Posted on June 29, 2017 by Ron Guth

When coins come clinking out of the presses at the Mint, they are pristine. Copper coins are bright red, nickel coins are flashy silver-gray, gold coins are brilliant yellow, and silver coins are shimmering white. From the moment they are struck, and as soon as they hit the atmosphere, coins begin to react chemically with their environment. As part of the reaction process, colors of various hues begin to form on the surfaces of these coins – in numismatic terminology, this is [...]