A Question About an Un-Plated Lincoln Cent

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Author: Bill O'Rourke

I found a penny (cent) dated 1991 D that should have the copper plating on it. This one seems to have the plating missing. Did I find a valuable coin?

Part way through 1982, The United States Mint changed the composition of cents to a copper-plated zinc. The core of the coin is composed of 98.2% zinc and 0.8% copper. The core is plated with pure copper. While it is possible for a coin before it was struck (in this case the blank) to have missed the process that involves the copper plating, it does not happen too often. For the production of cents, the Mint purchases the blanks that are manufactured by outside sources. The Mint however, does supply the outside sources with the zinc and the copper used for the manufacture of the blanks. It is unusual for the blanks to arrive at the Mint without having been plated.

Many science experiments in middle schools and high schools involve the removal of copper from the copper-plated zinc composition cents. Some experiments involve the use of nitric acid on the surface of the coin. The nitric acid will remove the layer of copper from the zinc core. Because there is some copper in the zinc core, the core will also be effected with the result being a slightly rough surface appearing on the coin. The nitric acid does not effect the zinc.

Your coin also exhibits remnants of the copper on the surface and on the edges that indicate that the copper that was once on the coin had been removed.

I placed a picture of your coin next to a genuine coin that missed the plating process. You can see the rough surface on the 1991 D dated coin as opposed to the smooth undamaged surface of the 1987 D dated coin.

Since your coin has been damaged by acid, it does not have any numismatic value.