Appears as though the copper coating is gone. The rim is raised and present. Is this the zinc I'm seeing? What would cause this?
anybodies guess, sandpaper, steel wool, some kid in a boring classroom rubbing it around on his desk...
I agree. PMD. Since the rims are raised if someone were to rub it they would lose the copper. What does the side of the rims look like.
The copper coating is still visible from the sides. Only the copper from highest point of the rim is missing.