I've only used really old, well seasoned walrus and some 60 year old hippo. I kept a bucket of ice water handy, and never ran it more than a few seconds without dunking it in the cold water bath...heating ivory is bad news any way you cut it, if you'll pardon the pun.
To tell you how bad ivory is about splitting, curling, etc. - when a hunter takes a hippo the first thing they do is wrap the tusks in duct tape and KEEP them wrapped- if you don't, they'll split in half and curl like a dried banana peel.
Elephant tusks are also treated with a band near the base to avoid splitting as it dries like seasoned wood.
They both worked well without stabilization, though when I do more it WILL be stabilized. It's just too expensive and rare a material to take those unnecessary chances with.