The quote below is from Boone Trading Company @ the link provided by Science Guy in post # 649. I don't have a dog in the fight, but I'm providing the information for those who might want both sides of the issue.
"Some knife makers and scrimshanders use mineral oil to protect the ivory from shrinking or cracking due to dry climate or lack of humidity; this seems to work best with slabs and thin pieces. Place the unpolished slabs in mineral oil for several days, then remove, wipe off and store in a plastic bag until you're ready to use it; the ivory will absorb some oil and after being sanded and polished will allow even less moisture to escape thereby reducing the possibility of shrinking and cracking. Another technique for oiling ivory is to put the ivory in a double boiler pan (water in bottom pan) with enough mineral oil to cover the ivory slices and gradually increase the temperature of the ivory to the point where the ivory sends up tiny bubbles of air/moisture. Leave the pan on the stove for about eight hours, and raise the temperature if the bubbling stops, but the oil should not be boiling. After the eight hours turn off the heat and allow to cool, wipe off the oil and store until you are ready to use; the moisture in the ivory has been replaced with oil, you will not be able to see a difference. We do not recommend these oil soaking treatments for fossil ivory, as it can get an oil soaked look. Your natural skin oil rubbed on ivory will help turn the ivory yellow faster and give it that antique look."