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Gold A relatively soft
metal, gold is usually hardened by alloying with
copper, silver, or other metals. White gold, a
substitute for platinum, is an alloy of gold with
platinum, palladium, nickel, or nickel and zinc. Green
gold, also used by jewelers, is usually an alloy of
gold with silver. Alloys of gold with copper are a
reddish yellow and are used for coinage and jewelry.
Gold is often found in nature alloyed with other
metals; when more than 20% of silver is present the
alloy is called electrum. The gold content of an alloy
is commonly stated in carats, a carat being 1/24 part
by weight of the total mass. Pure gold is therefore 24
carats fine; an alloy that is 75% gold is 18 carats
fine. Fineness is sometimes expressed in terms of
parts per thousand; thus gold containing 10% of other
metals is said to have a fineness of 900. |
