Fourrée

A fourrée is a coin, most often a counterfeit, that is made from a base metal core that has been plated with a precious metal to look like its solid metal counterpart. The term is normally applied to ancient silver-plated coins such as the Roman denarius and Greek drachma, but the term is also applied to other plated coins.

Cicero mentions that M. Marius Gratidianus, a praetor during the 80s BC, was widely praised for developing tests to detect false coins, and removing them from circulation. Gratidianus was killed under Sulla, who introduced his own anti-forgery law (lex Cornelia de falsis), that reintroduced serrated edges on precious metal coins, an anticounterfeiting measure that had been tried earlier.

Serrated denarii, or serrati, which featured about 20 notched chisel marks on the edge of the coin, were produced to demonstrate the integrity of the coin. This effort was in vain, as examples of fourrée serrati attest.

Production of fourrées began almost as early as the production of the first coins in Asia Minor in the 7th century BC. These coins were produced by people wishing to profit by producing a counterfeit containing less precious metal content than its purported face value. The most common method for producing a fourrée was to take a flan of copper, wrap it with silver foil, heat it, and strike it with the dies. If the coin was sufficiently heated and struck hard enough, a layer of eutectic alloy (a mixture of 72% silver and 28% copper that has the lowest melting point of any mixture of these two metals) would be produced, fusing the layers together. Sometimes eutectic was sprinkled between the layers to increase the bond. Exposure of the deception was often due to wear at the high points of the coin, or moisture trapped between the layers that caused the foil to bubble and then break as the core corroded.

A later method for making fourrées involved adding silver to the base metal coin after it had been struck. This method allowed even less silver to be used, which became more important in order to make counterfeiting profitable as the official coinage was debased. The exact method by which these coins were silvered is unclear, although possible methods include dipping the coin in molten silver, brushing the coins with molten silver, or dusting the coin with powdered silver and heating it until the silver melted.

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Wikipedia