sintered or toned?

[drewbaccas]

If neither then what is it?

 

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[huntsman53]

Probably some type of contaminants or possibly mold! I have seen many coins like your's that were stored in a large Coin Albums and kept in locations where the Albums drew moisture. Most of the coins in these Albums were toast. You might try a bath in Acetone to see if it will remove whatever it is. If it does, then give the coin a light bath in a dishwashing liquid and water mix, rinse, then pat dry between the folds of a soft towel. Acetone is great for removing stuff like that as well as Verdigris from a coin but you don't want it to stay on the coin very long as it can do some real damage to it.


Frank