I've been asked multiple times how I go about cleaning and preserving the skulls that I find so I've decided to put together a sort of FAQ/how-to regarding this subject. Please keep in mind that there is more than one "right" way to achieve things in the realm of taxidermy. This is just the way I do my skulls/bones.
You will need:
Plastic bag for picking up your treasure
A good sized flower pot
An ant hill (if possible)
Disposable plastic gloves
Nice sized metal pot kept solely for boiling skulls/bones
Plastic container for soaking the skull/bones in
Hydrogen peroxide 3%-7%
Small pokey thing for helping remove brain bits and other yuck
Super glue, tacky glue, or Elmer's glue for putting the teeth back in
Hokay. While out hiking, I've come across many different skulls/bones of animals in various stages of decomposition. The best ones are when nature has already done most of the work for you and it's already pretty clean. One of the drawbacks of finding them like this though is that there is a high chance that some of the teeth will have gone missing due to its bouncing around the great outdoors for some time.
When I find a critter that still has juicy bits attached to the skull/bones, I take it home and place it beneath an overturned flower pot situated strategically near an ant hill. I then stack several large heavy bricks/rocks on the flower pot to keep scavenging animals from stealing my smelly treasure away from me. The ant hill is valued because the ants will help the flesh removing process go quicker. If you can't find an anthill, don't fret. There will still be other bugs that will help out with this, it just might take a little while longer.
Once you are happy with the amount of flesh that has been eaten away from your bones, collect the bones (wear your plastic gloves!) into your metal boiling pot and GENTLY boil them for 20-40 minutes. Yes, I am aware that boiling is not good for bones and teeth but I like to be a hundred percent sure that any disease, parasite, or bacteria that these remains could be harboring is not passed onto me by my handling them. So I boil them albeit at a low boil. If there are crazy big bubbles happening while boiling, you have the heat TOO high. You want it at a simmer which is a boil with gentle surface motion on the water. Once the water has reached the boiling point, start the countdown and make sure there is always enough water in the pot to cover the skull/bones. A good 30-35 minutes of boiling for a medium sized skull (ie, raccoon, badger, fox) should ensure that even the threat of potential rabies virus is completely nullified.
When boiling, please keep in mind that very young or very small animal skulls/bones are highly likely to come apart. I do not boil my bird skulls for as long as I boil something like a raccoon skull for this reason. Other little things like voles and mice can be very tricky too. I had to completely (and painstakingly) reconstruct a vole skull that I boiled that came apart. Vole teeth are super small.
Which leads me to another point. Even if boiling a larger, older animal, you are still most likely going to have all or most of its teeth fall out on you. Be very careful to keep track of all these teeth during the cleaning process. You will get to play puzzle later and glue them all back into their rightful places in the skull and jaw.
Once the boiling is done, I take my hot pot of water and boiled bones out to the back porch and drain the water while being very careful to not pour any of the teeth out with the water. Once most of the water is out and the bones have cooled a little, I reach in and collect them all from the pot to place them in a plastic holding container of water. Make sure this water is room temperature or, better yet, slightly warm, NOT COLD. The big temperature change is hard on the bones and teeth and could lead to premature cracking. Leave them to soak in this water for three days. They might start getting smelly if you leave them in the plain water for much longer.
After three days, pour out the water out from your plastic holding container (making sure you keep expert track of all those teeth!). Sometimes I rinse everything here but it is not necessary to do so before pouring in the hydrogen peroxide. Just make sure you've gotten most if not all the water out. You can use the same plastic container for this. I use the bottom half of old milk jugs that have had the top cut off or other small plastic containers that I've fished out of our recycle bin, the key is using the right size container for your project so that you don't waste hydrogen peroxide.
The hydrogen peroxide helps to further disinfect the skull/bones and whitens them considerably. If you want to try to retain some of that natural bone color, leave them to soak in the hydrogen peroxide for only about three days. If you want them whiter, I recommend leaving them for 1-2 weeks depending on how dirty the bone was when you started out. Be sure the hydrogen peroxide completely covers your project so the whitening job is even. Do not use bleach for this as it is very damaging to the bone.
Once your bones have had their nice whitening soak, carefully rinse them all off with water and lay them out to dry. I use paper towels for this, just be sure not to leave it in an area where a curious pet might come up and get into them. Sometimes I even speed up the process by paper toweling each individual bone. I actually recommend this since it allows you to really make sure that all the dirt and leftover cartilage are properly removed before the drying process is complete.
Do you still have all the teeth? Once everything is dry (or sometimes before, depending on how impatient you are), you can start playing around with the teeth and finding out which ones fit where. While you can do this before everything is completely dried, I only recommend gluing things once it really is thoroughly dry and once you are completely sure you know where each tooth goes. Also, an advantage to using tacky glue or Elmer's glue rather than super glue is that if you mess up, it just takes some hot water to loosen up the teeth enough to pull out and correct your error.
At this point you should now have a nice clean skull or set of bones (or both!) that you can be proud of, learn from, and show off for years to come. A couple basic tips for skull care is to keep them out of direct/harsh sunlight and to always wash your hands before handling them since the oils from your skin can leech into the bone and discolor it after awhile.
If there's anything I might have missed or if you have additional questions about anything, just ask.