I boiled the head of a deer I shot this year. Used Dawn dish soap. Got it clean pretty easy. Ordered some 40% peroxide off amazon that took a couple weeks to show up. While I was waiting the skull started turning a bright yellow in spots. Applied the peroxide and it whitened it up nice. Now a few weeks later the yellow is coming back. Any advise to get it to stay white?

My thought is when boiling it can cause the fat to leach deeper into the bone and is now coming back out. The beetle cleaned skulls I sell I usually soak in dawn and water for several days before whitening them. Or several weeks if it is a hog skull. Using a bucket heater or aquarium heater in the dawn mixture can speed the degreasing, but since I do this to help cover the cost of my leases, I don't want to spend more money on electricity than the profit I make selling the skulls so I usually just give it more days pouring the grease off the top and extra dawn/water changes. Some people will also soak them in acetone to degrease them for much faster and I am sure better results and is probably what I should be doing with my hog skulls.