PVC contains softeners that will seep out and attach to coins in the wrong plastic bags. It looks like a green slime or paste, or a grey shroud. This has been known for decades but, believe it or not coin supplies made with PVC containing plastic are still being sold, especially in central and Eastern Europe. Also, old hands use affected coin album pages to send coins in. This is fine in principle, as long as the receiver takes the coins out on receipt.
If you have coins with the infamous green slime or grey shroud, the only cleaning method I know of is to rub it off with soft cloth. Used baby clothes are perfect. It is necessary to take the sofener off the coin. Copper and bronze will react with the stuff, so your coins will lose detail. On copper-nickel coins, the grey shrod can become permanent iff left on too long. In addition, you can get welcome surprises. I bought a batch of affected Russian rubles. On cleaning, I found that over half were actually proof.
Peter
