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The carat system is increasingly being complemented or superseded by the millesimal fineness system in which the purity is denoted by parts per thousand of pure metal in the alloy.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