I picked up a few broadstruck nickels today. They all appeared uncirculated. This coin caught my eye. At first I thought some foreign substance after minting while it was in the wild got on the coin. I looked with some magnification and now I wonder if this is a combo of die grease and metal from minting process that is now part of the coin. I have gently scratched at the metal on the edge with my fingernail and nothing happened. Should I soak in acetone and see what happens? Any way this happened during minting? Thanks
How attached is it? Fingernail loosen it. It might respond to a soak. But I tend not to adjust surfaces that are still mint. I only use mineral oil to remove grime on devices on circulation examples only. You might try a vertical soaking on just the blackened area? That way not the full coin may not be affected.