Asked in Coins and Paper Money
What year did US dimes and quarters begin using copper as a filler?
Copper has never been used as a "filler". U.S. silver coins dated 1964 and earlier are made of an alloy containing 10% copper and 90% silver. Copper is necessary to harden the coins to prevent excessive wear. By itself silver is so soft that the coins would have worn out so quickly as to be impractical for daily use.