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, for example 99.9% pure silver, is generally too soft for producing functional objects; therefore, the silver is usually alloyed with copper to give it strength while preserving the ductility and appearance of the precious metal. Other metals can replace the copper, usually with the intention of improving various properties of the basic sterling alloy such as reducing casting porosity, eliminating firescale, and increasing resistance to tarnish. See "Sterling silver". Wikipedia. Retrieved 2015-06-03.