I know pennies are now made of a mix of different medals, because copper is too expensive, but when did they stop using 100% copper?
1982 was the last year for copper pennies. And the first year for the zinc pennies. They made both types that year, and the only way to tell them apart is by weight — the zinc pennies are lighter.
100% copper pennies were last minted by the US in 1857. These were large cents, about the size of the "golden" dollar coins. The Flying Eagle and Indian Cents from 1856 to 1864 were 88% copper and 12% nickel. Beginning in 1864 Indian Cents, and later Lincoln Cents, were minted in 95% copper and 5% tin, technically this is bronze.