Thank you for the welcome! Yeah, it seemed odd to me. I didn't notice any bubbling from heat so figured I would throw it out there to see if anyone saw something similar. I'm new to this game.
I will admit to a habit of baking copper-coated zinc cents (Zincolns)...under the heating element of an electric oven, heated to 450 degrees and taken out when it came to temperature
Your coin has little wear and I do believe that repeated exposer to high temperatures would give it that black oxidized look/color.
I will go with Sulphur experimenting attempt followed by dip experimenting. I would think, though, that a fedcop would have run this by forensics analysis for evidence and conclusion. Don't hit me. My mind wanders.
This is one instance when photos of the edge might help. Looks like just ED, environmental damage to me.
