There is black stuff (organic matter) which might be able to be removed with acetone and not adversely affect the appearance, and there is black stuff (silver sulfide) which is the "natural" toning/tarnishing, and will probably make the coin look cleaned if you try to remove it.
It's hard to tell from the photos which you have more of.
Green can also be some kind of organic residue from vinyl, or can be verdigris, a copper compound.
Edited by tdziemia
07/02/2020 07:52 am