Gold

Gold is not used in its pure form as it is too soft to be used for jewellery manufacture. It should be noted that the tarnish and corrosion resistance of gold decreases with decreasing gold content.

Alloys of Gold

Gold is usually alloyed not only to improve its hardness and strength, but also to change its colours and make it more attractive. Most jewellery is normally made using an alloy of 75% gold as it has excellent tarnish and corrosion resistance, and also has good strength and ductility. A wide range of colour can be obtained using this proportion of gold. By adding mostly copper in the alloying process, red golds can be produced. Green golds are obtained by increasing the silver content while yellowish gold is manufactured by using equal amounts of silver and copper. Zinc is added occasionally to offset the reddish hue imparted by the copper. The proportions of the alloying additions directly affect the mechanical properties of the coloured carat golds. Copper considerably increases the strength of the gold. However, silver and gold atoms are almost similar in size. As a result, lattice distortion is small and the strengthening effect goes down accordingly.

White gold is widely used in jewellery manufacture. It is made by alloying gold with nickel or palladium, or both. In general, the more nickel is added, the harder the alloy becomes. Palladium golds, on the other hand, are generally very soft.