Cleaning Question

The first rule of coin collecting is: Don't clean coins.
I believe it is also the second rule.

Having said that, If the coins are near worthless as they are, and you paid only $2 for the lot, you have very little to lose in trying to make them look nicer. the dime coins between 1946 and 1964 are silver, but don't use silver polish! I'm not sure how to clean up Silver to get mold off and not the tone of the coin. Hopefully others will have had more experiance with this and post.

I would recommend dipping them in acetone. This will not harm the metal and it should lift the black residue right off. You can leave them soak for a little while. Use pure acetone, not nail polish remover which has additional ingredients. You should be able to get this at any hardware store cheap. Make sure the area is well-ventilated as the fumes are very strong.

I figure a coin becomes damaged immediately after it is cleaned. I have some silver quarters and dimes with black stuff on them but I left them as is.

Organic solvents (like vodka, rubbing alcohol, methanol, acetone, petrol, etc) are non-acidic and do no harm to metallic surfaces. They won't remove corrosion, oxidation or tarnish, either. All they remove is "organic gunk", like the green goo from PVC plastic, stickytape residue, paint, etc and they should do a good job at removing mould. Soap and water should also do just as good a job.

Note: not all those substances listed above are recommended for coin cleaning, as some (particularly the less chemically pure ones, like petrol and vodka) may leave a thin film of impurities on the coin once the solvent evaporates.