Sterling silver is an alloy of silver containing 92.5% by weight of silver and 7.5% by weight of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925.
Fine silver, for example 99.9% pure silver, is relatively soft, so silver is usually alloyed with copper to increase its hardness and strength. Sterling silver is prone to tarnishing, and metals other than copper can be used in alloys to reduce tarnishing, as well as casting porosity and firescale. Such metals include germanium, zinc, platinum, silicon, and boron. Recent examples of alloys using these metals include Argentium, Sterlium, Sterilite, and Silvadium.https://en.wikipedia.org/wiki/Sterling_silver