A base metal is a common and inexpensive metal, as opposed to a precious metal such as gold or silver. A long-time goal of alchemists was the transmutation of a base (low grade) metal into a precious metal. In numismatics, coins often derived their value from the precious metal content; however, base metals have been also used in coins in the past and today.
A base metal may be distinguished by oxidizing or corroding relatively easily and reacting variably with diluted hydrochloric acid (HCl) to form hydrogen. Examples include iron, nickel, lead and zinc. Copper is also considered a base metal because it oxidizes relatively easily, although it does not react with HCl.
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.