A base metal is a common, cheap metal. Typical examples are lead and iron which, like other base metals, tarnish or oxidize on exposure to air or moisture. Such properties distinguish base metals from gold, platinum, and silver and other so-called precious or noble metals. In chemical terms, base metals are those at the negative end of the electrochemical series. In ancient times, it was an unfulfilled ambition of alchemists (see alchemy) to convert base metals into gold.