I just boil them in water, but not too long, maybe 2 or 3 hours. Over cooking will cause the bones to soften and get gray and separate. Then I take it to the car wash. I have done this on many skulls. Be careful with the nose piece, but if you didn't over cook it should be all right. Then I usually hang it in a tree in the sun to dry. You might have a few small pieces of meat to pick out.