karat

Measure of the purity (fineness) of gold, or its proportion in an alloy. Pure gold is defined as 24 karats or having a fineness of 1000: one karat equal to 41.66 fineness. A 22 karat gold-alloy, for example, has 22 parts gold and 2 parts other metal (usually copper), and has fineness of 916.66 (is 91.666 percent pure gold). Similarly, an 18 karat gold-alloy is 75 percent pure gold. In the UK both carat and karat are spelled as carat, while in Germany both are spelled as karat.