Carat (purity)

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For other uses of the word "carat," see Carat.

Carat or karat is a measure of the purity of gold and platinum alloys. 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 (see Carat). As a measure of purity, one carat is one twenty-fourth purity by weight:

[ X \mathbf = 24 \frac ]

where

X is the karat rating of the material,

[ M_g ] is the mass of pure gold or platinum in the material, and

[ M_m ] is the total mass of the material.

Therefore 24-carat gold is pure gold (99.99%), 12-carat gold is 50% purity, etc.

The carat system is increasingly being complemented or superseded by the millesimal fineness system in which the purity of precious metals is denoted by parts per thousand of pure metal in the alloy.

The most common carats used for gold in bullion, jewellery making and goldsmithing 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)

External link

[22 versus 24 carat gold coins]

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Carat (purity)

See also

External link