Here is a Wostenholm in celluloid, made to look like ivory. Too thick, lines too even, no depth, collars on pins:
http://i76.photobucket.com/albums/j2...mCelluloid.jpg
Here is bone, a Case Bradford. Nice, but textured rather than smooth surface, slightly thicker and more rounded than ivory, brown pores prominent toward ends, no ivory "glow" or depth. Collars on pins (although I have seen a few bone scales pinned without collars):
http://i76.photobucket.com/albums/j2...D/CaseBone.jpg
Mappin & Webb in elephant ivory. Thin, smooth, depth, figure, and the pearlescent, almost translucent toothy "glow". Pins with no collars:
http://i76.photobucket.com/albums/j2...dWebbIvory.jpg