Gold, one of the most precious metals in the world, has been used in making jewellery and decorative artefacts for thousands of years. Most gold jewellery today is inscribed with a hallmark or carat 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 moulded into wire.
When used for jewellery, 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 colour variation between blends.
Gold purity is measured in carats (k), with 100 per cent gold designated as 24k. Many jewellers will imprint a three-digit hallmark into gold jewellery 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 per cent gold (22.2k).
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