The soft green stuff that grows on coins is a reaction between the silver/copper in the coin and the plasticizer in the soft plastic holder. I've always been able to remove it with a solvent.

What you see on the FM tokens in the scan is hard corrosion, probably either copper sulfate or copper oxide. It's a result of undesirable compounds in the thick cardboard holder that FM used, and usually a little moisture. Dipping and solvents don't help. As a last resort, I've even tried scraping it off with a knife; doesn't disappear unless you start scraping off the token surface itself.