When asked about unusual US coin compositions, a numismatist might mention 75% pure three-cent silvers, steel cents, or war nickels. The strangest coin make-up, however, is also the most common: the three-layer clad planchets we find in today’s pocket change. This metal sandwich has two copper-nickel layers as the bread and a pure copper layer as the filling. No other nation minted three-layer coins like this, so why did we?
The answer lies with vending machines. Vending machines use electrical tests such as resistance to verify the genuineness of coins. As the United States transitioned from silver to base-metal coinage in the 1960s, engineers designed a coin blank with the same electrical signature as a 90% silver coin. That is, a cigarette machine designed to accept silver quarters would also take clad quarters.
Because the United States is friendlier towards business than most other nations, the Treasury chose to incur the cost of the transition instead of requiring the owner of that cigarette machine to make costly modifications. There are parallels in other countries, such as when Britain changed the threepence from a featherweight silver coin to a sturdy brass piece in 1937 to accommodate bus and trolley fare boxes. Most coin issuers, however, change compositions and leave it up to businesses to adapt and pay for the change.
Today’s vending machines still use electrical sensors. With no need to accommodate silver and with better electronics, Coinstar and other machines now reject the occasional silver coin they encounter. The legacy of those silver coins, however, still exists in the clad sandwich coins that handle our everyday business.
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