[] Clear coating old Cellulose Nitrate dice that are starting to crystalize will help extend their lifespan, as well as make them safer to handle without damaging them.
[] More modern dice are made from cellulose Acetate, hence the vinegar smell when they start to break down and the acetic acid leaches out. Best thing to do with dice that have "vinegar syndrome" is to quarantine them from your other dice, and store away from heat and sunlight.