Hi, A larger image of the obverse would be helpful. I've seen many coins that look like this but the causes can vary. A chemical could have reacted to the surface of the coin, thus cleaning it. Also, things like laquer or adhesive can get onto a coin changing the way a coin tones. If for example, many years ago, the obverse of the coin was in a folder and the original owner of the coin "scotch taped" the coin into the folder, it would fit the look of this coin. The reverse is not worn or covered with whatever this is and the obverse is only partly affected by whatever that material is. Often it is the residue from the glue used on clear tape. I Hope this helps, Bill
Was going to guess glue at first, but maybe someone was trying to gold leaf it. If so, you might have about $0.00001 worth of gold there
Looks like tape to me. As mentioned before people tape coins into folders if they keep falling out. It doesn't have solid boundries because the tape didn't stick to the "valleys" of the penny, only the higher parts have the discoloration. I might be wrong but i'm pretty sure that's the case.
