Yep....not uncommon at all for these types of jetons. As David said, once it happens, there's nothinhg that I know of that stops it. I've tried all sorts of cleaners and baths with no success. Not that I have tried everything....There very well may be something that can nutralize it but I've not found it.

The problem seems to come from lake of air. I just keep all of mine all together in a little box with no lid. My experience is that when there is air circulation, even slight, all seems to be fine. There has been no collateral damage to the other jetons even though they are touching.

I have always thought these jetons would be a perfect choice to make a wall display with a chipboard with no glass.