Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925. Fine silver is 99.9% pure and is generally too soft for producing jewellery supplies; therefore, the silver is usually alloyed with copper to give it strength while preserving the ductility and beauty of the precious metal.