This was sitting in a pawn shop for quite a while, got it for a good price. I believe that I know what the net grade is.(having it in hand), What would be your grade? It came in a lot worse shape than this, it was corrode with something acidic. . I saw that it had a good patina to it, but, the cleaning was obscured by the corrosion. It got an acetone bath, and a queue tip. If I am missing the reason for the problem coin, please give your assessment.
I'd be surprised if acetone would have any effect on it at all. Acetone is useful for removing crud and gunk. It will not have an effect on toning.
If acetone dont lighten some of that black try like olive oil or even verdicare. I've not tried it on silver but copper or bronze I've had "some" luck. The corrosion isn't going anywhere but may lighted up a little. If all that fail try a dip.
I think I will plan on leaving it in the condition that it is. Its a hole filler until another comes around.
