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 22 karat gold: 22/24 = 0.916 = 91.6% 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.

The karat scale is used for measuring the proportion of gold in jewellery. Accordingly, 24 karat denotes pure gold. 22 karat gold is 91.6% gold, 18 karat gold is 75 % gold and 25 % alloy, and so forth.

Our east Indian jewellery is made of 22 karat.  Jewllery from middle east are generally 21 kt.    Diamonds are set in 10, 14, 18 kt  gold  or Platinum. The 22 karat gold is popular because of its rich colour and design.

Gold alloys can also affect the colour of gold. 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, rose gold.