Were dimes ever all copper

Nope. Dimes were struck in 90% silver up to 1964, and in cupro-nickel after that date.

If you have a coin that appears to be all copper, there are 2 possibilities:

> More likely, it was plated or exposed to a chemical that changed its color. In that case it's a damaged coin and is only worth face value.

> If it's much thinner than a normal dime, it's what's called a lamination error. That happens when the outer cladding doesn't bond properly to the copper core and falls off. This error could retail for up to $10-15.