. These excavations, including that of Tutankhamun's tomb, created great public interest in the western world, subsequently influencing Jewelry, architecture, and art of the time. Turquoise, already favored for its pastel shades since c. 1810, was a staple of Egyptian Revival pieces. In contemporary Western use, turquoise is most often encountered cut en cabochon in silver rings, bracelets, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces. Lesser material may be carved into fetishes, such as those crafted by the Zuni. While strong sky blues remain superior in value, mottled green and yellowish material is popular with artisans. In Western culture, turquoise is also the traditional birthstone for those born in the month of December.

Turquoise may have significance in Judeo-Christian scripture: In the Book of Exodus, the construction of a "breastplate of judgment" is described as part of the priestly vestments of Aaron (Exodus 28:15–30). Attached to the ephod, the breastplate was adorned with twelve gemstones set in gold and arranged in four rows, each stone engraved with the name of one of the Twelve Tribes of Israel. Of the four stones in the third row, the first and second have been translated to be turquoise by various scholars; others disagree, however, translating the stones to be jacinth (zircon) and agate respectively.[9] Scholars also disagree as to which tribes each stone is meant to represent.

Imitations

The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product faience. Later glass and enamel were also used, and in modern times more sophisticated ceramics, porcelain, plastics, and various assembled, pressed, bonded, and sintered products (composed of various copper and aluminum compounds) have been developed: examples of the latter include "Viennese turquoise", made from precipitated aluminum phosphate colored by copper oleate; and "neolith", a mixture of bayerite and copper phosphate. Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972 Pierre Gilson introduced one fairly close to a true synthetic (it does differ in chemical composition owing to a binder used, meaning it is best described as a stimulant rather than a synthetic). Gilson turquoise is made in both a uniform color and with black "spiderweb matrix" veining not unlike the natural Nevada material.

Some natural blue to blue-green materials, such as this botryoidal chrysocolla with quartz drusy, are occasionally confused with, or used to imitate turquoise. The most common imitation of turquoise encountered today is dyed howlite and magnesite, both white in their natural states, and the former also having natural (and convincing) black veining similar to that of turquoise. Dyed chalcedony, jasper, and marble is less common, and much less convincing. Other natural materials occasionally confused with or used in lieu of turquoise include: variscite; faustite; chrysocolla (especially when impregnating quartz); lazulite; smithsonite; hemimorphite; wardite; and a fossil bone or tooth called odontolite or "bone turquoise", colored blue naturally by the mineral vivianite. While rarely encountered today, odontolite was once mined in large quantities—specifically for its use as a substitute for turquoise—in southern France.

These fakes are detected by gemologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both color (usually a uniform dark blue) and texture (usually granular or sugary). Glass and plastic will have a much greater translucency, with bubbles or flow lines often visible just below the surface. Staining between grain boundaries may be visible in dyed imitations.

Some destructive tests may, however, be necessary; for example, the application of diluted hydrochloric acid will cause the carbonates odontolite and magnesite to effervesce and howlite to turn green, while a heated probe may give rise to the acrid smell so indicative of plastic. Differences in specific gravity, refractive index, light absorption (as evident in a material's absorption spectrum), and other physical and optical properties are also considered as means of separation. Imitation turquoise is so prevalent that it likely outnumbers real turquoise by a wide margin. Even material used in authentic Native American and Tibetan Jewelry is often fake or, at best, heavily treated.

Treatments

Turquoise is treated to enhance both its color and durability (i.e., increased hardness and decreased porosity). Historically, light waxing and oiling were the first treatments to be used (since ancient times), providing a wetting effect (thereby enhancing the color and luster); this treatment is more or less acceptable by tradition, and because such material is usually of a higher grade to begin with. Conversely, the later development of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass—also producing a wetting effect in addition to improving durability—are rejected by some as too radical an alteration. Plastic and water glass are technologically superior to oil and wax in that the former treatment are far more permanent and stable, and can be applied to material too friable for oil or wax to be of sufficient help; such material is termed "bonded" or "stabilized" turquoise. The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today. The majority of American material is now treated in this manner; although it is a costly process requiring many months to complete, without impregnation most American mining operations would be unprofitable.

Oiled and waxed stones are also prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time. (With some skill, oil and wax treatments can be restored.) Likewise, the use of Prussian blue and other dyes—often in conjunction with bonding treatments—to enhance (that is, make uniform or completely change) color is regarded as fraudulent by purists—especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise. Perhaps the most radical of treatments is "reconstitution", wherein supposedly fragments of fine material too small to be used singly are powdered and then bonded to form a solid mass. Much (if not all) of this "reconstituted" material is likely a complete fabrication (with no natural components), or may have foreign filler material added to it (see Imitations section). Another treatment—the details of which remain undisclosed—is the so-called Zachery process, named after its developer, electrical engineer and turquoise trader James E. Zachery. This process claims to use only medium grade material at a minimum, leaving the turquoise harder and with a better color and luster.

As the finer turquoise is often found as thin seams, it may be glued to a base of stronger foreign material as a means of reinforcement. These are termed doublets and can be very deceptive in certain Jewelry setting styles (such as closed back and bevel settings). Some turquoise is cut with the mother rock serving as a base; these are usually not considered doublets but may have an intrinsic value lower than that of "whole" stones. Doublets, like the aforementioned treatments, are legal provided they are disclosed to the customer before sale.

As is so often with gems, full disclosure is frequently not given; it is therefore left to gemologists to detect these treatments in suspect stones, using a variety of testing methods—some of which are necessarily destructive. For example, the use of a heated probe applied to an inconspicuous spot will reveal oil, wax, or plastic treatment with certainty.

Valuation and care

Richness of color is the chief determiner of value in turquoise; generally speaking, the most desirable is a strong sky to "robin's egg" blue (in reference to the eggs of the American Robin); value decreases with the increase of green hue, lightening of color, and mottling. In Tibet, however, a greener blue is said to be preferred. Whatever the color, turquoise should not be excessively soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolor over time and will not hold up to normal use in Jewelry.

The mother rock or matrix in which turquoise is found can often be seen as splotches or a network of brown or black veins running through the stone in a netted pattern; this veining may add value to the stone if the result is complimentary, but such a result is uncommon. Such material is sometimes described as "spiderweb matrix"; it is most valued in the Southwest United States and Far East, but is not highly appreciated in the Near East where unblemished and vein-free material is ideal (regardless of how complimentary the veining may be). Uniformity of color is desired, and in finished pieces the quality of workmanship is also a factor; this includes the quality of the polish and the symmetry of the stone. Calibrated stones—that is, stones adhering to standard Jewelry setting measurements—may also be more sought after. Like coral and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimeters rather than weight.

Turquoise is treated in many different ways, some more permanent and radical than others. Controversy exists as to whether some of these treatments should be acceptable, but one can be more or less forgiven universally: This is the light waxing or oiling applied to most gem turquoise to improve its color and luster; if the material is of high quality to begin with, very little of the wax or oil is absorbed and the turquoise therefore does not "rely" on this impermanent treatment for its beauty. All other factors being equal, untreated turquoise will always command a higher price. Bonded and "reconstituted" material is worth considerably less.

Being a phosphate mineral, turquoise is inherently fragile and sensitive to solvents; perfume and other cosmetics will attack the finish and may alter the color of turquoise gems, as will skin oils, as will most commercial jewelry cleaning fluids. Prolonged exposure to direct sunlight may also discolor or dehydrate turquoise. Care should therefore be taken when wearing such jewels: cosmetics, including sunscreen and hairspray, should be applied before putting on turquoise Jewelry, and they should not be worn to a beach or other sun-bathed environment. After use, turquoise should be gently cleaned with a soft cloth to avoid a build up of residue, and should be stored in its own box to avoid scratching by harder gems. Also, make sure the box is not airtight, or the turquoise will become ruined.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Turquoise.

History of Jewelry: Turquoise

Jewelry: Diamonds

2006-07-07T09:37:00.000-07:00

Terms

Carat Weight

Clarity

Color

Cut

Diamond is one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light makes it useful for industrial applications and jewelry. The other equally well known allotrope is graphite; but diamonds are specifically renowned as a mineral with superlative physical qualities. They make excellent abrasives because they can only be scratched by other diamonds, which also means they hold a polish extremely well and retain luster. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly 9 billion US$.

The name "diamond" derives from the ancient Greek adamas (αδάμας; "impossible to tame"). They have been treasured as gems since their use as religious icons in India at least 2,500 years ago—and usage in drill bits and engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of improved cutting and polishing techniques, and they are commonly judged by the "four Cs": carat, clarity, color, and cut. Nearly four times the mass of natural diamonds are produced as synthetic diamond each year, though these are typically classified with poor-quality specimens that are suitable only for industrial-grade use.

Most natural diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, Russia, Brazil, and Australia. They are generally mined from volcanic pipes, which are deep in the Earth where the high pressure and temperature enables the formation of the crystals. The mining and distribution of natural diamonds are subjects of frequent controversy—such as with concerns over the sale of conflict diamonds by African paramilitary groups. There are also allegations that the De Beers Group misuses its dominance in the industry to control supply and manipulate price via monopolistic practices.

Crystal structure

Diamonds typically crystallize in the cubic crystal system and consist of tetrahedrally bonded carbon atoms. Lonsdaleite is a polymorph of diamond (and a distinct mineral species) that crystallizes with hexagonal symmetry; it is rarely found in nature, but is characteristic of synthetic diamonds. A cryptocrystalline variety of diamond is called carbonado. A colorless, grey or black diamond with a tiny radial structure is a spherulite.

The tetrahedral arrangement of atoms in a diamond crystal is the source of many of diamond's properties; graphite, another allotrope of carbon, has a rhombohedral crystal structure and as a result shows dramatically different physical characteristics—contrary to diamond, graphite is a very soft, dark grey, opaque mineral.

Hardness

Diamond is the hardest known naturally occurring material, scoring 10 on the relative Mohs scale of mineral hardness and having an absolute hardness value of between 167 and 231 gigapascals in various tests. Diamond's hardness has been known since antiquity, and is the source of its name. However, aggregated diamond nanorods, an allotrope of carbon first synthesized in 2005, are now believed to be even harder than diamond.

Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. It is one of the most known and most useful of more than 3,000 known minerals. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, or use of diamond powder as an abrasive. Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most other diamonds, which are excellent electrical insulators. Industrial-grade diamonds are either unsuitable for use as gems or synthetically produced, which lowers their price and makes their use economically feasible. Industrial applications, especially as drill bits and engraving tools, also date to ancient times.

The hardness of diamonds also contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well, keeping its luster over long periods of time. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in an engagement ring or wedding ring, which are often worn everyday.

Toughness

Unlike hardness, which only denotes resistance to scratching, diamond's toughness is only fair to good. Toughness relates to a material's ability to resist breakage from forceful impact. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamonds cut into certain particular shapes are therefore more prone to breakage than others.

Color

Diamonds occur in a variety of transparent hues — colorless, white, steel, blue, yellow, orange, red, green, pink, brown—or colored black. Diamonds with a detectable hue to them are known as colored diamonds. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice. The most common impurity, nitrogen, causes a yellowish or brownish tinge.

Thermodynamic stability

At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (ΔG = −2.99 kJ / mol). Diamonds will burn at approximately 800 degrees Celsius, providing that enough oxygen is available. This was shown in the late 18th century, and previously described during Roman times. So, despite the popular advertising slogan, diamonds are not forever. However, owing to a very large kinetic energy barrier, diamonds are metastable; under normal conditions, it would take an extremely long time (possibly more than the age of the Universe) for diamond to decay into graphite.

Electromagnetic properties

Optical properties

Diamonds exhibit a high dispersion of visible light. This strong ability to split white light into its component colors is an important aspect of diamond's attraction as a gemstone, giving it impressive prismatic action that results in so-called fire in a well-cut stone. The luster of a diamond, a characterization of how light interacts with the surface of a crystal, is brilliant and is described as adamantine, which simply means diamond-like. This is owed to their high refractive index of 2.417 (at 589.3 nm), which causes total internal reflection to occur. Some diamonds exhibit fluorescence of various colors under long wave ultraviolet light, but generally show bluish-white, yellowish or greenish fluorescence under X-rays. Some diamonds show no fluorescence.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Diamonds.

Sapphires in the United States

2006-06-06T08:00:00.000-07:00

The production of gem-quality sapphires in the United States is not new or recent. In 1865, the first U.S. sapphires were found in the gravels of the Missouri River in Lewis and Clark County, Montana. This was followed by subsequent discoveries on Dry Cottonwood Creek in Deer Lodge County in 1889, on Rock Creek in Granite County in 1892, and in Yogo Gulch in Judith Basin County in 1895. Additionally, small amounts of sapphire are recovered from Quartz Gulch in Granite County, Pole Creek in Madison County, the Missouri River in Chouteau County, and Brown's Gulch in Silver Bow County. Furthermore, corundum crystals, from which star sapphires have been cut, are found in Beaverhead and Madison Counties. Also, in 1895, the first sapphires were produced from the Cowee Valley in Macon County, North Carolina. But until very recently, with the exception of Yogo Gulch material, the commercial gemstone industry has had limited interest in U.S. sapphires.

Montana.--Mining of Yogo Gulch sapphires began within a year of their discovery in 1895 and continued for 39 years. In 1923, the mine was damaged so badly by rain that it could not economically recover. Other attempts have been made to commercially mine the deposit, but to date, all of these attempts have ended in economic failure.

Yogo's are unique among the world's sapphires. They lack the color zoning so prevalent in other sapphires, their uniform "corn-flower blue" color is natural (not the result of heat-treating), and their clarity is uniformly high. These features rank them among the world's finest sapphires. Unfortunately, the rough is both small and flat, wafer-like in shape. The majority of the crystals or pieces of crystals recovered are too small to be cut, most are less than 1 carat and finds of over 2 carats are rare. Reportedly, the largest crystal was a 19 carat stone found in 1910 that was cut into an 8-carat stone. The size of the cut stones greatly restrict the market for Yogo's, they are beautiful, small, very expensive sapphires.

Currently, Yogo sapphires are produced from three sources: Rancor lnc., produces material from the original Yogo Gulch deposit; Vortex Mining produces from a recently discovered extension of the Yogo dike; and material is produced by individuals from privately owned lots in Sapphire Village. The first two producers market only cut stones and finished goods and the third is comprised essentially of hobbyists.

Historically, the amount of sapphires produced from the Missouri River and Rock Creek areas greatly exceeded that from Yogo Gulch. However, the value of the material produced from Yogo, reported to be in excess of $30 million, is significantly greater than that of the combined values of the other areas. This relationship is rapidly changing.

The combination of large volume commercial operations on the Missouri River, and to some extent Rock Creek, plus the advent of successful heat-treating techniques for the material has greatly enhanced the acceptance of these sapphires by the gemstone industry. This enhanced acceptance has resulted in a significant increase in the market for and value of U.S. sapphires. Unconfirmed reports have circulated that a parcel of select 3- to 10-carat material, suitable for heat-treating, was sold for as much as $40,000 per kilogram. A more realistic price for 3- to 10-carat, sorted mine-run material is in the range of $5,000 per kilogram, with many kilograms of mine-run rough selling for $1,000 per kilogram.

The sapphires from the Missouri River gravels in Lewis and Clark County are a mixture of rough and pitted crystals showing well defined faces and completely rounded and smooth-surface highly stream worn pebbles. The majority of the material is pale blue or blue-green, with deep blue stones quite rare. Stones also are found in pastel blue, green, pink, pale red, purple, yellow, and orange. Most of the stones recovered are less than 6.4 millimeters in diameter, but material 6.4 to 12.7 millimeters in diameter are not uncommon. Material greater than 12.7 millimeters in diameter is rare.

Currently there are seven operations on the Missouri River that commercially produce sapphires and/or operate a dig-for-fee area. Not all of these may be active in any one year. It is the author's understanding that one operation, currently inactive, (a self-propelled floating 16-inch suction dredge) is for sale. The mines operate from about the last week of May through the first week of September.

The Rock Creek sapphires are very similar to the sapphires from the Missouri River but differ in the general shape of the crystals. The stones are basically crude hexagonal plates about the same dimension in width and height, with a much higher percentage of the material being well rounded water worn pebbles. There appears to be more of the larger sized (greater than 12.7 millimeters) material. Additionally, it is reported that the Rock Creek material has a greater percentage of stones that can be heat-treated for color enhancement.

During the past several years, there has been only a single producer on Rock Creek. The producer operated both a commercial recovery plant and a fee recovery area. The fee recovery area sold buckets of gravel for washing and also offered, for a predetermined fixed fee, the output of one day's operation of the commercial wash plant. There is work underway which would result in a second, much larger producer, opening an operation on another deposit in the area. If things go as planned, the new operation on Rock Creek would be the largest sapphire producer in Montana.

There are a number of locations between Dillon in Beaverhead County and Ennis in Madison County that produce lavender, grayish-lavender, bluish-gray, and gray hexagonal sapphire crystals that, when cut, produce stones that contain four- or six-ray stars. At least one producer from the Dillon area is currently advertising the availability of this type of material. The remainder of the sapphire deposits in Montana appear to be operated by individual hobbyists.

More should be said about the effects of heat-treating techniques on Montana sapphires, and the variety of fancy colored sapphires available. Not all Montana sapphires are suitable for heat- treating because of variations in chemical composition. Also, the sapphires from the Missouri River respond to heat-treating differently than those from Rock Creek The response to heat-treating can vary also depending upon the method (individual) used to treat the sapphires.

The yield on treatment of Missouri River sapphires is lower than for Rock Creek. It is reported that 20% to 30% of Missouri River sapphires heat-treat from deep, well saturated blue to pale, pale blue. The corresponding treatment rate for Rock Creek material is in the range of 60%. Heat-treating also yields or improves the color of fancy colored sapphires. Bright yellows and oranges are the result of heat-treating, whereas heat-treating improves the color of some pinks by removing colors that can interfere with the desirable pink shades. Montana sapphires can be diffusion treated, but because of their high iron content they are not particularly well suited for this form of enhancement.

North Carolina.--North Carolina is well known for its hobbyist production of sapphire. Sapphire have been produced from the Cowee Valley in Macon County since 1895 when the American Prospecting and Mining Co. systematically mined and washed the gravels of Cowee Creek. Today a number of dig-for-fee operations are located in the Cowee Valley. Each year many people pay to dig or purchase buckets of gravel to wash in hopes of finding a sapphire, garnets, and other gem materials. Many of the dig-for-fee operations have enriched the gravels with gem materials from other locations.

Every year articles appear in magazines and newspapers about large and valuable sapphires found at one or more of the mines in Cowee Valley. No doubt large corundum crystals and pieces of corundum are found each year. By the same token, valuable sapphires may be found, but the number of large valuable gemstones are far less than reported, and the values are generally not as great as reported. During the period when the area was commercially mined, gem material was found that would cut fine quality 3- to 4-carat stones, but the amount of quality gem material available has greatly declined. It is doubtful that North Carolina will ever again boast of commercial sapphire production, or that the commercial gemstone industry will seriously consider the State's sapphire deposits.

Zircon

2006-06-05T11:32:00.000-07:00

Zircon is a mineral belonging to the group of nesosilicates. Its chemical formula is ZrSiO4. Hafnium is almost always present ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal class. The natural color of zircon varies between colorless, yellow-golden, red, brown or green. Colorless specimens that show gem quality are a popular substitute for diamond; these specimens are also known as "Matura diamond" (but note that cubic zirconia is a completely different synthetic mineral with a different chemical composition).

Zircon is a remarkable mineral, if only for its almost ubiquitous presence in the crust of Earth. It is found in igneous rocks (as primary crystallization products), in metamorphic rocks (as recrystallized grains) and in sedimentary rocks (as detrital grains). Large zircon crystals are seldom abundant. Their average size, e.g. in granite rocks, is about 100-300 µm, but they can also grow to sizes of several centimeters, especially in pegmatites.

The pervasive occurrence of zircon has become more important since the discovery of radiometric dating. Zircons contain amounts of uranium and thorium (from 10 ppm up to 5 wt%) and can be dated using modern analytical techniques. Since zircons have the capability to survive geologic processes like erosion, transport, even high-grade metamorphism, they are used as protolith indicators. The oldest minerals found so far are zircons from the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, with an age of 4.404 billion years. This age is interpreted to be the age of crystallization. These zircons are not only the oldest minerals on earth, they also show another interesting feature. Their oxygen isotopic composition has been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth. This is a spectacular interpretation that has been published in top scientific journals but is widely disputed. It is most likely that the oxygen isotopes, and other compositional features (the rare earth elements), simply record hydrothermal alteration. The timing of the alteration is uncertain, but this negates the necessity for ancient liquid-water oceans.

Owing to their uranium and thorium content, some zircons may undergo metamictization. This partially disrupts the crystal structure and explains the highly variable properties of zircon.

Commercially, zircons are mined for the metal zirconium which is used for abrasive and insolating purposes. It is the source of zirconium oxide , one of the most refractory materials known. Crucibles of ZrO are used to fuse platinum at temperatures in excess of 1755 oC. Zirconium metal is used in nuclear reactors due to its neutron absorption properties. Large specimens are appreciated as gemstones, owing to their high refractive index (zicon has a refraction of around 1.95, diamond of around 2.4). The color of zircons that do not have gem quality can be changed by heat treatment. Depending on the amount of heat applied, colorless, blue and golden-yellow zircons can be made.

The name derives from the Arabic word zarqun, meaning vermilion, or perhaps from the Persian zargun, meaning golden-colored. These words are corrupted into "jargoon", a term applied to light-colored zircons. Yellow zircon is called hyacinth, from a word of East Indian origin; in the Middle Ages all yellow stones of East Indian origin were called hyacinth, but today this term is restricted to the yellow zircons.

Zircon is a common accessory mineral and found worldwide. Noted occurrences include: in the Ural Mountains; Trentino, Monte Somma; and Vesuvius, Italy; Arendal, Norway; Sri Lanka, India; Thailand; at the Kimberley mines, Republic of South Africa; Madagascar; and in Canada in Renfrew County, Ontario, and Grenville, Quebec. In the United States: Litchfield, Maine; Chesterfield, Massachusetts; in Essex, Orange, and St. Lawrence Counties, New York; Henderson County, North Carolina; the Pikes Peak district of Colorado; and Llano County, Texas.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Zircon.

History of Jewelry: Zircon

Jewelry: Troy Ounce

2006-05-01T11:38:00.000-07:00

Troy weight is a system of units of mass customarily used for precious metals and gemstones

Troy Ounce: Troy ounce of a fineness of 999.9 parts per 1,000 parts, equal to 31.1034 grams.

History

Troy weight originates from what was called the troy system of mass. Dating back to before the time of William the Conqueror, the name comes from the city of Troyes in France, an important trading city in the Middle Ages.

Units Troy ounce

A troy ounce, the only currently used unit of the system, is 480 grains, somewhat heavier than an avoirdupois ounce (437.5 grains). A grain is exactly 64.798 91 mg, hence one troy ounce is exactly 31.103 476 8 g, about 10 per cent more than the avoirdupois ounce, which is exactly 28.349 523 125 g. The troy ounce is the only ounce used in the pricing of precious metals, such as gold, platinum, and silver, and this is the only remaining use of the troy ounce. In troy weight, there are 12 ounces in a pound, rather than 16 in the more-common avoirdupois system.

Troy pound

A troy pound is 5760 grains (about 373.24 g), while an avoirdupois pound is 7000 grains (about 453.59 g).

1 troy ounce = 31.1034768 grams

Conversions

Unit	Grains	Grams
Pound (12 ounces)	5760	373.241 72
Ounce (20 pennyweights)	480	31.103 477
Pennyweight	24	1.555 173 8
Grain	1	0.064 798 91

Also see	Gold History
	Jewelry History
	Gems Index

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Troy Ounce.

History of Jewelry: Troy Ounce

History of the Star of David

2006-03-28T12:36:00.000-08:00

Star of David

The Star of David is a poplar theme for Jewish Jewelry.

The six points of the Star of David symbolize God's rule over the universe in all six directions: north, south, east, west, up and down.

Originally, the Hebrew name Magen David -- literally "Shield of David" -- poetically referred to God. It acknowledges that our military hero, King David, did not win by his own might, but by the support of the Almighty. This is also alluded to in the third blessing after the Haftorah reading on Shabbat: "Blessed are you God, Shield of David."

The Star of David (Magen David in Hebrew or Mogen Dovid in Ashkenazi Hebrew, Shield of David, Solomon's Seal, or Seal of Solomon) is a generally recognized symbol of Judaism and Jewish identity. Geometrically it is a hexagram. It is also known colloquially as the Jewish Star. With the establishment of the State of Israel the Jewish Star on the flag of Israel has also become a symbol of Israel.

Origin

The shield of David is not mentioned in rabbinic literature. Notably, not a single archeological proof exists as yet concerning the use of this symbol in the Holy Land in ancient times, even after King David. A David's shield has recently been noted on a Jewish tombstone at Taranto, in Southern Italy, which may date as early as the third century of the common era. The earliest Jewish literary source which mentions it, the Eshkol ha-Kofer of the Karaite Judah Hadassi (middle of the 12th century), says, in ch. 242: "Seven names of angels precede the mezuzah: Michael, Gabriel, etc.... Tetragrammaton protect thee! And likewise the sign called 'David's shield' is placed beside the name of each angel." It was, therefore, at this time a sign on amulets.

In magic papyri of antiquity, pentagrams, together with stars and other signs, are frequently found on amulets bearing the Jewish names of God, and used to guard against fever and other diseases. Curiously enough, only the pentacle appears, not the hexagram. In the great magic papyrus at Paris and London there are twenty-two signs side by side, and a circle with twelve signs, but neither a pentacle nor a hexagram. The syncretism of Hellenistic, Jewish, and Coptic influences probably did not, therefore, originate the symbol. It is possible that it was the Kabbalah that derived the symbol from the Templars. Kabbalah makes use of this sign, arranging the Ten Sephiroth, or spheres, in it, and placing it on amulets.

A manuscript Tanakh dated 1307 and belonging to Rabbi Yosef bar Yehuda ben Marvas from Toledo, Spain, was decorated with a Shield of David.

In the synagogues, perhaps, it took the place of the mezuzah, and the name "shield of David" may have been given it in virtue of its presumed protective powers. The hexagram may have been employed originally also as an architectural ornament on synagogues, as it is, for example, on the cathedrals of Brandenburg and Stendal, and on the Marktkirche at Hanover. A pentacle in this form is found on the ancient synagogue at Tell Hum.

In 1354, King of Bohemia Charles IV prescribed for the Jews of Prague a red flag with both David's shield and Solomon's seal, while the red flag with which the Jews met King Matthias of Hungary in the 15th century showed two pentacles with two golden stars (Schwandtner, Scriptores Rerum Hungaricarum, ii. 148). The pentacle, therefore, may also have been used among the Jews. It occurs in a manuscript as early as the year 1073 (facsimile in M. Friedmann, Seder Eliyahu Rabbah ve-Seder Eliyahu Ztṭa, Vienna, 1901).

In 1460, the Jews of Ofen (Budapest, Hungary) received King Mathios Kuruvenus with a red flag on which were two Shields of David and two stars. In the first Hebrew prayer book, printed in Prague in 1512, a large Shield of David appears on the cover. In the colophon is written: "Each man beneath his flag according to the house of their fathers... and he will merit to bestow a bountiful gift on anyone who grasps the Shield of David." In 1592, Mordechai Maizel was allowed to affix "a flag of King David, similar to that located on the Main Synagogue" to his synagogue in Prague. In 1648, the Jews of Prague were again allowed a flag, in acknowledgment of their part in defending the city against the Swedes. On a red background was a yellow Shield of David, in the centre of which was a Swedish star.

Jewish lore links the symbol to the "Seal of Solomon", the magical signet ring used by King Solomon to control demons and spirits. Jewish lore also links the symbol to a magic shield owned by King David that protected him from enemies. Following Jewish emancipation after the French revolution, Jewish communities chose the Star of David to represent themselves, comparable to the cross used by most Christians. The star is found on the flag of Israel.

The shape of the star is an example of the hexagram, a symbol which has significance for other belief systems. The hexagram pre-dates its use by Jews. Its most prevalent usage outside of Judaism was and is the occult.

Another theory about the origin of the shape is that it is simply 2 of the 3 letters in the name David. In its Hebrew spelling, David contains only 3 characters, 2 of which are "D" (or "Dalet", in Hebrew). In ancient times, this letter was written in a form much like a triangle, similar to the greek letter "Delta", with which it shares a sound and the same (4th) position in their respective alphabets, as it does with English. The symbol may have been a simple family crest formed by flipping and juxtaposing the two most prominent letters in the name.

So whether it is a blue star waving proudly on a flag, or a gold star adorning a synagogue's entrance, the Star of David stands as a reminder that for the Jewish people... in God we trust.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Star of David.

Jewelry: Cubic Zirconia

2006-03-28T11:35:00.000-08:00

Cubic Zirconia (or CZ) is zirconium oxide (ZrO2), a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4).

Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. Its main competition as a synthetic gemstone is the more recently cultivated material moissanite.

Technical aspects

Cubic zirconia is, as its name would imply, crystallographically isometric, and as diamond is also isometric, this is an important attribute of a would-be diamond simulant. Synthesized material contains a certain mole percentage (10-15%) of metal oxide stabilizer. During synthesis zirconium oxide would otherwise form monoclinic crystals, as that is its stable form under normal atmospheric conditions. The stabilizer is required for cubic crystal formation; it may be typically either yttrium or calcium oxide, the amount and stabilizer used depending on the many recipes of individual manufacturers. Therefore the physical and optical properties of synthesized CZ vary, all values being ranges.

It is a dense substance, with a specific gravity between 5.6 - 6.0. Cubic zirconia is relatively hard, at about 8.5 on the Mohs scale - nowhere near diamond, but much harder than most natural gems. Its refractive index is high at 2.15 - 2.18 (B-G interval) and its luster is subadamantine. Its dispersion is very high at 0.058 - 0.066, exceeding that of diamond (0.044). Cubic zirconia has no cleavage and exhibits a conchoidal fracture. It is considered brittle.

Under shortwave UV cubic zirconia typically luminesces a yellow, greenish yellow or "beige." Under longwave UV the effect is greatly diminished, with sometimes a whitish glow being seen. Colored stones may show a strong, complex rare earth absorption spectrum.

History

Since 1892 the yellowish, monoclinic mineral baddeleyite had been the only natural form of zirconium oxide known. Being of rare occurrence it had little economic importance.

The extremely high melting point of zirconia (2750°C) posed a hurdle to controlled single-crystal growth, as no existing crucible could hold it in its molten state. However, stabilization of zirconium oxide had been realized early on, with the synthetic product stabilized zirconia introduced in 1930. Although cubic, it was in the form of a polycrystalline ceramic: it was made use of as a refractory material, highly resistant to chemical and thermal (up to 2540°C) attack.

Seven years later, German mineralogists M. V. Stackelberg and K. Chudoba discovered naturally occurring cubic zirconia in the form of microscopic grains included in metamict zircon. Thought to be a byproduct of the metamictization process, the two scientists did not think the mineral important enough to formally name. The discovery was confirmed through x-ray diffraction, proving a natural counterpart to the synthetic product exists.

As with the majority of diamond imitations, the conceptual birth of single-crystal cubic zirconia began in the minds of scientists seeking a new and versatile material for use in lasers and other optical applications. Its evolution would eclipse earlier synthetics, such as synthetic strontium titanate, synthetic rutile, YAG (Yttrium Aluminium Garnet) and GGG (Gadolinium Gallium Garnet).

Some of the earliest research into controlled single-crystal growth of cubic zirconia occurred in 1960s France, much work being done by Y. Roulin and R. Collongues. The technique developed saw molten zirconia contained within itself with crystal growth from the melt: The process was named cold crucible, an allusion to the system of water cooling used. Though promising, these pursuits yielded only small crystals.

Later, Soviet scientists under V. V. Osiko at the Lebedev Physical Institute in Moscow perfected the technique, which was then named skull crucible (an allusion either to the shape of the water-cooled container or to the occasional form of crystals grown). They named the jewel Fianit, but the name was not used outside of the USSR. Their breakthrough was published in 1973, and commercial production began in 1976. By 1980 annual global production had reached 50 million carats (10,000 kg).

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Cubic Zirconia.

History of Jewelry: Cubic Zirconia

Tourmaline

2006-03-28T11:27:00.000-08:00

Tourmaline

The mineral tourmaline is chemically one of the most complicated silicate minerals. It is a complex silicate of aluminum and boron but because of isomorphism replacement (solid solution) its composition varies widely with iron, magnesium and lithium and other elements entering into the combination to a greater or lesser extent.

Tourmaline belongs to the trigonal crystal system and occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section. Interestingly the style of termination at the ends of crystals is asymmetrical, called hemimorphism. Small slender prismatic crystals are common in a fine grained granite called aplite often forming radial daisy like patterns. Tourmaline is distinguished by its three sided prisms, no other common mineral has three sides. Prisms faces often have heavy vertical striations that produce a rounded triangular effect. Tourmaline is rarely perfectly ethereal. An exception were the fine dravite tourmalines of Yinnietharra western Australia. The deposit was discovered in the 1970s but it is now exhausted.

All hemimorphy crystals are piezoelectric and often also pyroelectric. Tourmaline crystals when warmed become positively charged at one end and negatively charged at the other. Due to this effect tourmaline crystals in collections may attract unsightly coatings of dust when displayed under hot spotlights. Tourmalines unusual electrical properties made it famous in the early 18th century. Brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy demand as curios and gems. At the time it was not realized that schorl and tourmaline were the same mineral.

Tourmaline has a wide variety of colors. Usually it is iron rich black to bluish-black to deep brown, magnesium rich varieties are brown to yellow, and lithium rich tourmalines are practically any color of the rainbow, blue, green, red, yellow or pink etc. but most rarely of all it is colorless. Bi-colored and multicolored crystals are relatively common, reflecting variations of fluid chemistry during crystallization. Crystals maybe green at one end and pink at the other or green on the outside and pink inside, this type is called watermelon tourmaline. Some forms of tourmaline are diachronic, in that they appear to change color as when viewed from different directions.

The most common variety of tourmaline is schorl, it was first described by Mathesius in 1524. It may account for 95% or more of all tourmaline in nature. The word tourmaline is corruption of the Ceylonese word turamali meaning stone attracting ash. The meaning of the word schorl is a mystery but it maybe a Scandinavian word.

Tourmaline is found in two main geological occurrences. Igneous rocks, in particular granite and granite pegmatite and in metamorphic rocks such as schist and marble. Schorl and lithium rich tourmalines are usually found in granite and granite pegmatite. Mg rich tourmalines, dravites, are generally restricted to schists and marble. Also, tourmaline is a durable mineral and can be found in minor amounts as grains in sandstone and conglomerate.

Tourmaline is used in jewelry, pressure gauges and specialist microphones. In jewelry, blue indicolite is the most expensive followed by green verdelite and pink rubellite. Ironically the rarest variety, colorless achroite is not appreciated and is the least expensive of the transparent tourmalines.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Tourmaline.

History of Jewelry: Tourmaline

Jewelry: Topaz

2006-03-28T11:09:00.000-08:00

Topaz

This article is about the mineral or gemstone, for other uses see: Topaz (disambiguation).

The mineral topaz is a silicate of aluminium and fluorine with the chemical formula (AlF)2SiO4. It is orthorhombic and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. It has an easy and perfect basal cleavage and so gemstones or other fine specimens should be handled with care to avoid developing cleavage flaws. The fracture is conchoidal to uneven. Topaz has a hardness of 8, a specific gravity of 3.4-3.6, and a vitreous lustre. Pure topaz is transparent but is usually tinted by impurities; typical topaz is wine or straw-yellow. They may also be white, gray, green, blue, or reddish-yellow and transparent or translucent. When heated, yellow topaz often becomes reddish-pink. It can also be irradiated, turning the stone a light and distinctive shade of blue.

Topaz is found associated with the more acid rocks of the granite and rhyolite type and may be found with fluorite and cassiterite. It can be found in the Ural and Ilmen mountains, Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico, and the United States.

The name "topaz" is derived from the Greek topazos, "to seek," which was the name of an island in the Red Sea that was difficult to find and from which a yellow stone (now believed to be a yellowish olivine) was mined in ancient times. In the Middle Ages the name topaz was used to refer to any yellow gemstone, but now the name is only properly applied to the silicate described above.

Topaz is also the birthstone of November.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Topaz.

History of Jewelry: Topaz

Jewelry: Diamonds

2006-03-28T08:28:00.000-08:00

As a gemstone, Diamond's single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.

In terms of it's physical properties, diamond is the ultimate mineral in several ways:

Hardness: Diamond is a perfect "10", defining the top of the hardness scale.
Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.
Thermal Conductivity: Diamond conducts heat better than anything - five times better than the second best element, Silver!
Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)!
Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance!

Opal

2006-03-06T10:24:00.000-08:00

Opal

opal, a mineral consisting of poorly crystalline to amorphous silica, SiO2·nH2O; the water content is quite variable but usually ranges from 3% to 10%. Common opal is usually colorless or white, but it may be gray, brown, yellow, or red; the color is due to fine-grained impurities. Opal is formed at low temperatures from silica-bearing waters and can occur in fissures and cavities of any rock type. Precious, or gem, opal has a rich iridescence and remarkable play of changing colors, usually in red, green, and blue. This is the result of a specific internal structure consisting of regularly packed uniform spheres of amorphous silica a few tenths of a micron in diameter; sphere diameter and refractive index determine the range of colors displayed. The greater part of the world's supply of precious opal comes from the Coober Pedy and Andamooka fields in South Australia. The original source, known in Roman times, was in what is now E Slovakia. Precious opal has also been mined in Honduras, Mexico, and the Virgin Valley in Nevada. Fire opal is a bright red transparent or translucent opal that may or may not show a play of color.

Precious opal

Precious opal shows a variable interplay of internal colours and does have an internal structure. At the micro scale precious opal is composed of hexagonal or cubic closely packed silica spheres some 150 to 300 nm in diameter. These ordered silica spheres produce the internal colors by causing the interference and diffraction of light passing through the microstructure of opal (Klein and Hurlbut, 1985, p. 444). In addition, microfractures may be filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, which is correctly termed play of color. Contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Potch does not show a play of color.

The veins of opal displaying the play of color are often quite thin, and this has given rise to unusual methods of preparing the stone as a gem. An opal doublet is a thin layer of colorful material, backed by a black mineral, such as ironstone, basalt or obsidian. The darker backing emphasizes the play of color, and results in a more attractive display than a lighter potch. Given the texture of opals, they can be quite difficult to polish to a reasonable lustre. The triplet cut backs the colored material with a dark backing, and then has a cap of clear quartz (rock crystal) on top, which takes a high polish, and acts as a protective layer for the comparatively delicate opal.

Opal is symbolic of love, death, and breaking up. In the Medieval Times, the opal stone was given by a male to an unwanted female mate.

Common opal

Besides the gemstone varieties that show a play of color, there are other kinds of common opal such as the milk opal, milky bluish to greenish (which can sometimes be of gemstone quality); resin opal, honey-yellow with a resinous lustre; wood opal, caused by the replacement of the organic material in wood with opal; menilite brown or grey; hyalite, a colorless glass-clear opal sometimes called Muller's Glass; geyserite, (siliceous sinter) deposited around hot springs or geysers; and diatomite or diatomaceous earth, the accumulations of diatom shells or tests.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Opal.

Jewelry: Tazanite

2006-01-25T11:01:00.000-08:00

Tanzanite

Tanzanite is the blue/purple variety of the mineral zoisite discovered in the Meralani Hills of northern Tanzania in 1967, near the city of Arusha. It is a popular and valuable gemstone when cut, although its durability is somewhat lacking. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet, and sage-green depending on crystal orientation. However, most tanzanite is subjected to artificial heat treatment to improve its color: this significantly subdues its trichroism.

The name tanzanite was a trade name coined by Tiffany & Co. shortly after the gem's discovery, an obvious allusion to its country of origin. This was thought necessary in order to make the stone marketable to the public: the name has since stuck as a varietal designation. Tanzanite's present-day popularity as a gemstone is largely thanks to Tiffany's marketing campaigns. The mining of tanzanite nets the Tanzanian government approximately USD $20 million annually, the finished gems later being sold mostly on the US market for sales totaling approx. USD $500 million annually.

In June of 2003, the Tanzanian government introduced legislation banning the export of unprocessed tanzanite to India (like many gemstones, most tanzanite is cut in Japer). The ban has been rationalized as an attempt to spur development of local processing facilities, thereby boosting the economy and recouping profits. This ban will be phased in over the next two years, until which time only stones over 0.5 grams are affected.

This is a grave situation for the city of Japer, as one-third of its annual gem exports are of tanzanite. Some members of the industry fear the ban will set a dangerous precedent, leading Tanzania to ban the export of all raw gem material, including the country's production of tsavorite, diamond and ruby.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Tanzanite.

History of Jewelry: Tanzanite

Israel Diamonds Exports Grow By 6%

2006-01-01T08:37:00.000-08:00

Ramat Gan ----July 5..... Israel net polished diamonds export industry rose 6% from January to June 2005, according to statistics reported by the Israel Ministry of Industry, Trade and Labor's Diamond Controller, Shmuel Mordechai.

Why Buy Diamonds from Israel?

Israel is one of the world’s leading diamond manufacturing and trading centers, selling to numerous markets over the world. Israel sold over $6.3 billion worth of polished diamonds in 2004 for the following main reasons: half of all gem quality diamonds sold around the world are coming from Israel.

Israel is the largest consumer of rough diamonds in the world. Israel produces high quality diamonds, based on expert craftsmanship combined with innovative technology. From lasers to robotics, Israel is at the forefront of technological advances in diamond manufacture.

The Israel Diamond Exchange is the largest in the world, offering the greatest selection of diamonds under one roof. Buying in Israel is safe and convenient – the Diamond Exchange complex is a virtual citadel, where diamonds are traded in complete security. Israeli diamantaires are reliable, flexible and gear themselves to clients’ needs. Israel leads the world diamond industry in innovating new cuts.

Diamond Fats

2005-03-28T08:51:00.000-08:00

Diamond Facts

The largest Diamond ever found:
Cullinan at 3,106 carats.
What is the hardest natural substance on Earth?
The Diamond.
80% of the world's diamonds are not suitable for Jewelry.
Is a Diamond Indestructible?
No. The fact that Diamonds are a hard substance refers to their ability to withstand scratching. But that is different than toughness, which refers to the ability to withstand breaking or cleavage.
How old are most diamonds which are found in nature?
1 billion to 3 billion years, by most accounts.
How do diamonds reach us?
They are formed deep within the Earth's crust, and come to the surface via Volcanoes. Most diamonds are found in Kimberlite, which is volcanic rock.

History of Star of David

2005-03-10T14:00:00.000-08:00

The Shield of David or Magen David in Hebrew, מָגֵן דָּוִד with nikkud or מגן דוד without, pronounced Mahgayn Daveed [ma.'gayn da.'veed] in Modern Hebrew and Mogein Dovid or Mogen Dovid in Ashkenazi Hebrew and Yiddish is a generally recognized symbol of Jewish Community and Judaism. It is named after King David of ancient Israel; and its usage began in the Middle Ages, alongside the more ancient symbol of the menorah.

With the establishment of the State of Israel in 1948 the Star of David on the Flag of Israel has also become a symbol of Israel. In the late 1990's Ethiopia also adopted the Star of David as the Focus of the Flag of Ethiopia, replacing the now infamous Lion of Judah as the focus of the Ethiopian Flag.

As a Jewish symbol

According to some Judaic sources, the Star/Shield of David signifies the number seven: that is, the six points plus the center. The earliest extant Jewish text to mention it is the Eshkol Ha-Kofer by a Karaite named Judah Hadassi, from the 12th century CE:

"Seven names of angels precede the mezuzah: Michael, Gabriel, etc. ... Tetragrammaton protect you! And likewise the sign, called the 'Shield of David', is placed beside the name of each angel."[1]

The number seven has religious significance in Judaism, e.g., the six days of Creation plus the seventh day of rest, the six working days in the week plus Shabbat, the Seven Spirits of God, as well as the Menorah in the ancient Temple, whose seven oil lamps rest on three stems branching from each side of a central pole. And so on. Perhaps, the Star of David came to be used as a standard symbol in synagogues because its organization into 3+3+1 corresponds to the Temple's Menorah, which was the more traditional symbol for Judaism in ancient times.

Some researchers have theorized that the hexagram represents the astrological chart at the time of David's birth or anointment as king. The hexagram is also known as the "King's Star" in astrological circles, and was an important astrological symbol in Zoroastrianism.

The earliest archaeological evidence for the Jewish use of the symbol comes from an inscription attributed to Joshua ben Asayahu in late 7th century BCE Sidon.

"Practical" Kabbalah makes use of this sign, arranging the Ten Sephiroth, or spheres, in it, and placing it on amulets. However, the sign is nowhere to be found in classical kabbalistic texts themselves, such as the Zohar and the like. Therefore, its use as a sefirotic diagram in amulets is more likely a reinterpretation of a preexisting magical symbol. According to G.S. Oegema,

"Isaac Luria provided the Shield of David with a further mystical meaning. In his book "Etz Hachayim" he teaches that the elements of the plate for the Seder evening have to be placed in the order of the hexagram: above the three sefirot "Crown", "Wisdom", and "Insight", below the other seven". [2]

M. Costa wrote that M. Gudemann and other researchers in the 1920s claimed that Isaac Luria influenced the becoming of the Star of David a national Jewish emblem by teaching that the elements of the plate for the Seder evening have to be placed in the order of the hexagram, but Gershom Scholem proved that Isaac Luria talked about parallel triangles one beneath the other and not about the hexagram. [3]

Kabbalistically, the Star/Shield of David symbolizes the six directions of space plus the center, under the influence of the description of space found in the Sefer Yetsira: Up, Down, East, West, South, North, and Center. Congruently, under the influence of the Zohar, it represents the Six Sefirot of the Male (Zeir Anpin) united with the Seventh Sefirot of the Female (Nekuva).

A popular folk etymology has it that the Star of David is literally modeled after the shield of the young Israelite warrior David (later to be King David). In order to save metal, the shield was not made of metal but of leather spanned across the simplest metal frame that would hold the round shield: two interlocking triangles. No reliable historical evidence for this etymology exists.

Shield form

The Shield of David is not mentioned in ancient rabbinic literature. Notably, not a single archaeological proof exists concerning the use of this symbol in the Land of Israel during BCE. Scientists say that it probably was not a widely recognized symbol in the Israel of the Second Temple era. A supposed David's shield however has recently been noted on a Jewish tombstone at Taranto, in Southern Italy, which may date as early as the third century CE. Likewise, a stone bearing the shield from the arch of a 3-4th century synagogue in the Galilee was found. [4]

The earliest Jewish literary source which mentions the "Shield of David" is the Eshkol Ha-Kofer by Judah Hadassi from the middle of the 12th century CE, where seven Shields are used in an amulet for a mezuzah. It appears to have been in use as part of amulets before it was in use in formal Jewish contexts.

A manuscript Tanakh dated 1307 and belonging to Rabbi Yosef bar Yehuda ben Marvas from Toledo, Spain, was decorated with a Shield of David.

In the synagogues, perhaps, it was associated with the mezuzah. Originally, the hexagram may have been employed as an architectural ornament on synagogues, as it is, for example, on the cathedrals of Brandenburg and Stendal, and on the Marktkirche at Hanover. A pentagram in this form is found on the ancient synagogue at Tell Hum.
A page from a 14th century manuscript of the Guide for the Perplexed by Maimonides. The figure seated on the chair with Stars of David is thought to be Aristotle
A page from a 14th century manuscript of the Guide for the Perplexed by Maimonides. The figure seated on the chair with Stars of David is thought to be Aristotle

Shield with stars

In 1354, King of Bohemia Charles IV prescribed for the Jews of Prague a red flag with both David's shield and Solomon's seal, while the red flag with which the Jews met King Matthias of Hungary in the 15th century showed two pentagrams with two golden stars (Schwandtner, Scriptores Rerum Hungaricarum, ii. 148). The pentagram, therefore, may also have been used among the Jews. It occurs in a manuscript as early as the year 1073 (facsimile in M. Friedmann, Seder Eliyahu Rabbah ve-Seder Eliyahu Ztṭa, Vienna, 1901).

In 1460, the Jews of Ofen (Budapest, Hungary) received King Mathios Kuruvenus with a red flag on which were two Shields of David and two stars. In the first Hebrew prayer book, printed in Prague in 1512, a large Shield of David appears on the cover. In the colophon is written: "Each man beneath his flag according to the house of their fathers... and he will merit to bestow a bountiful gift on anyone who grasps the Shield of David." In 1592, Mordechai Maizel was allowed to affix "a flag of King David, similar to that located on the Main Synagogue" to his synagogue in Prague. In 1648, the Jews of Prague were again allowed a flag, in acknowledgment of their part in defending the city against the Swedes. On a red background was a yellow Shield of David, in the centre of which was a Swedish star. [5]
A synagogue in Karlsruhe, Germany, with the outline of a Star of David
A synagogue in Karlsruhe, Germany, with the outline of a Star of David
A recruitment poster published in American Jewish magazines during WWI. Daughter of Zion (representing the Jewish people): I want your Old New Land! Join the Jewish regiment.
A recruitment poster published in American Jewish magazines during WWI. Daughter of Zion (representing the Jewish people): I want your Old New Land! Join the Jewish regiment.

The Star of David can be found on the tombstones of religious Jews going back hundreds of years in Europe, as it became accepted as the universal symbol of the Jewish people. Following Jewish emancipation after the French revolution, Jewish communities chose the Star of David to represent themselves, comparable to the cross used by most Christians.

Some Orthodox Jewish groups reject the use of the hexagram Star of David because of its association with magic and the occult. They do not recognize it as a Jewish symbol. Some Haredi groups, such as Neturei Karta and Satmar reject it because they associate it with Zionism.

Many Modern Orthodox synagogues, and many synagogues of other Jewish movements, however have the Israeli flag with the Star of David prominently displayed at the front of the synagogues near the Ark containing the Torah scrolls.

Use by the Nazis

See also: Yellow badge

The yellow badge
The yellow badge

A Star of David, often yellow-colored, was used by the Nazis during the Holocaust as a method of identifying Jews. After the German invasion of Poland in 1939 there were initially different local decrees forcing Jews to wear a distinct sign – in the General Government e.g. a white armband with a blue Star of David on it, in the Warthegau a yellow badge in the form of a Star of David on the right side of the breast and on the back.[6] The requirement to wear the Star of David with the word Jude (German for Jew) inscribed was then extended to all Jews over the age of 6 in the Reich and the Protectorate of Bohemia and Moravia (by a decree issued on September 1, 1941 signed by Reinhard Heydrich [7]) and was gradually introduced in other German-occupied areas, where local words were used (e.g. Juif in French, Jood in Dutch).

Jewish inmates in concentration camps were later forced to wear similar Nazi concentration camp badges.

Magen David Adom
The Magen David Adom emblem
The Magen David Adom emblem

Magen David Adom (MDA) (Red Star of David or, translated literally, Red Shield of David) is Israel's only official emergency medical, disaster, ambulance service. It is an official member of the International Committee of the Red Cross.

See also
The WikiProject Judaism Star of David
The WikiProject Judaism Star of David

* Chai symbol
* Flag of Israel
* Seal of Solomon
* Star of Bethlehem
* Merkaba

Notes

* In Unicode, the "Star of David" symbol is U+2721 (✡).

Footnotes

1. ^ Eshkol Ha-Kofer by Judah Hadassi, 12th century CE
2. ^ G.S. Oegema, Realms of Judaism. The history of the Shield of David, the birth of a symbol (Peter Lang, Germany, 1996) ISBN 3-631-30192-8
3. ^ Hatakh ha-Zahav, Hotam Shelomoh u-Magen-David (Poalim, 1990, Hebrew) p.156
4. ^ King Solomon-s Seal
5. ^ The National Flag at MFA
6. ^ Encyclopedia of the Holocaust (at Museum of Tolerance)
7. ^ Polizeiverordnung über die Kennzeichnung der Juden (came into force September 19, 1941)

Jewelry: Pewter

2005-03-09T09:29:00.000-08:00

Pewter is a metal alloy, traditionally between 85 and 96 percent tin, and the rest copper and/or lead. There were three grades of pewter: Fine, for eatingware, with 96 percent tin, and 4 percent copper; Trifle, also for eating and drinking utensils but duller in appearance, with essentially 92 percent tin, 4 percent copper, and up to 4 percent lead; and Lay or Ley metal, not for eating or drinking utensils, which could contain up to 15 percent lead. Modern pewter mixes the tin with copper, antimony and/or bismuth, as opposed to lead.

Physically, pewter is a bright, shiny metal that is very similar in appearance to silver. Like silver, pewter will also oxidize to a dull gray over time if left untreated. Pewter is a very malleable alloy, being soft enough to carve with hand tools, and it also takes good impressions from punches or presses. Some types of pewter pieces, such as candlesticks, would be turned on a metal lathe. Pewter has a low melting point, and duplication by casting will give excellent results.

Use of pewter was common from the Middle Ages up until the various developments in glass-making during the 18th and 19th centuries. Mass production of glass products has seen glass universally replace pewter in day-to-day life. Pewter artifacts continue to be produced, mainly as decorative or specialty items.

Unlidded mugs and lidded tankards are certainly the most commonly-known pewter artifacts from the 19th century, although the metal is also used for porringers, plates, cutlery and jewelry.

See: Pewter Menorahs

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Pewter.

Jewelry: Pearls

2005-03-07T09:25:00.000-08:00

Pearls are a hard, rounded object produced by certain mollusks, primarily oysters. Pearl is valued as a gemstone and is cultivated or harvested for Jewellery.

Pearls are formed inside the shell of certain bivalve mollusks. As a response to an irritating object inside its shell, the mollusk will deposit layers of calcium carbonate (CaCO3) in the form of the minerals aragonite or calcite (both crystalline forms of calcium carbonate) held together by an organic horn-like compound called conchiolin. This combination of calcium carbonate and conchiolin is called nacre, or as most know it, mother-of-pearl.

The unique luster of pearls depends upon the reflection and refraction of light from the translucent layers and is finer in proportion as the layers become thinner and more numerous. The iridescence that some pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. Pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green, blue, brown, or black. Black pearls were highly valued because of their rarity; however, this does not apply nowadays as black pearl production has significantly increased.

History

Before the beginning of the 20th Century, pearl hunting was the most common way of harvesting pearls. Divers manually pulled oysters from ocean floors and river bottoms and checked them individually for pearls. Not all natural oysters produce pearls, however. In fact, in a haul of three tones, only three or four oysters will produce perfect pearls.

Now, however, almost all pearls used for jewelry are cultured by planting a core or nucleus into pearl oysters. The pearls are usually harvested three years after the planting, but it can take up to as long as six years before a pearl is produced. This mariculture process was first developed by Kokichi Mikimoto in Japan, who was granted a patent for the process in 1896. The nucleus is generally a polished bead made from mussel shell. Along with a small scrap of mantle tissue from another oyster to serve as an irritant, it is surgically implanted near the oyster's genitals. Oysters which survive the subsequent surgery to remove the finished pearl are often implanted with a new, larger nucleus as part of the same procedure and then returned to the water for another three years of growth.

The original Japanese cultured pearls, known as Akoya pearls, are produced by a species of small oysters no bigger than 6 to 7 cm in size, hence Japanese pearls larger than 10 mm in diameter are extremely rare and highly priced. In the past couple of decades, cultured pearls have been produced with larger oysters in the south Pacific and Indian Ocean. One of the largest pearl-bearing oysters is the Pinctada maxima, which is roughly the size of a dinner plate. South Sea pearls are characterized by their large size and silvery color. Sizes up to 14 mm in diameter are not uncommon. Australia is one of the most important sources of South Sea pearls. Tahitian pearls (also referred to as Titian pearls) are also another South Sea pearl.

In the 1990s, Japanese pearl producers also invested in producing cultured pearls with freshwater mussels in the region of Shanghai, China, and in Fiji. Freshwater pearls are characterized by the reflection of rainbow colors in the luster. Cultured pearls are also produced using abalone.

Jewelry

The value of the pearls in jewelry is determined by a combination of the luster, color, size, lack of surface flaw and symmetry that are appropriate for the type of pearl under consideration. Among those attributes, luster is the most important differentiator of pearl quality according to jewelers. All factors being equal, however, the larger the pearl the more valuable it is. Large perfectly round pearls are rare and highly valued. Teardrop-shaped pearls are often used in pendants. Irregular shaped pearls are often used in necklaces.

Pearls come in eight basic shapes, round, semi-round, button, drop, pear, oval, baroque, and ringed. Perfectly round pearls are the rarest and most expensive, and are generally used in necklaces, or strings of pearls. Semi-rounds are also used in necklaces or in pieces where the shape of the pearl can be disguised to look like it is a perfectly round pearl. Button pearls are like a slightly flattened round pearl and can also make a necklace, but are more often used in single pendants or earrings where the back half of the pearl is covered, making it look like a larger, round pearl.

Drop and pear shaped pearls are sometimes referred to as teardrop pearls and are most often seen in earrings, pendants, or as a center pearl in a necklace. Baroque pearls have a different appeal to them than more standard shapes because they are often highly irregular and make unique and interesting shapes. They are also commonly seen in necklaces. Ringed pearls are characterized by concentric ridges, or rings, around the body of the pearl.

In general, cultivated pearls are less valuable than natural pearls, and imitation pearls are the least expensive. One way that jewellers can determine whether a pearl is cultivated or natural is by x-raying the pearl. If the grit in the centre of the pearl is a perfect sphere, then the jeweller knows it is cultivated. This is because when the cultivators insert the grit, (usually a polished piece of mussel shell), it is always perfectly round, so as to produce a more expensive, perfectly round pearl. If the centre is not perfectly round, the jeweller recognizes that it is genuine, and gives it a higher value. Imitation pearls are much easier to identify by jewellers. Some imitation pearls are simply made of mother-of-pearl, coral or conch, while others are made from glass and are coated with a solution containing fish scales called essence d'Orient. Although imitation pearls look the part, they do not have the same weight or smoothness as real pearls, and their luster will also dim greatly.

There is also a unique way of naming pearl necklaces. While most other necklaces are simply referred to by their physical measurement, strings of pearls have their own set of names that characterize the pearls based on where they hang when worn around the neck. A collar will sit directly against the throat and not hang down the neck at all, they are often made up of multiple strands of pearls. Pearl chokers nestle just at the base of the neck. The size called a princess comes down to or just below the collarbone. A matinee of pearls falls just above the breasts. An opera will be long enough to reach the breastbone or sternum of the wearer, and longer still, a pearl rope is any length that falls down further than an opera.

Necklaces can also be classified as uniform, where all the pearls are the same size, graduated, where the pearls are arranged in size from large in the centre to smaller at the ends, or tin cup, where pearls are generally the same size, but separated by lengths of chain.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Pearls.

Jewelry: Platinum

2005-03-06T09:33:00.000-08:00

Platinum

platinum, metallic chemical element; symbol Pt; at. no. 78; at. wt. 195.08; m.p. 1,772°C; b.p. 3,827±100°C; sp. gr. 21.45 at 20°C; valence +2 or +4. Pure platinum is a malleable, ductile, lustrous, silver-white metal with a face-centered cubic crystalline structure. Chemically inactive, it is unaffected by common acids but dissolves in aqua regia, forming chloroplatinic acid (H2PtCl6). It is attacked by the halogens, sulfur, or caustic alkalies. It does not combine with oxygen even at high temperatures. Like palladium, it absorbs large quantities of hydrogen, which it releases at red heat.

Platinum is found in nature alloyed with the other metals of the so-called platinum group, found in group VIII of the periodic table; the other five metals in this group are iridium, osmium, palladium, rhodium, and ruthenium. These metals are found in alluvial deposits in Russia, South Africa, Colombia, and Alaska. Platinum and the related metals are recovered commercially as a byproduct of the refining of nickel ores mined near Sudbury, Ont., Canada; from gold mines in South Africa; and from the alluvial deposits in Russia. There is no routine method for separating platinum from other metals; it is usually recovered by complex chemical methods.

Platinum has many uses. Its wear- and tarnish-resistance characteristics are well-suited for making fine jewelry. Platinum and its alloys are used in surgical tools, laboratory utensils, electrical resistance wires, and electrical contact points. The most important of the alloys are those with iridium. The International Prototype Kilogram, kept at Sèvres, France, is a cylinder of platinum-iridium alloy, and the standard definition of a meter for a long time was based on the distance between two marks on a bar of platinum-iridium. Platinum is also used in the definition of the Standard Hydrogen Electrode (a reference for determining cell voltages). Because its thermal coefficient of expansion is nearly equal to that of glass, platinum is used to make electrodes sealed in glass. It is used extensively in dentistry and a platinum-osmium alloy is used in implants such as pacemakers and replacement valves. A platinum-cobalt alloy is used to make very powerful magnets.

Platinum is specially prepared for use as a catalyst. Finely divided, the metal is platinum black, a powder. It also may be used as platinum sponge, formed when platinic ammonium chloride, (NH4)2PtCl6, is ignited, or as platinized asbestos, prepared by heating asbestos after dipping it in chloroplatinic acid. Platinum catalysts are used in the contact process for producing sulfuric acid, in the Ostwald process for the production of nitric acid, and in petroleum cracking, as well as in a variety of other reactions. Platinum is also used as a catalyst in fuel cells and in catalytic converters for automobiles.

Naturally-occurring platinum and platinum-rich alloys have been known since antiquity. Although there is evidence that the metal was used in the Americas in pre-Columbian times, the first European reference to platinum appears in 1557 as a description of a mysterious metal found in Central American mines. When the Spanish first encountered the metal, they regarded it as an undesirable impurity in the silver they were mining and often discarded it.

Modern knowledge of the metal dates from about 1736, when its existence in South America was reported by A. de Ulloa. Some of this platina [little silver], was taken to England, and soon thereafter many leading chemists published reports on it. A process discovered about 1803 by W. H. Wollaston for making the metal malleable made possible its commercial use for laboratory apparatus and other purposes. Although platinum was used as an adulterant for gold over a century ago, it is now considered the more valuable of the two.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Platinum.

Diamonds

2005-03-01T17:49:00.000-08:00

Diamond is the hardest known natural material (third-hardest known material after aggregated diamond nanorods and ultra hard fullerite), whose hardness and high dispersion of light make it useful for industrial applications and jewelry.

Diamonds are specifically renowned as a material with superlative physical qualities — they make excellent abrasives because they can be scratched only by other diamonds, Borazon, ultra hard fullerite, or aggregated diamond nanorods, which also means they hold a polish extremely well and retain their luster. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion. About 100,000 kg are synthesized annually.

The name “diamond” derives from the ancient Greek adamas (αδάμας; “invincible”). They have been treasured as gemstones since their use as religious icons in India at least 2,500 years ago— and usage in drill bits and engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. They are commonly judged by the “four Cs”: carat, clarity, color, and cut.

Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which brought to the surface the diamond crystals from deep in the Earth where the high pressure and temperature enables the formation of the crystals. The mining and distribution of natural diamonds are subjects of frequent controversy such as with concerns over the sale of conflict diamonds by African paramilitary groups. There are also allegations that the De Beers Group misuses its dominance in the industry to control supply and manipulate price via monopolistic practices, although in recent years the company's market share has dropped to below 50%.

Material properties

A diamond is a transparent crystal of tetrahedrally bonded carbon atoms. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness, its high dispersion index, and high thermal conductivity.

Hardness

Diamond is the hardest natural material known, its hardness set to 10, i.e. hardest, on Mohs scale of mineral hardness and having an absolute hardness value of between 90, 167, and 231 gigapascals in various tests. Diamond's hardness has been known since antiquity, and is the source of its name. However, aggregated diamond nanorods, an allotrope of carbon first synthesized in 2005, are now believed to be even harder than diamond.

The hardest diamonds in the world are from the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is considered to be a product of the crystal growth form, which is single stage growth crystal. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice all of which affect their hardness.

The hardness of diamonds contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well, keeping its luster over long periods of time. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in an engagement ring or wedding ring, which are often worn every day.

Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, or use of diamond powder as an abrasive. Industrial-grade diamonds are either unsuitable for use as gems or synthetically produced, which lowers their value and makes their use economically feasible. Industrial applications, especially as drill bits and engraving tools, also date to ancient times.

Electrical conductivity

Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most other diamonds, which are excellent electrical insulators.

Toughness

Toughness relates to a material's ability to resist breakage from forceful impact. The toughness of natural diamond has been measured as 3.4 MPa\sqrt{m} , which is good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond is therefore more fragile in some orientations than others.

Color

Diamonds can occur in nearly any color, though yellow and brown are by far the most common. "Black" diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. When the color is saturated enough in yellow or brown diamonds, a stone may be referred to as a fancy colored diamond by the gem trade, otherwise they are graded for color in the normal color range of white diamonds. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present. The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the normal color range, and applies a grading scale from 'D' (colorless) to 'Z' (light yellow). The GIA labels diamonds that have more color than a 'Z' diamond fancy, along with those that are any color other than yellow or brown.

Natural history

Formation

Diamonds are formed in numerous different ways. One way they are formed is by prolonged exposure of carbon-bearing materials to high pressure at comparatively low temperature. On Earth, the formation of diamonds is possible because there are regions deep within the Earth that are at a high enough pressure and low enough temperature that the formation of diamonds is thermodynamically favorable. Beneath thick continental crust ( in the lithospheric mantle of cratons), diamonds form starting at depths of about 150 kilometers (90 miles), where pressure is roughly 5 gigapascals and the temperature is around 1200 degrees Celsius (2200 degrees Fahrenheit). Diamonds rise to the Earth surfaces carried by the molten rock of kimberlite or lamproite diatremes. Diamonds cannot form beneath oceanic crust because the oceanic mantle is too hot at the appropriate depth. Thick continental lithosphere is cooler than asthenosphere at the same depth, reaching the required pressure at a low enough temperature for diamond stability. Long residence in the cratonic lithosphere allows diamond crystals to grow larger.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Diamonds.

Diamond -- History

2005-03-01T17:05:00.000-08:00

Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could then be found. The earliest written reference can be found in the Buddhist text, the Anguttara Nikaya another sanskrit text, the Arthashastra, which was completed around 296 BCE and describes diamond's hardness, luster, and dispersion. Diamonds quickly became associated with divinity, being used to decorate religious icons, and were believed to bring good fortune to those who carried them. Ownership was restricted among various castes by color, with only kings being allowed to own all colors of diamond.

In February 2005, a joint Chinese-U.S. team of archaeologists reported the discovery of four corundum-rich stone ceremonial burial axes originating from China's Liangzhu and Sanxingcun cultures (4000 BCE–2500 BCE) which, because of the axes' specular surfaces, the scientists believe were polished using diamond powder [2] [3]. Although there are diamond deposits now known to exist close to the burial sites, no direct evidence of coeval diamond mining has been found: the researchers came to this conclusion by polishing corundum using various lapidary abrasives and modern techniques then comparing the results using an atomic force microscope. At that scale, the surface of the modern diamond-polished corundum closely resembled that of the axes; however, the polishes of the latter were superior.

Diamonds were traded to both the east and west of India and were recognized by various cultures for their gemological or industrial uses. In his work Naturalis Historia, the Roman writer Pliny the Elder noted diamond's ornamental uses, as well as its usefulness to engravers because of its hardness. In China, diamonds seem to have been used primarily as diamond tools for engraving jade and drilling holes in beads. Archaeological evidence from Yemen suggests that diamonds were used as drill tips as early as the 4th century BCE. In Europe, however, diamonds disappeared for almost 1,000 years following the rise of Christianity because of two effects: early Christians rejected diamonds because of their earlier use in amulets, and Arabic traders restricted the flow of trade between Europe and India.

Until the late Middle Ages, diamonds were most prized in their natural octahedral state, perhaps with the crystal surfaces polished to increase luster and remove foreign material. Around 1300, the flow of diamonds into Europe increased via Venice's trade network, with most flowing through the low country ports of Bruges, Antwerp, and Amsterdam. During this time, the taboo against cutting diamonds into gem shapes, which was established over 1,000 years earlier in the traditions of India, ended allowing the development of diamond cutting technology to begin in earnest. By 1375, a guild of diamond polishers had been established at Nuremberg. Over the following centuries, various diamond cuts were introduced which increasingly demonstrated the fire and brilliance that makes diamonds treasured today: the table cut, the briolette (around 1476), the rose cut (mid-16th century), and by the mid-17th century, the Mazarin, the first brilliant cut diamond design. In 1919, Marcel Tolkowsky developed an ideal round brilliant cut design that has set the standard for comparison of modern gems; however, diamond cuts have continued to be refined.

The rise in popularity of diamonds as gems seems to have paralleled increasing availability through European history. In the 13th century, King Louis IX of France established a law that only the king could own diamonds. However, within a century diamonds were popular gems among the moneyed aristocratic and merchant classes, and by 1477 had begun to be used in wedding rings. Popularity continued to rise as new cuts were developed that enhanced the diamond's aesthetic appeal, and has largely continued unabated to this day; diamonds have proven popular with all classes in society as their cost has become within reach. A number of large diamonds have become historically significant objects, as their inclusion in various sets of crown jewels and the purchase, sale, and sometimes theft of notable diamonds, have sometimes become politicized.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Diamonds.

Jewelry: Karat - Carat

2005-03-01T09:20:00.000-08:00

Karat

A unit of measure for the fineness of gold, equal to 1/24 part. Pure gold is 24 karat; gold that is 50 percent pure is 12 karat.

Carat (mass)

A unit of weight for precious stones, equal to 200 milligrams.

Note: A carat can also be further divided into "points". There are 100 points to a carat.

The carat is a unit of mass used for gems, and equals 200 milligrams. The word derives from the Greek keration (fruit of the carob), via Arabic and Italian. Carob seeds were used as weights on precision scales because of their uniform size. In the past, different countries each had their own carat, roughly equivalent to a carob seed. However, in 1907 the metric carat of 200 milligrams was adopted, which is now universally used today.

Carat

The carat is a measure of the purity of precious metals and their alloys, such as gold. One carat in this sense is one twenty-fourth purity by weight. Therefore 24-carat gold is pure gold, 12-carat gold is 50% purity, etc. In the United States and Canada, the spelling karat is usually used for the measure of purity, while carat refers to the measure of mass.

The carat system is increasingly being complemented or superseded by the millesimal fineness system in which the purity is denoted by parts per thousand of pure metal in the alloy.

The most common carats used for gold in bullion, jewellry making and goldsmith are:

24 carat (millesimal fineness 999)
22 carat (millesimal fineness 916)
20 carat (millesimal fineness 833)
18 carat (millesimal fineness 750)
16 carat (millesimal fineness 625)
14 carat (millesimal fineness 585)
10 carat (millesimal fineness 417)
9 carat (millesimal fineness 375)

Agate

2005-02-01T07:19:00.000-08:00

Agate

Agate (ăg'ĭt) , translucent, cryptocrystalline variety of quartz and a subvariety of chalcedony. Agates are identical in chemical structure to jasper, flint, chert, petrified wood, and tiger's-eye, and are often found in association with opal. The colorful, banded rocks are used as a semiprecious gemstone and in the manufacture of grinding equipment. An agate's banding forms as silica from solution is slowly deposited into cavities and veins in older rock. The stones can be artificially stained to produce combinations of color more vivid than those found in the natural state. The cutting and staining of agates has long been centered at Idar-Oberstein, Germany. Important sources of agate are Brazil, Uruguay, and the United States (Oregon, Washington, and around Lake Superior). The moss agate or mocha stone contains visible impurities in the form of dendritic shapes that resemble moss. See onyx.

Types of agate

A Mexican agate, showing only a single eye, has received the name of "cyclops agate." Included matter of a green, golden, red, black or other colour or combinations embedded in the chalcedony and disposed in filaments and other forms suggestive of vegetable growth, gives rise to dendritic or moss agate (named varieties include Maury Mountain, Richardson Ranch, Sheep Creek and others). Dendritic agates have beautiful fern like patterns on them formed due to the presence of manganese and iron ions. Other types of included matter deposited during agate-building include sagenitic growths (radial mineral crystals) and chunks of entrapped detritus (such as sand, ash, or mud). Occasionally agate fills a void left by decomposed vegetative material such as a tree limb or root and is called limb cast agate due to its appearance.

Turritella agate is formed from fossil Turritella shells silicified in a chalcedony base. Turritella are spiral marine gastropods having elongated, spiral shells composed of many whorls. Similarly, coral, petrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey agate or stone.

Certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due to the extreme delicacy of the successive bands, whence they are termed rainbow agates. Often agate coexists with layers or masses of opal, jasper or crystalline quartz due to ambient variations during the formation process.

Other forms of agate include carnelian agate (usually exhibiting reddish hues), Botswana agate, Ellensburg blue agate, blue lace agate, plume agate (such as Carey, Graveyard Point, Sage, St. Johns, Teeter Ranch and others), tube agate (with visible flow channels), fortification agate (which exhibit little or no layered structure), fire agate (which seems to glow internally like an opal) and Mexican crazy-lace agate (which exhibits an often brightly colored, complex banded pattern).

Agate beliefs

In many traditions agate is believed to cure the stings of scorpions and the bites of snakes, soothe the mind, prevent contagion, still thunder and lightning, promote eloquence, secure the favour of the powerful, and bring victory over enemies. Persian magi are also known to have prized agate rings in their work and beliefs.

Industry uses agates chiefly to make ornaments such as pins, brooches, paper knives, inkstands, and seals. Because of its hardness and ability to resist acids, agate is used to make mortars and pestles to crush and mix chemicals.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Agate.

Gold

2005-01-01T07:11:00.000-08:00

Gold

Gold, metallic chemical element; symbol Au [Lat. aurum=shining dawn]; at. no. 79; at. wt. 196.9665; m.p. 1,064.43°C; b.p. 2,808°C; sp. gr. 19.32 at 20°C; valence +1 or +3.

Gold is very ductile and is the most malleable metal; it can be beaten into extremely thin sheets of gold leaf. Only silver and copper, which are above it in group Ib of the periodic table, are better electrical conductors. Gold is chemically inactive. It is unaffected by moisture, oxygen, or ordinary acids but is attacked by the halogens. Aqua regia (a mixture of nitric and hydrochloric acids that liberates chlorine) is so named for its ability to dissolve gold, the “king” of the metals. Gold forms both aurous (univalent) and auric (trivalent) compounds; auric chloride and chloroauric acid are its most common compounds.

A relatively soft metal, gold is usually hardened by alloying with copper, silver, or other metals. White gold, a substitute for platinum, is an alloy of gold with platinum, palladium, nickel, or nickel and zinc. Green gold, also used by jewelers, is usually an alloy of gold with silver. Alloys of gold with copper are a reddish yellow and are used for coinage and jewelry. Gold is often found in nature alloyed with other metals; when more than 20% of silver is present the alloy is called electrum. The gold content of an alloy is commonly stated in carats, a carat being 1/24 part by weight of the total mass. Pure gold is therefore 24 carats fine; an alloy that is 75% gold is 18 carats fine. Fineness is sometimes expressed in terms of parts per thousand; thus gold containing 10% of other metals is said to have a fineness of 900.

Gold is widely distributed on the earth; although large amounts are present also in seawater, the cost of current methods for recovering it exceeds its value. Most gold is found in the metallic state in the form of dust, grains, flakes, or nuggets. It occurs, usually in association with silver or other metals, in quartz veins or lodes so finely disseminated that it is not visible. It is found also in alluvial placer deposits, which are worked by panning, dredging, and hydraulic mining. Gold is extracted from its ores by mechanical means and separated from other metals by chemical processes, notably the cyanide process, the amalgamation process, and the chlorination process (in this the ore is oxidized and chlorinated and the gold precipitated with hydrogen sulfide). It also occurs in compounds, notably telluride minerals.

Gold has been known from prehistoric times and was possibly the first metal used by humans. It was valued for ornaments, and magical efficacy was attributed to it. In the Middle Ages alchemists sought to transmute baser metals into gold. The quest for gold stimulated European explorations and conquests in the Western Hemisphere, and its discovery has led to many a gold rush. The chief producers are South Africa, the United States (especially in South Dakota and Nevada), Australia, China, Canada, and Russia. For a discussion of the monetary function of gold, see bimetallism; coin; international monetary system; money.

Also see	Gold History	What is a Troy Ounce?
	Jewelry History
	Gems Index

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Gold.

Hallmarks

2003-03-01T06:31:00.000-08:00

A hallmark is an official marking made by a trusted party, usually an assay office, on items made of precious metals (Platinum, Gold and Silver) that guarantees a certain purity of the metal. This should not be confused with a marking, often just a number such as 925, which is done voluntarily by the manufacturer, and unfortunately does not always reflect the true purity of the metal. A hallmark is only applied after the item has been assayed to determine its purity. Often the hallmark is made up of several elements including: the type of metal, the maker and the year of the marking.

History of hallmarking

Hallmarking may have begun as long ago as the sixth century AD. Byzantine silver from this time has a system of five marks which have not been completely deciphered.

Hallmarking is Europe's earliest form of consumer protection. Hallmarking probably started in France, the standard for silver being established in 1260, but the first town mark was established in 1275.

In 1300, King Edward I of England enacted a statute ordering that all silver articles must meet the Sterling silver standard (92.5% pure silver), and should be assayed by 'guardians of the craft', who would then mark the item with a leopard's head.

In 1327, King Edward III of England granted a charter to the Worshipful Company of Goldsmiths (more commonly known as the Goldsmiths' Company), marking the beginning of the Company's formal existence.

In 1355, individual maker marks were introduced in France, which was mirrored in England in 1363, adding accountability to the two systems.

In 1427, the date letter system was established in France, allowing the accurate dating of any hallmarked piece.

In 1478, the Assay Office was established in Goldsmiths' Hall. At this time, the date letter system was introduced in England.

In 1697, a higher standard of silver, known as the Britannia standard (95.8% silver) was made compulsory in England to protect the new coinage which was being melted down by silversmiths for the silver. The Sterling standard was restored in 1720.

In 1975, the 1973 Hallmarking Act was enacted, introducing Platinum marking. All four remaining assay offices finally adopted the same date letter sequences.

The latest changes in 1999 were made to the UK hallmarking system to bring the system closer into line with the European Union (EU).

International hallmarking has been plagued by difficulties, because even amongst countries which implement hallmarking, standards and enforcement varies considerably, making it difficult for one country to accept another's hallmarking as equivalent to its own.

Modern hallmarks

United Kingdom hallmarks

Pictured here are the assay office marks - from left to right, the leopard's head of London, the anchor of Birmingham, the Yorkshire rose of Sheffield, and the castle of Edinburgh.

As it now stands, the compulsory part of the UK hallmark consists of the sponsor or maker's mark, the assay office mark, and the standard of fineness (in this case silver, 925 parts in 1000). These are shown in the top of the two example hallmarks. The bottom example shows the extra marks that can also be struck, the lion passant, indicating Sterling silver, the date mark (lowercase a for '2000'), and in this example, the 'Millennium mark', which was only available for the years 1999 and 2000. The bottom example bears the Yorkshire rose mark for the Sheffield Assay Office.

Vienna Convention hallmarks

Marking techniques

Punching

Traditionally, the hallmarks are 'struck' using steel punches. Punches are made in different sizes, suitable for tiny pieces of jewellery to large silver platters. Punches are made in straight shank or ring shank, the former for normal punching with a hammer, and the later used with a press to mark rings. The problem with traditional punching is that the process of punching displaces metal, causing some distortion of the article being marked. This means that re-finishing of the article is required after hallmarking. For this reason, and that off-cuts from sprues are often used for assay, many articles are sent unfinished to the assay office for assay and hallmarking.

Laser marking

A new method of marking using lasers is now available, which is especially valuable for delicate items and hollowware, which would be damaged or distorted by the punching process. Laser marking also means that finished articles do not need to be re-finished. Laser marking works by using high power lasers to evaporate material from the metal surface. Two methods exist, 2D and 3D laser marking. 2D laser marking burns the outline of the hallmarks into the object, while 3D laser marking better simulates the marks made by punching.

Also see	Silver
	Sterling Silver
	Gems Index

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Hallmark

Jewish Jewelry - Sapphires

2003-03-01T06:13:00.000-08:00

Sapphire

Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminum oxide (Al2O3), a mineral known as corundum. It can be found naturally as gemstones or manufactured in large crystal boules for varied applications, including infrared optical components, watch faces, high-durability windows, and wafers for the deposition of semiconductors such as GaN nanorods.

The corundum group consists of pure aluminum oxide. Trace amounts of other elements such as iron, titanium and chromium give sapphires their blue, yellow, pink, purple, orange or greenish color. Sapphire includes any gemstone quality varieties of the mineral corundum except the fully saturated red variety, which is instead known as ruby.

Historical and cultural references

Also see Jewish Jewelry

Sapphires have an esteemed history. Tradition holds that the tablets containing the Ten Commandments were composed of sapphire, so strong that a hammer swung against them would be smashed to pieces.

Supernatural powers were attributed to gems in India. One way this was manifested was the interdependence between gems and planets. Ruby, associated with the Sun, was the Lord of Gems, for the Sun lorded over all the planets. Blue sapphire is associated with Saturn (Wojtilla, 1973), yellow sapphire with Jupiter.

Natural Sapphire

Blue Sapphire

Various shades of blue result from titanium and iron inclusions within the aluminum oxide crystal lattice. Some stones are not well saturated and show tones of gray. It is common to bake natural sapphires to improve color. This is usually done by heating the sapphires to temperatures of up to 1800°C for several hours, or by heating in a nitrogen deficient atmosphere oven for 7 days or more. On magnification the silk due to included rutile needles are visible. If the needles are unbroken, then the stone was not heated. If the silk is not visible then the stone was heated adequately. If the silk is partially broken then a process known as low tube heat was used. Low tube heat is the process where the rough stone is heated to 1300 °C for 20 to 30 minutes over charcoal. This takes out any gray or brown in the stone and improves color saturation.

Fancy color sapphire

Sapphire is the birthstone associated with September.
The 45th wedding anniversary is known as the sapphire anniversary.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Sapphire.

The History of Jewelry: Sapphires

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