Diamond Fats

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

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

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

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

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

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

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

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)