How to Degrease Bones

Degreasing is one of the most confusing and frustrating steps in cleaning and whitening animal bones. It isn’t always necessary but, if the bones are yellow, shiny, and stink, then you probably need to degrease them.

Need more help? Read my post on how to remove tissue and how to whiten animal bones.

What Is Degreasing?

Surprisingly, some bones can contain a lot of fat. This is because bones are actually little “factories” which produce blood cells in their marrow. Guess what marrow contains? Lots of fat!

Degreasing is a process in which you remove fat trapped inside animal bones. If you don’t degrease bones, the fat will eventually leak out of the bones and cause them to turn yellow. In some cases, the fat starts to go bad and will rot the bones (hence the bad smells!).

When Is Degreasing Necessary?

Much of the time, degreasing isn’t necessary. The same microbes which eat tissue (read how to remove tissue off of bones) will also eat fat in the bone.

However, there are some situations where degreasing is almost certain to be necessary:

1: You Boiled the Bones

As I explained in the post about removing tissue, you should never boil bones. There is a lot of fat in animal hide and tissue. This fat gets in the boil water, and then the fat gets absorbed into the bone. Once the fat is in the bone, it is very difficult to remove!

Check out all the gross yellow grase spots on this pig skull which was boiled.

Here’s the back of the skull after a few days of degreasing. Look at all those greasy spots!

2: Certain Types of Animals

Some animal bones are greasy by nature. These bones almost always need to be degreased or they will stink to high heaven. The list includes:

Bears
Opossums
Pigs and wild boars
Seals
Whales
Elephant feet
Young animals
Vertebrae

Check out how greasy this possum skull is! Unfortunately, the grease starting rotting and the skull stunk so badly it had to be thrown away.

Some professional taxidermists will use gasoline or camp-stove fuel to get the fat out of animal bones. However, these substances can be dangerous so I didn’t include them here. Below are the easiest and safest methods for degreasing bones.

Method 1: Soapy Water

This is by far the easiest and cheapest method of getting fat out of bones – especially for amateurs.

Dawn dish soap works really well. Don’t use powdered dishwashing detergent meant for machines. Also don’t try to use chemical degreasers, like stove degreaser. It will literally dissolve bones.

Steps:

Put the bones in a bucket with soapy water. Use lots of soap.
Let soak.
When the water starts turning murky or gets globs of grease floating on top of it, dump the water and start again.

Tip:

For degreasing to work, the water needs to be warm. Otherwise the fat won’t break down and be able to leach out of the bone. The ideal water temperature is around 80-115F (26.6-46C). To get the water to stay warm you can buy an aquarium heater and put it in the bucket with your bones. You can also get bucket heaters from farm supply stores.

See the little blob of fat?

Method 2: Ammonia

Ammonia is a great degreasing agent and has the benefit of being cheap. You can often find it in hardware stores. Just make sure that you get the clear ammonia and not one that is colored as it might have additives which can harm the bone.

Most ammonia in stores is 2.5% strength. This can be diluted to a ratio of ½ gallon of ammonia to 10 gallons of water. If you get 10% ammonia, then you’ll use a ratio of 1/2 quart of ammonia to 10 gallons of water.

The problem with using ammonia for degreasing is that it has strong fumes. You must do this outdoors! You also must wear a respirator mask AND eye protection. It is very dangerous to get ammonia in your eyes. So, even if you feel stupid wearing goggles, put them on!!!

Disposing of Ammonia:

Ammonia can *usually* be dumped down the sink or toilet. You can even dump ammonia out on your yard. It will probably kill any plants that it comes in contact with though, so be careful where you dump it.

The exception is if you have a septic system. In this case, don’t dump it down the drain, toilet, or on your yard. Ammonia could end up in the ground water and ultimately into your well. If you have a septic system, then it’s probably best to avoid using ammonia.

Method 3: Acetone

Acetone is also a great degreaser, but is probably too difficult for amateurs to work with. First off, acetone is expensive and harder to get. Paint thinner (which is mostly acetone) will work, but some paint thinners may contain additives which could harm the bone.

Acetone cannot be diluted. You have to soak the bones in straight-up acetone. That means you’ll need a lot of it for larger bones, so it can end up being very expensive. However, acetone can be reused: just skim/filter the fat out of it and reuse the acetone with your next greasy bones.

Another issue is that acetone is potentially dangerous. It should NOT be heated as it is highly flammable. It also produces noxious fumes which should not be breathed in. You must use acetone outdoors and while wearing a face respirator.

The biggest deal breaker with acetone is that you can’t dump it down the drain. It must be bottled and taken to a disposal facility. For me, this makes it too much of a pain to bother with.

IMPORTANT: Acetone and hydrogen peroxide do NOT mix. The combination can be EXPLOSIVE. If you use acetone on the bones, then you’ll want to wash the bones and completely dry them before you whiten them with hydrogen peroxide.

How Long Will Degreasing Take?

As I mentioned before, degreasing is the most frustrating part of cleaning bones. Really greasy animals like bears can take months to finish. My pig skull took 2 months of soaking in soapy water before the grease got out.

Even with the same type of animal the degreasing time can vary. For example, a bear which ate a really fatty diet might take longer to degrease than a bear which didn’t.

The degreasing time varies so much that professional taxidermists (the good ones at least) will never guarantee a skull mount will be finished by a certain time.

The best advice I can give you is this: Be patient. As the professionals say, “It’s done when it’s done.”

How Will You Know Degreasing Is Finished?

Here are signs degreasing is done:

The water stops getting murky when you soak the bone
There are no more yellow or shiny spots on the bone

One tip is this: If you aren’t sure whether the bone is fully degreased, do a soak in hydrogen peroxide. This will whiten the bone and allow you to see grease spots easier. Plus, you’ll be better able to tell whether the yellow spot is a dirt stain or grease stain.

Below are some before/after of degreased and whitened bones.

Here’s the pig skull after 2 months of degreasing and then whitening with hydrogen peroxide.