A measure of gold purity in 24ths by weight, so that 18 parts gold in 24 makes an alloy 75% gold.
A karat is one part in 24 of an alloy’s weight in gold. Fine gold is 24 karat; 18 karat gold is 18 parts gold in 24, or 75%. British hallmarks show the standards as fineness in parts per thousand: 375, 585, 750 and 916 for 9, 14, 18 and 22 karat. The rest is other metals, added for strength and color (see precious metals); GIA finds 14 and 18 karat better suited than the softer 24 karat to rings worn every day.
Under the US FTC jewelry guides, gold without qualification should mean fine, 24 karat gold. An alloy should carry its karat immediately before the word, as in “14 Karat Gold” or “14 Kt. Gold”.
A karat is not a carat, the unit of mass for gemstones: 200 milligrams. British English prefers carat for gold as well, so 18 carat gold in Britain states a purity, not a weight; almost everyone abbreviates the gold measure as K, as in 18K.
In job listings
Karat appears in workshop and development roles, usually as a figure: polishers and repair artisans finish and restore pieces in 18 karat gold and platinum, casting coordinators prepare precious metal alloys, and research interns develop precious alloys for watchmaking. See current precious alloy roles.
