Scrimshawed by sailors of old. Color is a yellowish cream. Prehistoric Walrus ivory is seen in the current marketplace. There are apparently characteristics in larger pieces of this ivory that may allow precise identification as walrus. Most of these will have lines that are too straight, too even, and will continue down the ends and on the other side with no variation.
Bone has tiny little channels where the blood vessels and nerves resided.
Corozo nut and also the doum-palm nut. Grandpa Spragg has a wonderful information page about the Tagua nut and examples of his carving. The characteristics are the sam as hippo ivory and separation of the materials is difficult. I have seen bone or other materials that were lightly brushed with a sienna color dye, giving an impression of patina and simulating, but not closely, the grain of ivory. The difference in translucence in the layers of lines will often show up under these conditions.