Recoinage. Melting one class of coins and using the metal to fabricate a new class of coins, or to retire the metal from the old class and issue new coins in a different composition. In a way, recoinage goes on constantly as old, worn coins are withdrawn from circulation, and melted for the metal these contain. However some notable recoinages have taken place in history. In 1696 the Tower Mint in London could not produce a new silvercoinage fast enough to replace existing coins, so country mints (Bristol, Chester, Exeter, Norwich and York) – under control of Sir Issac Newton – were called upon to aid in striking the new coins. As it was, it required two years to complete the recoinage.

During the silver shortage in England from 1790-1815 the Bank of England accumulated a supply of Spanish silver eight reales coins for emergency use. To make them acceptable in circulation they were sent to Matthew Boulton to be overstruck at his foundry in Soho where dies were made with an appropriate design and the inscription BANK OF ENGLAND 1804. In many cases these five-shilling pieces show traces of the old Spanish coins as the UNDERTYPE.

In more modern times extensive recoinage has occurred twice in the 20th century. In 1920 Great Britain effectively went off the sterlingstandard, cutting the silver content of their coins in half, replacing silver coins with a quaternary coinage (of silver, copper, nickel, zinc). In 1947 Great Britain replaced even that coinage with an all cupro-nickelcoinage. Major economic factors, as the rising price of coin alloys, cause drastic changes in coin compositions (necessitating recoinages). Smaller countries usually follow the actions of major countries.

For a brief time during recoinage, both coins circulate simultaneously. In the 20th century, machines were developed to separate out the old coins until only the new coins remain in circulation. The separation can be done by several ways; often, however, mechanical or magnetic separation cannot be used, so is used to distinguish between the two compositions. These separating machines are usually developed by the vending machine industry because of their experience with detecting good coins from bad in their machines.

Reference:

CH23 {1954} Stride, p 16.