Gold, one of the most precious metals in the world, has been used in making jewelry and decorative artifacts for thousands of years. Most gold jewelry today is inscribed with a hallmark or karat measurement to indicate gold purity.
Also known by the chemical abbreviation Au, gold is one of the softest pure metals. This makes it highly malleable, meaning it is able to be hammered or pressed out of shape without cracking. It is also the most ductile of all metals, easily molded into wire.
When used for jewelry, gold is usually in alloy form. This means the gold is first mixed with other metals, such as silver. Alloying provides a harder solid to work with that is less likely to become deformed, and also confers color variation between blends.
Gold purity is measured in karats (k), with 100 percent gold designated as 24k. Many jewelers will imprint a three-digit hallmark into gold jewelry that indicates gold content in parts per thousand. For example, a bracelet that has "925" inscribed on it is 925/1,000 parts gold, or 92.5 percent gold (22.2k).