Crown gold

Crown gold is a 22 kt (carat) gold alloy, introduced in England for gold coin manufacture in 1526 (by Henry VIII) on the basis of superior wear properties, and perhaps to save the state mint costs. It is 22/24 = .91667 fine or 91.667% gold. Previously, gold sovereign coins were made from 23 kt gold, but this was soft and invited deliberate filing, and also non-intentional wear.

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The alloying metal is usually copper, although silver has been used. Crown gold remains the standard used in the British gold sovereign, which is still minted, and also in all U.S. circulation gold coins, including one of the two modern U.S. bullion coins, the American Gold Eagle.

Other than historical bullion coins in the U.S. and U.K., gold bullion coins are usually 24 kt (.999 fine or .9999 fine). In 2006, the United States introduced a new bullion coin - the American Buffalo - that used "pure" gold instead of crown gold due to the coin's not being intended for general circulation (meaning that durability isn't as big an issue).

References

• Metal Used in Coins and Metals by Tony Clayton