Cellulose nitrate was used to make dice from the late 1860s until the middle of the twentieth century, and the material remains stable for decades. Then, in a flash, they can dramatically decompose. Nitric acid is released in a process called outgassing. The dice cleave, crumble, and then implode.
From Dice: Deception, Fate & Rotten Luck by Ricky Jay and Rosamond Purcell, 2002.After reading that I immediately checked my box of D&D dice, which have been sitting on the shelf for years. They all seem to be intact.
Text and image via Sutured Infection.