Celluloids are a class of compounds created from nitrocellulose and camphor, with added dyes and other agents.
Generally considered the first thermoplastic, it was first created as Parkesine in 1856[1] and as Xylonite in 1869,
before being registered as Celluloid in 1870.
Celluloid is easily molded and shaped, and it was first widely used as an ivory replacement.
source: Wikipedia

[0654 x2] A pair of celluloid D6's with a brass cup from the Monte Carlo casino, 16 mm.

[0655 x2] A pair of celluloid D6's, 17 mm.

[0656] Celluloid D6, 15.7 mm.

[0827] Celluloid (possibly ivory) "Put and Take" die, 15.2 mm.

[1165 x2] A pair of celluloid D6's, 15 mm.

[1166] Nice celluloid D6 with bird's eye pips, possibly used in a casino, 17.5 mm.

[1225 x5] Old celluloid poker dice, UK, 14.6 mm.

[1248 x2] Two very old rather small poker dice from around 1873, celluloid, 14 mm.

One die dissolved over time; here the remainders...

[1284 x2] Two old celluloid dice, 16.2 / 16.8 mm.