has set in. Put them in a poly bag for a few days. When you open it, if it smells like ammonia, don't put them with your other dice. It could be the downfall of your other older dice. Also, try to keep them from moisture, which accelerates the decomposition process. Older dice are totally cool, but unlike diamonds, they aren't forever. Eventually they just disintegrate on their own.

Sorry if I'm the bearer of bad news.