Copper-Plated Zinc Cents

Lincoln cents made from late 1982 to now have a zinc core and are plated with a thin layer of copper. Minting errors, as well as damage, may leave the zinc exposed and a layer of hydrozincite is formed over the exposed area. As a coin circulates, this protective layer is removed and forms again, repeated exposure, reaction, removal lead to the increase of the affected area, until eventually, the coin may no longer be recognizable as a coin.