The oldest gold objects excavated date to around 4400 BC; the oldest evidence of the use of gold in jewellery making comes from Egypt around 4000 BC. The malleability, lustre and beautiful rich colour or natural gold has always been its appeal. Compared with other precious metals, gold is also relatively easy to extract from the earth and process. Our present day purity system comes from a Byzantine coin called the Solidus which could be split into 24 'Keratia'. We express the amount of gold in an alloy in parts of 24. Therefore, 18ct gold is 18/24 parts gold or 75% pure. Some jewellery is marked 750 as opposed to 18ct. Different alloys lend different colours to the gold. Adding copper results in a nice warm rose gold; adding lots of copper gives a red gold. White gold is a little different.
Traditionally, zinc and nickel were blended with the gold to give the white colour. Today, nickel is rarely used because of the amount of people who suffer an allergic reaction to it. White gold is nearly always plated with rhodium, a member of the platinum family. Rhodium gives a mirror-like finish but will need replating from time to time.