my old page on the topic:

HOW TO DISTINGUISH BETWEEN (1) BONE, (2) IVORY, AND (3) CELLULOID ("FRENCH IVORY," A PLASTIC)

http://www.antiquegamblingchips.com/distinguish_iv_bon_cel.htm

Note: a good some of the time I have trouble distinguishing ivory v. polished bone and plastic. Often the ivory grain is not so apparent.

Josephine page:
http://www.antiquegamblingchips.com/Ivories_Josephine.htm

Robert