I've got two skulls, a gemsbock and a warthog, from my Namibia trip in 2008 that I just can't seem to get dried and whitened. The warthog in particular continues to have yellow unbleached areas that are somewhat tacky to the touch. I've tried soaking them in hydrogen peroxide for days on end, a bleach compound from a beauty salon, and even the Cabela's european mounting kit but none of these have made a difference. Has anyone else had this problem and what else can I try to make them white and dry?

The problem is grease. The teeth should be pulled to clean out the nerve cavity, then you need to soak it in something to cut the grease before soaking in peroxide.

Acetone works best, but it VERY flammable and toxic to work with, harder to get in large jugs.

I've had luck with coleman's camp fuel( white gas), removing grease from a bear skull that was very yellow with grease. Try and find a 2.5 or 5 gallon pail with a lid, (whichever one fits the skull) and cover with the white gas. put on the lid and let it sit for a few days in a cool place outside or in the garage. The fumes will soften/eat the rubbery seal ring in the lid.
Check it after a few days, the grease will be laying in the bottom of the pail. Let the skull dry in the sun, before it goes in the peroxide.
You can pour off the gas and reuse for the same purpose, just watch the seal on the lid.
I hope you find this useful.

Thanks for the help, I'll give these a try.

Place the skull in warm water--not boiling-- on the stove and let in sit in the water w/ dawn soap and it will be degreased in that way and then place it in the whiteing agents. It takes a little time but you want the water warm enought to melt grease.......

Lacquer thinner for 2 weeks then peroxide

or

1 gal water + 1 cup amonia + 1 cup Dawn dish soap clear + 1/2 cup peroxide 40% heat water to 120 degrees with a bucket heater. this will take a few weeks to months but will work eventually