In chemistry, the term base metal is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with diluted hydrochloric acid (HCl) to form hydrogen. Examples include iron, nickel, lead and zinc. Copper is considered a base metal as it oxidizes relatively easily, although it does not react with HCl.
Base is used in the sense of low-born, in opposition to noble or precious metal. In alchemy, a base metal was a common and inexpensive metal, as opposed to precious metals, mainly gold and silver. A long-time goal of the alchemists was the transmutation of base metal into precious metal.
In mining and economics, base metals refers to industrial non-ferrous metals excluding precious metals. These include copper, lead, nickel and zinc. The U.S. Customs and Border Protection is more inclusive in its definition. It includes, in addition to the four above, iron and steel, aluminium, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium.
In the context of plated metal products, the base metal underlies the plating metal, as copper underlies silver in Sheffield plate.
See also 
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