1900 Indian Cent Dirt Or Corrosion?

Have you tried soaking it in acetone?

I think that acetone removes foreign debris on the surface of the coin but doesn't affect the coin itself.
It's worth a try and this looks like a good candidate.

Acetone isn't considered improper cleaning. And I'm fine with using it on silver or gold. But with copper, don't leave it in too long. I've learned that one the hard way.

Also, I don't like how flat circulated copper looks after an acetone dip. In some cases flat is better than full of gunk or residue. But I'm always hesitant. This is entirely just my opinion. But I think old copper looks better with the oils it has accumulated from people. And acetone removes that.