Well, scrimshaw, while practiced on ivory, as noded above, is also practiced on bone.
Just a little about the origin of scrimshaw.
It was practiced for centuries by the Inuit and other native groups along the Northwest Coast of North America. The Yankee whalers adopted the practice in the early 1800's. Since some of the voyages lasted anywhere between two to five years, boredom and monotony set in. The whalers turned to working with baleen, whale teeth and jawbones, all of which were in abundant supply, to relieve the situation. On many of the ships, whale teeth were part of the sailors pay. They were often traded to shopkeepers in port for goods and services. Some of the more popular scrimshaw subjects were whaling scenes, the ships, women, and scenes copied from magazines of the times.
The origin of the word "scrimshaw" is somewhat obscure although one interesting etymology is a Dutch phrase that means "to waste one's time".
Now a little about the care and cleaning and treatment of your treasured piece of scrimshaw.
Just like any other piece of fine jewelry, try not to get your scrimshaw wet. This causes the inks that were used, especially the colored ones, to fade. Keep it out the bright sun since this might dry and crack the ivory and also contributes to the fading of colored inks. Avoid using detergents, shampoo's heavily chlorinated water and jewelry cleaning solutions, they turn the ivory surface dull and might removed some of the etched lines. Any accumulated dirt and oils should be removed with a cotton swab moistened in rubbing alcohol and rubbed ever so gently over the surface. Scrubbing will remove the ink in some of the finer lines. A warm coat of beeswax can be rubbed into the ivory to preserve the scrimshaw and keep the ivory from drying and aging to quickly. The beeswax should be re-applied after each cleaning because the application of rubbing alcohol removes it.
If you're still with me, and, for some of the more environmentally conscious folks, the following is some of the more popular materials used in scrimshaw that can be legally obtained and do not endanger any living species.
Naturally shed deer, elk and moose antlers
These are used for more unique type pieces and desk accessories such as pen bases, letter openers with fine blades and antlers as the handles, key rings, fireplace sets and cribbage boards. They are also used for knife scales and handles that get a lot of wear because they are tougher than ivory.
Recycled Piano Keys
Actually I guess you can call that "recycled" elephant ivory. The shades range from bright white to a yellowish brown. The pieces are thin, usually less than 1/16th of an inch and might have a wood like grain. Some of your more popular pieces might be bookmarks and sewing rulers.
Fossil Walrus Ivory
These are either the teeth that are periodically shed by the walrus and washed ashore, or tusk pieces. The tusks can be in the form of artifacts taken from old Eskimo village or fresh ivory taken legally by the Eskimos and distributed by the local Fish and Game Commission.
Mammoth or Mastodon Ivory
Pretty hard stuff to come by and is usually not found in pieces that are large enough for scrimshaw. However, if your lucky enough to come across some, its usually means that its either from Alaska or Siberia and his been in a glacier and preserved by the cold. Some of this ivory is at least 10,000 years old.
Last but not least, and again, for the environmentally conscious, avoid whale ivory. This is because the Marine Mammal Protection Act of 1972 and Endangered Species Act of 1973 has severely limited its trade.