A friend shows you a beautiful ring that she says is made from pure gold. Your friend is lucky to have such a valuable object. The purity of gold is expressed in units called karats. Gold that is 100 percent pure is labeled 24-karat gold. Gold jewelry that has a 12-karat label is only 50 percent gold. Jewelry that has an 18-karat label is 75 percent gold.
The surface of an object made from pure gold can easily be worn away by contact with other objects or dented because gold is a soft metal. When silver, copper, nickel, or zinc is mixed with gold, the gold is harder and more resistant to wear. These gold mixtures are alloys. An alloy is a mixture of two or more elements, at least one of which is a metal. Alloys have the characteristic properties of metals.
Milestones in Metallurgy
The science of metallurgy includes ways to extract metals from ores, refine metals, and use metals. Described here are some advances in metallurgy since 1850.