I received this 1988-P penny in change a few months ago, and it has been sitting in my safe ever since. The words "IN GOD WE TRUST" appear to be filled with excess zinc or copper plating, which mint grease may have caused. It could also be the workings of someone with too much time on their hands. The reverse looks fine. What do you think? If it's a genuine error, what's it worth?
When a coin is struck by a grease-filled die those elements (where the grease has filled the die) will not be fully struck or they may be missing entirely. A grease-filled die will not cause extra raised metal on the struck coin.
This is often caused when die chips/wear creates extra gaps. When the coin is struck the metal from the planchet expands into them to create additional features.
