I put mine in olive oil and it gets all the grime off of it, It works pretty well but I'am sure that some of the professionals here should be able to help you, HH CS
I was told this by a former coin dealer, ( he ended up finding God, just kidding). He told me to get some fingernail polish remover the non-acahol type and use a cotton ball. Try it on some non valuable ones first and see what you think.