That is a pretty substantial strikethrough. It must be copper because a Zincoln only has a very, very thin coating of copper. ~ Chris
Chris I believe the op where he said the coin is copper. On a struck thru copper or copper plating would not make much difference because none of the plating was removed.
But for something as large and deep as that, there would be a possibility that the plating would split. You can see this in many broadstruck and off center cents were the metal flow causes the plating to stretch to the point of failure. It doesn't take much to split the plating. I'm not saying that splitting absolutely would have occurred with this specific example if it was a zinc cent, but the impression is deep.
Look at this coin. The date is unknown due to the strike through. But it's a LMC so it between 1959 and 1982. It's all copper and that's easy to tell.
