The
fineness of a
precious metal refers to the
ratio by weight of the primary
metal to any added
base metals or
impurities. Many precious metals are used in the form of alloys. Other metals are added to increase
hardness, to make the metal more practical for use in such items as
coins and
jewelry, or to decrease the cost of the
alloy. For example,
copper is added to the precious metal
silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making
silver coins in the past, contains 90% silver and 10 opper, by
mass.
Sterling silver contains 92.5% silver and 7.5%, by mass, of other metals, usually copper.