You can also use magnesium carbonate and your peroxide and do the same method as clindsayrun said, make a thick paste, put it all over the skull and let it dry, the directions say to at least let it dry for 24 hrs, the longer the better, when its dry just peel off the hard white stuff, it will come off in clumps and the rest you can just brush off or rinse. You can order magnesium carbonate from Research Mannikins for pretty cheap, around $20 for 5 pounds and a little goes a long ways and when you order from them it comes within 1-3 days.