'Cellulose nitrate was used to make dice from the late 1860s until the mid twentieth century, and remains stable for decades. Nitric acid is released in a process called outgassing. The dice cleave, crumble, and then implode.'
Deception, Fate & Rotten Luck by Ricky Jay and Rosamond Purcell
Hi! There's a whole exhibit on these at the Museum of Jurassic Technology in Los Angeles if you wanna go see it. You might also be quoting the exhibit and I just don't remember the name