bone. You can see the veins where the blood vessels used to be.
edit:
Errr......
Uh.....
One side definitely looks to be bone, but the other side also appears to be ivory. Perhaps an ivory scale broke and was replaced by bone?
Yeah. Thats my current working theory.
good eye...i was confused by that too. the show side has these dark pits consistent with bone, but the rear side has the wood grain to it indicative of ivory...but if it is a replacement (agree that it is more likely that both were ivory and then one replaced by bone), that's some pretty decent replication wrt width, length and THICKNESS.
Ivory feels like ivory, doesn't feel like bone; but it does feel similar. Words cannot describe the silky smooth feel and cool to the touchness.
So the side that looks like ivory in the pics feels like ivory and the side that has the veins feels like bone? Sounds like confirmation. You sir, have ivory.