Units of purity

Carat is a measure of the purity of gold and platinum alloys. 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 The carat system is increasingly being complemented or superseded by the millesimal fine ...

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