Gold is a highly sought-after precious metal in the world. One of the oldest precious metal in the history of mankind, it had been used as money, as a store of value, in jewellery, in sculpture, in medicine, in electronics and for ornamentation. Gold does not tarnish, rust or corrode. Due to its wonderful qualities and its magnificent luster, gold is considered the most important metal in jewellery making.
The purity of gold is measured in terms of karats. Pure gold is designated as 24 karat. A karat is the percent of pure gold in the alloy. One can determine the percentage of pure gold in any gold piece by dividing the karat by 24 (e.g., 18 karat gold: 18/24 = 0.750 = 75% pure gold).
As pure gold is soft, it is frequently mixed or alloyed with other metals in order to make the gold harder to be used for jewellery. Also mixing of gold with other metals affects the colour. For example, gold must be alloyed with different metals such as silver, nickel, palladium, copper, bronze, aluminium in order to get different shades of gold i.e. yellow gold, white gold, green gold.
The karat scale is used for measuring the proportion of gold in jewellery. Accordingly, 24 karat denotes pure gold. 18 karat gold is 75 % gold and 25 % alloy, and so forth.

In India, 18 karat and 22 karat are the most popular forms of gold jewellery. The 18 karat is popular because of its rich colour and durability.

Gold alloys can also affect the colour of gold. The following list includes the most common colours of gold alloys and the metals used for producing them: