Got another one too. This penny looks like it’s unplated on the reverse side. Took a picture of the edge too to show the issue, as someone requested that last time. Thanks again for helping me learn.
1958 wheat cents were not plated they are made of bronze. What you see is plating done on the coin after it left the mint that is now chipping off. It is considered post mint damage.
Originally it was not plated but then after it left the Mint it was plated. Now, most of it was removed.