Alloy

A mixture of two or more pure metals. In the case of gold, a mixture with one or more metals, often base metals such as copper, zinc and silver, to lower the purity, influence the colour or add hardness and strength. Originally from the Latin alligare, to bind up.

Alloys of gold are used both for coins and jewellery and are usually made by semi-fabricators for the jewellery trade, although some jewellery manufacturers make their own alloys.

The most common alloys are 22, 21, 18, 14, 9 and 8 carat, but may be made to other standards in some countries, such as 19.2 carat in Portugal.

The colour of the alloy depends on the balance of other metals with which gold is mixed. In coloured golds, red shades are achieved by increasing the copper content at the expense of silver and zinc; pale yellow and green shades are achieved by increasing the silver and/or zinc content at the expense of the copper.

At a given gold level, copper-rich golds tend to be harder than silver-rich golds. White golds are achieved by alloying with nickel or palladium, often with some zinc and copper to improve malleability. Nickel has a better hardening effect than palladium.

A hard gold is made by alloying with one per cent titanium (‘990 gold’) which may be defined as 24 carat in some markets such as chuk kam jewellery. The alloying additions to gold may be added as a pre-alloy or ‘master alloy'.