I use a lot of mammoth ivory. Some from Rick Fields. He's a very good supplier with superior merchandise. Not cheap, but good stuff.
Couple of ivory handled knives on my webpage, both of which have Rick's ivory. Take a look:
http://www.livingston.net/mayor
Some tips: Wear a GOOD respirator, not one of those little paper disposables, either. Stuff will make you really sick if inhaled.
Work with a good sharp belt. Heat will scorch it and ruin the piece. Dull belts build up heat much worse than new ones.
Keep it dry. It often comes from the supplier pretty wet. A few weeks in a drying cabinet, or in your hvac chase behind the filter is a good idea. Don't even think about dunking it in the water bucket while grinding. It has a high shrink/swell tendency.
It also has a tendency to check or split along the long axis, particularly if it is installed wet and shrinks. Keep any pins or thongholes well away from the ends of the scales.
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Ben R. Ogletree, Jr.