These were discovered with some hoarded belongings my father-in-law had. Is this oxidation of some sort? Or just abused? I cannot read dates for the 2 coins on the left. Is there a way to remove this?
You could call it oxidation if you want. Corrosion would be a better term. It falls under the umbrella of environmental damage, regardless. I'm afraid here's not much you could do to help these that would reverse the damage and wouldn't just end up making them even uglier. Better to leave the "old ugly" than make them "new ugly". "Old ugly" is at least slightly more interesting. I deleted your second, identical thread about these same coins.
If you look up NiO ( Nickel oxide), the color is a close match to the coins, maybe a little nickel hydroxide mixed in.
