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.
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 elements other than copper can be used in alloys to reduce tarnishing, as well as casting porosity and fire scale.
Oxidized silver (black coloring in the silver) is a process that many jewelers use to give sterling silver a black patina. It gives the jewelry an antique or tarnished look. The process consists of taking clean sterling silver and using a chemical (liver of sulfur) to treat it to speed up the tarnishing effect.