The coinage metals comprise those metallic chemical elements and alloys which have been used to mint coins. Historically, most coinage metals are from the three nonradioactive members of group 11 of the periodic table: copper, silver and gold. Copper is usually augmented with tin or other metals to form bronze. Gold, silver and bronze or copper were the principal coinage metals of the ancient world, the medieval period and into the late modern period when the diversity of coinage metals increased. While coins are primarily made from metal, some non-metallic materials have also been used.
History
Early coinage made from metal came into use during the Axial Age in the Greek world, in northern India, and in China, as coins became a widespread embodiment of money. Bronze, gold, silver and electrum (a naturally occurring pale yellow mixture of gold and silver that was further alloyed with silver and copper) were used. Silver coins from about 700 BC, are known from Aegina Island. Early electrum coins from Ephesus, Lydia date from about 650 BC. Ancient India in 6th century BC, was also one of the earliest issuers of coins in the world.
The gold Croeseids, issued in Lydia, were the first true gold coins with a standardized purity for general circulation. The gold and silver Croeseids formed the world's first bimetallic monetary system, c. 550 BC. The Persian daric was also an early gold coin which, along with a similar silver coin, the siglos, (from Ancient Greek σίγλος, Hebrew שֶׁקֶל (shékel)) represented the bimetallic monetary standard of the Achaemenid Persian Empire. These coins were also very well known in the Persian and Sassanids era, most notably, in Susa and in Ctesiphon.
Precious metals were used historically in commodity money and are found in bullion coins and some collectable coins. Coins functioning as fiat money are now made from a larger variety of base metals.
Requirements for a coinage metal
Coins that are intended for circulation may circulate for decades and thus must have excellent resistance to wear and corrosion. Achieving this goal typically necessitates the use of base metal alloys. In addition, some metals, such as manganese, are unsuitable as they are too hard to take an impression well or are apt to wear out stamping machines at the mint.
When minting coins, especially low denomination coins, there is a risk that the value of metal within a coin is greater than the face value, leading to negative seigniorage. This leads to the possibility of smelters taking coins and melting them down for the scrap value of the metal. Pre-1992 British pennies were made of 97% copper; but as of 2008, based on the price of copper, the value of a penny from this period is 1.5 new-pence. Modern British pennies are now made of copper-plated steel. For similar reasons, American cents were once made of copper alloys, but since 1982 have been made of copper-plated zinc.
Cupronickel, a common base metal alloy with varying proportions of copper and nickel, was introduced as a cheaper alternative for silver in coinage. Cupronickel, most commonly 75% copper, 25% nickel, has a silver color, is hard wearing and has excellent striking properties, essential for the design of the coin to be pressed accurately and quickly during manufacture. However, in the 21st century with the prices of both copper and nickel rising, it has become common to experiment with various alloys of steel, often stainless steel as an even cheaper alternative. For example, in India some coins have been made from a stainless steel that contains 82% iron, 18% chromium, and many other countries that have minted coins that contain metals now worth nearly the coin face-value, are experimenting with various steel alloys. Italy had earlier experimented with acmonital, a stainless steel alloy, for its coins
A number of more exotic metals have been used to make demonstration or fantasy coins which have never been used to make monetized coins for any nation-state, but could be. Some of these elements would make excellent coins in theory (e.g. zirconium). More expensive metals that are intrinsically valuable as commodities are less practical as coinage due to their cost, but could be used for bullion.