Bi-metallic coins

Bi-metallic coins are coins consisting of two (bi-) metals or alloys, generally arranged with an outer ring around a contrasting center. Common circulating examples include the €1, €2, 2 and 5 PLN, 50 CZK, 100 and 200 HUF, 1 BGN, British £2, Canadian $2, South African R5, Turkish 1 lira, IDR 1K, Hong Kong $10, Argentine $1, Philippine P10.00 coin and all Mexican coins of $1 or higher denomination.

Bi-metallic coins have been issued for a long time, with examples known dating from the 17th century, while the Roman Empire issued special occasion, large medallions with a center of bronze or copper and an outer ring of orichalcum, starting with the reign of Hadrian. The silver-center cent pattern produced by the United States in 1792 is another example. In the 1830s and 1840s, British medalist Joseph Moore produced large numbers of bi-metallic "penny model" and less common "halfpenny model" tokens, as a proposal to replace the relatively large penny and halfpenny coins. Though not legal tender, Moore's tokens were circulated widely and accepted at face value by many merchants. Despite their popularity, the Royal Mint rejected the proposal, and did not reduce the size of the penny and halfpenny until decimalization.

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