I don't know for sure, you could contact an ivory guy for a definitive answer.
If I was doing it on my own stuff and had no source for information I would use naphtha for cleaning, lighter fluid, and olive oil or mineral oil for re-hydration then after its stable I would use a sealer like Tru-Oil by Birchwood Casey, thats just an opinion but I cant see how any of that stuff could hurt it, its all proven safe for sensitive finishes and natural fibers.