Wouldnt a chemical eat away at it at like the features on the penny because I mean nothing is like eating away on it it's all the features are still there
Chemical stain could be soda, juice, even urine. It does not mean just acid, bleach, ammonia or any other corrosive chemical.
Actually it is a Mint error....the error is making these hideous Zincoln's in the first place. Abe probably saw his reflection in a mirror & threw up!
It's an interest looking coin but not worth any more than face value. PMD (Post mint damage) but I'd keep it as a conversational piece.