Gold carat is used to mark the purity or gold content in an alloyed metal. Purity levels are measured in units of fineness per 1000 parts from highest concentration to lowest. For example, 9ct gold with 375 per 1000 parts is equivalent to 37.5% and for 18ct gold, 750 or 75% of the alloy being gold content. The Diamond Setter's yellow gold is alloyed with silver, zinc and a touch of copper with the amounts of each varying in 9ct, 14ct and 18ct. All our metal composition complies with UK and EU laws. The Diamond Setter uses 925 sterling silver as standard.