Degreasing 101- Three Ways to Turn Yellow Bones White

What is Degreasing?

In terms of cleaning bones, degreasing is the process of removing the natural oils and fats from bones so they are no longer yellow, translucent, or waxy feeling.

What Materials are Needed to Degrease Bones?

1. Flesh-free bones (see Maceration 101 if your bones aren’t flesh-free yet)

2. A waterproof and/or acetone-safe container that can be sealed

3. At least one of the following:

4. Recommended: Aquarium Heater or Bucket Heater

5. Recommended: Strainer to not lose bones

6. Acetone-safe Respirator and Gloves

7. Water

8. Recommended: Mesh Bags

Click Here to See a Full list of Supplies I Use to Process and Articulate Bones with Reviews of Each of Them

Why/When to Degrease Bones

Grease in bones can cause them to be sticky, discolored, or smelly. If your bones are displaying any of those signs, you likely need to degrease them. Grease can be noticed in bones by them being translucent (almost making the bone look wet), or it can be an array of colors including yellow, orange, brown, and various shades in between. 

This is a red fox skull that needs to be degreased. The majority of the skull is white and degreased, but these two sections near the back molars show a lot of grease.

You will never be able to have a white, clean skull if it has grease in it. Some grease can be seen on the surface of the bone, and other grease can be deep within the bone and not be visible for months until it surfaces. This is why it is important to not put any coating on bones (including paint) until they are completely degreased. Deep grease can surface later, showing up trapped under lacquer or messing up paint.

How Long Does Degreasing Take?

This is the question I hear the most, and the simple answer is, it takes however long it takes. Degreasing is almost always the longest step of processing animals, and there is no quick way of doing it without damaging the bone (we’ll cover why not to boil/simmer bones in peroxide or oxyclean to “degrease” them at a later time.) Some lean animals (often young animals) occasionally do not need to be degreased at all. Others like bear, boar, elephant feet (personal experience), and other fatty animals can take many many months to finish degreasing. In my personal experience, cats usually take about a month to degrease, and dogs can take 1-4 months depending on the breed and how fat they were. These time frames are just an average of what I’ve dealt with. Some may take a week, others may take 6+ months. It really just depends on the animal.

Degreasing Method 1: Soap and Water

Arguably the easiest and cheapest method of degreasing involves some water, dish soap (Dawn recommended), and heat (recommended.) This is the method that most beginners will use at first, as the materials are easy to find around your house. All you need to do is mix some Dawn (For my international readers: Dawn is a name brand of dish soap in the US. “Fairy Liquid” is another name for it overseas- just find a dish soap that removes oils) with water (there’s no set ratio of dawn to water, just make it bubbly), place your bones in, and keep it hot. There are several ways to keep the container hot, such as using a heater– link to the one I recommend for 5gal buckets. The heater is a bit pricey ($50-60), but they last a very long time (I never had one burn out) and work very well. Ideally you want the temperature anywhere between 80-115F (26.6-46C) If you forget that the thermostat is in Celcius and accidentally set it to 80-115C you will melt your bucket and potentially start a fire.), aquarium heater (you’ll have to bypass the temperature controls to get it hot enough), placing the container outside on a hot day, or placing the container near something that will keep it warm. Different animals’ fats break down at different temperatures, but keeping it around or below 115F (46C) will cover most fats. 115F is not too hot for bones (we will cover the effects of higher temperatures in another article), but if you’re not able to get it quite that hot it’ll still work. Room temperature is not recommended for the dish soap method, as heat will thin the grease and speed up the process. It’ll still work at room temperature, it’ll just be much slower.

Clear dawn is best to use, as it will allow you to see the bones better, easily show if yellow grease is coming out, and you have a 0% chance of staining the bones. I know several people who have ended up with blue bones from using blue Dawn to degrease. You may also use other brands of soap, though Dawn is known as one of the better dish soaps to use. Avoid using detergent of any kind (including borax, baking soda, oxyclean, or anything similar) as they are not effective degreasers or can damage the bone.

When your soap water mixture turns cloudy or yellow, its time to change it out (roughly once a week.) Simply pour it out, wash off the bones, and refill with fresh Dawn and water. Repeat the process until the bones no longer appear greasy.

Degreasing Method 2: Ammonia

This method is very similar to the dish soap method, this one just uses ammonia instead of Dawn. I personally have used this method the past several years, and it works very well. You can use concentrated ammonia from a hardware store (usually 10-30%) or very diluted clear household cleaning ammonia from Walmart or a dollar store that is 2.5% strength (doesn’t say the percentage on it- I had to look it up). If you’re using the concentrated stuff you can use it straight or dilute it. I used to use the cheap 2.5% stuff from Walmart, and then dilute it even more. Now I buy the 10% concentrated ammonia from Ace Hardware and dilute it down to 2.5%. Rough ratio I use is a half gallon of 2.5% ammonia to 10 gallons of water. Buying it from Ace saves a few dollars and keeps you from having a million half-gallon jugs lying around. The fumes from the 10% are extremely strong, so make sure to use a respirator with a shield to cover your eyes. Supposedly you can use the strong stuff without heating it, but I personally use the diluted and then heat it to 112F (44C) with a heater– If you forget that the thermostat on this heater is in Celcius and accidentally set it to 80-115C you will melt your bucket and potentially start a fire.) Make sure not to use the lemon scented ammonia! It can stain bones, and is very hard to tell when it’s time to dump it. Use the same steps as the dish soap- change it out when it gets cloudy, yellow, or when grease is floating on top (I change my degreasing buckets once a week.)

Use caution when using ammonia as it very easily irritates your nose and eyes. Try not to breathe in the fumes, as it will take your breath away (but open up your sinuses!) Ammonia is used to wake up people that pass out- the stuff smells STRONG. The fumes from the 10% are extremely extremely strong, so make sure to use a respirator with a shield to cover your eyes. If you’re using the 2.5% ammonia you can wear a respirator (without the face shield) if you’d like, but the fumes aren’t near as strong as the 10%, and don’t have negative health effects like acetone does.

Sometimes you'll find this- the water appears clear, but there are literal oils floating on the surface. Still time to change out the liquid.
This is after degreasing in heated ammonia for one week. The ammonia water was clear when I put it in. This means the bones are extremely greasy, but the degreasing process is working very well.

Degreasing Method 3: Acetone

This is the most expensive, but least labor intensive method. This is not a method for beginners, as special equipment is needed to work with acetone, and it has negative health effects and is a safety hazard. You will need airtight acetone-safe containers to keep the acetone in. Acetone dissolves many plastics, so you’re safest using glass containers. If you’re using a plastic container, make sure that it says HDPE on the bottom-  HDPE plastic is acetone-safe. The container has to be airtight, as acetone evaporates very very easily. You’ll also need acetone-safe gloves (Butyl Gloves are the most common) and a respirator for organic vapors. Regular nitrile or latex gloves will quickly fall apart when exposed to acetone. Acetone will dry out your skin, and is not good to breathe. It’s also extremely flammable, so it will need to be kept in a cool place, far far away from any source of heat or spark. The fumes travel easily and can very easily ignite with a small spark. Only work with acetone in a very ventilated space.

Now that the safety aspect is covered, we can move on to the usage. Using acetone to degrease bones is very simple. Simply place the bones in it and wait.  You cannot dilute acetone, and at roughly $14.65 a gallon (at Walmart) it makes it quite expensive to use to degrease larger things. Do not heat the acetone, it works just fine at room temperature. Acetone does not need to be changed out near as often as the other two methods, as it can be reused many many times until it turns a dark orange color, at which point it will no longer dissolve any grease. I usually have to retire acetone after about 3-5 months of use.

Huge elephant foot and cassowary leg bone (both zoo animals that I was working on) in 7 gallons of acetone. The foot took over 5 months to fully degrease.

Another negative part of using acetone is you cannot pour it down your drain like you can Dawn or ammonia. Acetone needs to be taken to a proper disposal place (places that accept grey water usually accept it), so you’ll have to find a place near you to dispose of it when you’re done using it. Make sure to let any bones that were in acetone COMPLETELY DRY before whitening them. Acetone reacts very violently with peroxide, so make sure they never come in contact with each other.

Which Method is Best?

There is really no superior degreasing method. I personally use heated diluted ammonia or acetone (not heated), but many many people swear by the Dawn method, which also works! Experiment with different methods and see which one you prefer. Acetone doesn’t need to be heated like the others, but is also dangerous to work with and requires special equipment. There’s also many other methods of degreasing that are not covered in this article (such as using horse manure to degrease bones!) I simply wrote about the three that I have experience using.

Tips and Tricks

Degreasing takes forever, there’s no getting around that, but there are a few things that you can do to slightly reduce the degreasing time. 

  1. The first of which is to not rush maceration! Macerating bones drastically helps in comparison to beetling bones. Maceration bacteria begin to degrease the bones inside as the flesh is being eaten away on the outside, whereas beetled bones are usually very greasy from the fats drying and oils soaking into the bones while the beetles eat the meat on the outside. Leaving the bones in maceration for an extra week won’t hurt anything, and can actually cut down on degreasing time by eating away the fatty marrow inside the bones.                                                             
  2. Drill small holes in the long bones (leg and arm bones) for the marrow to get out! There are two types of bone marrow- red and yellow. Red marrow is where the majority of your blood cells are made, and yellow marrow is where a lot of fat is stored. If the marrow does not come out of the bones and ends up drying, it can lead to them looking dark or greasy. Macerating and degreasing usually eats all of it without drilling, but drilling a small hole in each side of the bone drastically helps get it out. If you’ll drill the holes in a freshly macerated bone and then run water in one side you can literally see the liquefied marrow run out. So it’s not a necessary step, but in my experience it helps. Just drill the holes in hidden spots, or where you plan on having a drill hole anyway if you plan on articulating.                                                                                                  
  3. Cycling between degreasing and whitening! I personally cycle between ammonia, peroxide, and acetone to help degrease super greasy animals. I’ll do a few weeks of degreasing in ammonia, let the bones completely dry, put them in peroxide for a few days (Read our Whitening Guide if you haven’t already), let the bones completely dry, degrease in acetone for a few weeks, let them dry, rewhiten, let dry, repeat. After the bones dry after a peroxide bath it’s much easier to spot any leftover grease. I also think cycling ammonia (or Dawn) and acetone works really well as ammonia and Dawn thin the grease, making it easier for the acetone to dissolve it. Just make sure to let the bones COMPLETELY DRY between baths. As I said earlier, acetone and peroxide do NOT mix well together.                                                                                                                                  
  4. You can keep your bones in Mesh Bags to make sure you don’t lose any bones, and so you’re able to degrease multiple animals in one container- saving space and chemicals! I personally have several hundred of these bags, and I LOVE this company. The bags have a lifetime warranty, so if any stitching comes undone, just send them an email and they’ll send you some new ones. I’ve actually spent so much money on these bags that the company decided to Sponsor me and give me a small portion of all sales that come from this blog! So if you want any mesh bags (small, medium, or large- I use all of them) and want to help me afford my unhealthy obsession with buying more bags, please use the link above to purchase any!

What Do I Do Now?

Well, if you’re happy with your degreased bones, you don’t have to do anything else! If you’d like to whiten your bones, you can move to the next guide, Whitening 101,  if you’d like, but that is not required if you’re happy with the natural color of the bone.

If you found this article helpful, feel free to leave a comment down below or share it with your friends! I don’t get anything directly from making these guides, but it saves me time answering questions and helps you all so I’ll continue to do it! I don’t ask for/accept donations, but feel free to grab something small from my Shop or follow me on my social media (InstagramFacebook, or Tumblr) if you’d like to support my work!

If you noticed any typos while reading this, any links don’t work, or have any suggestions or questions that weren’t covered in this article or the other articles on my Blog, please leave a comment below or Contact Me

I’d like to give a very special thanks to Suzy G. for letting me use the before and after picture of her Opossum skull in this article. You can visit her etsy store by clicking here.

Here's a before and after of an opossum skull that was degreased by cycling acetone and dishsoap. Very special thanks to Suzy G. for allowing me to use this picture of hers!

3 Responses to “Degreasing 101- Three Ways to Turn Yellow Bones White

  • very helpful + very well-written, thanks!

  • I think you did a great job covering a large amount of information I’ve been hard pressed to find thus far. One question, you touched on minimally young skulls vs adults…i have a young goat skull which you stated may not require decreasing methods that adults require. Could you please elaborate on that and how i can be sure since ive already began encrusting my skull in amethyst. Thank you!!

    • Hey, Holly,

      Young animals usually are not as greasy as adults. After you’re done macerating and whitening it if there’s no signs of grease (yellowing, translucent spots, etc) then the skull may not require additional degreasing

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