I had 2 skulls and I placed them in water for approx. 5 weeks. I then pulled them out and simmered with sal soda to remove any residual flesh. The skulls were extremely yellow, almost like a yellow orange. I never degreased them (probably should have) and then mixed basic white and 40% peroxide. The only thing that whitened on them were the teeth, the yellow is still their. Should I try to degrease them and with what? What do I do next? Any help would be greatly appreciated.