When did copper clad coins start?

Answer 1

1965, but they're actually copper-nickel clad. Dimes and quarters were changed in that year, but halves took few more years to make the full transition.

When the price of silver started to increase in the early 1960s coins started to disappear from circulation because they were worth more than face value to a metal dealer. For example, you could get $10 in quarters from a bank then turn around and sell them to a scrap dealer for $15 or $20.

The Mint experimented with all sorts of different substitute compositions but most wouldn't work in the electromechanical vending machines and coin sorters then in use. They finally came up with the clad "sandwich" composition that had almost the same electrical properties as silver. That avoided forcing businesses to replace millions of vending machines; only some of the most sensitive ones had to go.

Before 1964 half-dollars circulated almost as much as quarters, but someone at the Mint had the bright (NOT) idea of turning the denomination into a "premium" coin with a reduced silver percentage rather than cladding it as well. But as the price of silver kept going up all that did was encourage people to melt every half dollar they had. The Mint refused to clad halves until 1971, and by that time so many had disappeared into melting pots that the denomination effectively stopped circulating.