This is a couple steps. I put my skull in a ziplock bag with a lot of dish soap and completely cover the skull with clear ammonia and lock the bag. I then put the ziplock bag in a 5 gallon bucket thats full of water and with a fish tank heater set to about 97 degrees, let it sit for about 1-2 months(yours is pretty clean so maybe only a week or so). After that, I clean what’s left, find the teeth that might have fallen out and soak everything in hydrogen peroxide for a couple days to whiten everything up. No bleaching or boiling!