BONE DEGREASING INFORMATION

Before discussing bone degreasing, it is important to understand the components of bone and fat. Bone is made of a mineral called hydroxyapatite, which is calcium phosphate [Ca3(PO4)2]3Ca(OH)2. Collagen makes up a significant part of the bone matrix. Type 1 makes up to 90-95% of all collagen in bone (Eriksen, et al, 2009 and Shehata and Krap, 2024). By ratio, bone is about 70% inorganic, 5% water and 20-25% organics (90% type 1 collagen, 10% non-collagen proteins and organics) (Lambri et al, 2018 and Pang et al, 2021). The hydroxyapatite can be thought of as a rigid and hard, yet brittle, scaffolding for the collagen which provides flexibility and tensile strength. There are four relevant kinds of bone for this document. these are divided into two macroscopic types and two microscopic types. The two macroscopic types are cortical bone and cancellous bone. Cortical bone, which is dense, often thick, and found on the outside of most bones. Cancellous bone, which is found on the interior of bones and contains marrow. This is where much of the grease is found. The two microscopic types are woven bone and lamellar bone. These are separated by the orientation of collagen (Bosch et al., 2011). Woven bone has random collagen fibers and is disorganized. It contains more osteocytes and fewer lamellae. This is common in juveniles and fish. Lamellar bone, found in adult mammal bone, is more organized, contains more lamellae and parallel collagen fibers. It is stronger and more resistant to heat.

Most people understand that compromising the minerals in bone results in a poor product. Altering the collagen will change the bone mineral mechanics (Viguet-Carrin et al, 2005) possibly leading to brittle bone (Burton et al, 2014) or possibly flakey, powdery bone. This can occur chemically, enzymatically or with excess heat. Zdzieblik et al (2021) discuss the positive relationship between increased collagen peptides and bone mass in osteopenia and osteoporosis in postmenopausal women, further demonstrating the importance of this relationship. It is therefore imperative to shelter collagen as optimally as possible for the best results. For types of fat, how they break down and additional information on bone tissue please refer to Turner-Walker 2012.

When discussing problem areas such as the maxilla near the zygomatic joint or the dentary, it is likely that the grease itself isn’t much more resilient but that there is an increased volume of grease and dense bone is preventing degreasing agents from entering or products from leaving. This may not be the case if the skull has a thermal history altering the triglycerides. It is possible that, with sufficient time and degreasing agents, the grease becomes entirely saponified. To test this, diabetes needles were used on a marten skull to access the dentary via the mental foramen and injected with degreaser. The maxillae were injected on the dorsal surface of the maxillary zygomatic process, directly into a pocket of “stubborn grease”. A tricky area around the basisphenoid was also injected. This was successful in rapidly breaking up these tough spots. It is unclear if this simply provided an entrance/exit, or if the direct application of degreasing agent made it successful. It seems reasonable to assume that it was probably a combination. This can be tested by using a needle to puncture a skull with no injection. Unfortunately, larger gauges of needle will be required in order to get through thicker bone on larger mammals which will leave a noticeable hole if either the tooth sockets or foramen aren’t used. This may be cosmetically repairable with minimal effort.

Mobilized grease moves through bone via diffusion. Saponification, dissolution, heat, water movement and grease rendering all impact the speed at which diffusion works. In this case, the degreasing mixture, carried by water, moves towards the hypertonic grease through the bone until it reaches equilibrium. Once there, it breaks down the grease through its typical means and the products are exported through diffusion gradients, moving from areas of greater to areas of lesser concentration outside the bone. Grease itself may move through the bone too, especially when heated in soapy water, to areas of lesser concentration. To expedite degreasing, using fresh water with degreaser in it is important to keep diffusion gradients high. For these reasons, and because it is less likely to harm collagen, it may be reasonable to use lower percentages of degreasing material to save money and increased water change frequencies. 

Water is the most ubiquitous ingredient in degreasing. It is a polar covalent solvent. Almost all applications of degreasing will include water. It serves as a host or diluter for most degreasing agents, soaps, oxidizers and as a carrier of lifted or saponified grease. Typically grease is discarded with water changes as the grease carrying capacity of water reaches its limit, the degreasing agent runs out or both. This can vary in timeframe depending on the amount of grease, heat of solution and strength of degreaser.

Many skull enthusiasts do not realize that long term water exposure can harm bone. This happens through several mechanisms which includes, among other things, bacterial action rotting the collagen, chelation of minerals from the skull, and carbon dioxide interacting with the water to form localized carbonic acid which then dissolves the bone. It is therefore useful to find ways to limit the time a skull is submerged.

Hydrated bone plays a role in the collagen-cross links, which contribute to keeping the collagen tensed. Tense collagen lessens brittleness in bone. Nyman et al (2006) speculate that “loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness” and outline that dehydration in almost all cases results in weaker bone. It is therefore important to be aware that drying bone improperly or using solvents that may dehydrate bone can be harmful. These improper methods may include drying bone in a fume hood or in excessively dry conditions or using solvents such as ethanol or even acetone. Acetone remains a popular and effective choice for degreasing.

Most skull enthusiasts understand that heat mobilizes or renders grease and therefore heat greatly impacts the answer to the a common question: How long to degrease a skull? Favorable temperatures vary based on animals, but typically are around 30 degrees Celsius or less for fish and bird and 44 Celsius or less for mammals. These temperatures for mammals allow for a few degrees of overages from heat controllers, ensuring heat does not exceed 46 degrees Celsius. This is because fats for many mammals melt around 40 degrees Celsius with various culinary references on the internet suggesting bovid fat renders at 55-60 degrees Celsius. Soap, a product of saponification, melts at around 55 degrees Celsius. Collagen denatures as low as body temperature (Leikina et al, 2002). This heat bracket may be most useful in specimens such as arctic fish. The most useful bracket for mammals is 46 degrees Celsius (Lambri et al, 2018) and shrinking in human pelvic elements occurs at 61 degrees Celsius (Danielsen et al, 1994), so a target safely below 46 degrees Celsius is ideal to allow for slight overages from the heaters. A temperature of 48 degrees Celsius is generally accepted as a safe temperature by bone cleaners and taxidermists, though this author has found 46 degrees Celsius to be favorable for not disarticulating the zygomatic joint. Lamellar collagen in bone is more resilient than collagen found in other tissue but there is no reason to use excessive heat when degreasing.

It is the understanding of this author that heat makes collagen triple helixes “bow out” in the middle. This leaves the fibrils more vulnerable to hydroxyl, methyl or other chemical insertion and enzymatic activity. This separation at the cross-links is apparently temporary, and, unless denaturation occurs, the triple helix structure will reform when cooled. This understanding is likely to be refined. It is shared to pass along the idea that heat may be harmful in ways other than denaturation. Collagen experiences time dependent failures when exposed to heat, which may be as low as the animals body temperature (Al-Shaer and Forde, 2025). It is probable that appropriate degreasing heat for animals may be individually derived based on their body temperature.

Heat also increases the speed at which chemical reactions occur. While there are critical temperatures for some reactions that aren’t reasonably achievable because of the collagen heat limit, appropriate application of heat is critical in speeding up the chemical reaction and limiting exposure to water and other potentially harmful chemicals.

Efforts have been made to accumulate fat rendering temperatures by several amateur authors. These temperatures are unreferenced and may not be accurate. As organ fat, back fat and other body-fat rendering temperatures may differ, these may not be laterally comparable to marrow-fat temperatures. This effort may also be futile because finding an uppermost temperature that doesn’t harm collagen is likely the best answer. This is because collagen presents a hard limit for heat, and using the highest possible heat maximally mobilizes the grease.

After testing on both dermestid and simmered skulls, cleaning with very low simmering (sub 60C) appears to provide superior degreasing times because significant degreasing occurs during simmering. It also is far more likely to cause damage to collagen because the margin for error is much tighter. Further excessive heat, such as 100C or greater, will cause loss of protein and “smoothing and softening of the bone” (Bosch et al, 2011). As the collagen is destroyed by heat, it may release CO2, HCO3 or Hydrogen ions. These interact with the hydroxyapatite via ion exchange, causing damage as seen in Bosch et al, 2011 and noted in White and Hannus, 1983.

Saponification is the process by which fats are turned into glycerol and fatty acids. These fatty acids react with hydroxides to form fatty acid salts, also known as soap. This is achieved by combining a base, such as ammonia, with triglycerides like animal fat. There are different strengths and kinds of saponifiers out there, each with advantages and disadvantages. These may be the most cost effective way of dealing with triglycerides but are also problematic for collagen.

Weak bases such as ammonia and soda ash are popular skull degreasers. These bases don’t completely disassociate in water and therefore may throttle the amount of hydroxide in the water at any given time. Unfortunately, other than soda ash, metasilicate and baking soda, other common weak bases smell horrible including ammonia. No matter what type of base is used, hydroxides will be released and saponify. It is possible that controlling the concentration of stronger bases such as lye can produce favorable results like ammonia, though mitigating other processes like oxidation and chelation is a consideration when ions are involved.

One has to consider cost, strength, availability and negative side effects. Because it is covalent and does not oxidize beyond the hydroxides, ammonia is heavily favored in the skull cleaning community despite being a weak saponifier.

Hydroxides (OH) form from every chemical with a pH higher than 7. This includes ammonia (NH3), lye (NaOH), and potash (KOH). The relative concentration of OH is how pH is measured “basic”. Hydroxides react with, or hydrolyze, grease (fats) breaking the ester bonds in the grease, turning them into soap and glycerol. This is called saponification. Glycerols are technically a solvent, but because they are polar and fats are non-polar, fats don’t readily dissolve in them. Hydroxides are known to damage collagen, so should be controlled. It is possible that throttling the concentration of stronger bases, simulating the trickling effect of hydroxides from weaker bases such as ammonia, may make them more viable as degreasers of bone.

Ammonia (NH3) Overwhelmingly the most popular saponifying degreaser of bone. Weak base. It is cheap and readily available. Despite these advantages, it is a poor degreaser. Costs escalate over time and longer times in solution may cause water to damage bone. It is very noxious. Ammonia is a gas dissolved in water. It will off-gas as a result.

Ammonia works by the following equilibrium reaction (Turner-Walker, 2012):

NH3 + H2O  ↔  NH4+ + OH-

The pH of ammonia is approximately 12.5, and about 1% is hydrolyzed at any given time. The hydroxide ion and ammonium bind to some of the fatty acids to form ammonium salts and water. As this happens, more ammonia is hydrolyzed into ammonium and hydroxide, continuing the process until ammonia is used up or off-gassed completely. Importantly, hydroxide ions are known to cause damage to protein (collagen). As a result, ammonia does have bone damaging potential. This is usually negligible, unless the ammonia is overheated, the bone is overexposed, or the concentration is too high.

A common misconception persists in the skull cleaning community that ammonia and soap “cancel out”. Ammonia and soap function in two different and complimentary ways, meaning it is likely that it is more effective to combine them. Many commercially available soaps contain ammonia and cloudy ammonia contains soap. Ammonia breaks down soap scum, which is a deposit of calcium and soap.

Borax Creates a high pH environment and therefore likely saponifies somewhat. It breaks down into boric acid and sodium hydroxide and therefore isn’t ideal.

Potash and Lye Extremely strong degreasers. Easy to source, extreme handling concerns, storage and disposal concerns and noxious. Strong oxidizing agent that will destroy protein including collagen. Not recommended for cleaning bone. Common additives in industrial commercial degreasers in amounts of 0.5-1%.

Soda Ash is a popular hydroxide forming weak base.

Sodium Metasilicate (Also known as waterglass) This is the saponifier used in Bare Bones Solutions degreaser. It buffers at a pH of around 12.5.

When mixed with water hydrolysis occurs and produces orthosilicic acid and hydroxide (Jantschke et al 2014 and Zhang et al, 2015). A silicic acid simply contains a silica attached to an oxide and a hydroxyl group. Silica may play a role in biomineralization and metasilicates are being explored for novel positive interactions because living bone has receptors for the material (Vere et al, 2013). It has anti-corrosion properties of metals and non-metals, due to interactions with the silica. It is used as a bleach stabilizer, slowing rapid decomposition of peroxide and other bleaching agents. Metasilicate is used as a whitening agent in recycled fibers (van Heiningen et al, 1999) providing explanation for the white color of skulls after exposure to metasilicate mixes.

Trisodium Phosphate (TSP) Cheap, powerful degreaser that comes in a powder for cheaper shipping. Do not mix with ammonia because it forms ammonia gas on contact. This was the first substance tested by what would become Bare Bones Solutions. It produces an alkaline solution of pH greater than 11. It is available commercially in both chlorinated and unchlorinated forms. It is versatile, finding use as an anti-bacterial food additive, in stain removal, grease removal, anodizing and more. It is cheap, easy to source and handle, efficient, lacks noxious smell and shelf stable. This gives TSP great advantages as a bone degreaser, though it is too powerful and damages bone even at miniscule concentrations.

It is banned in a dozen states for causing eutrophication in waterways, damages bone over time, and has a low thermal decomposition temperature (73.5C) which means degreasing must be done at a lower temperature. When heated, it can release toxic fumes. It is therefore ill-suited for bone degreasing.

The phosphate in TSP reacts negatively with proteins, including collagen. This is because it is an oxidizing agent. TSP will also react negatively with calcium in bone over time in a process called chelation. In this process, phosphate will bond with surface calcium from the bone to form aqueous apatite in solution.

Surfactants serve several roles, including as wetting agents, emulsifiers and solubizers. Wetting agents reduce the surface tension of water, allowing it to spread more easily and lift grease. Emulsifiers bind liquids that normally do not mix, creating an emulsification. This is achieved by dispersing one liquid as tiny droplets into the other. Non-polar solvents can be emulsified in water, which is highly polar, helping to bend the generalized rule that “like dissolves like”, or non-polar dissolves non-polar (as in triglycerides with non-polar solvents). Emulsifying a non-polar substance in water may have limited success, but some is better than none. Solubizers are used to make grease and other water-insolubles dissolve in water. This process is important, because it aids in mixing of water and grease which normally do not mix. It is accomplished by coating small parts of grease in hydrophilic micelles which then disperse and mix. In many cases, a surfactant will have several roles.

There are two primary types of surfactants available. These are ionic and non-ionic. Ionic surfactants are typically weaker but gentler on skin and eyes. Negatively charged, or anionic, surfactants may denature collagen in small amounts (Nandi et al, 1985). Positively charged, or cationic, surfactants do not appear to damage collagen. Non-ionic surfactants are stronger but harsher on skin and do not appear to damage collagen. They are found in many laundry detergents. Unfortunately, chlorine producing agents are also in many laundry detergents, so care must be taken when selecting a laundry detergent for use. Surfactants add an important element to the grease removal process, especially when used together with saponifiers.

Sodium Lauryl Sulfate and Laureth Sulfate Extremely successful and popular in bone degreasing dish soaps. Used in shampoos and dish soaps because they foam well. Anionic (negatively) charged surfactants that may denature collagen, even in small amounts (Nandi et al, 1985) but that may not apply to collagen bound in bone, as indicated by the widespread success of their use on bone. Sulfates are very weak oxidizing agents.

Several oxidizers have been popular in bone cleaning. They work by accepting electrons from another substance, causing the substance donating the electron to become oxidized. These include chlorine (bleach), peroxide and hydroxide (ammonia). Phosphates and sulphates can also be used. Along with the damage to proteins, some also accept calcium ions from the apatite of the bone in a process called chelation. Oxidizers damage proteins, including collagen in the bone. Chlorine demineralizes bone (Kerbl et al, 2012) in a process that can continue for years.

Hydrogen Peroxide is the most common oxidizer and likely the only devoted oxidizer encountered in skull cleaning. Used ubiquitously to whiten bone in the last stage of cleaning and often to quickly (and poorly) degrease skulls in European mounts. Known to damage bone by forming oxygen radicals in the water-peroxide reaction which then oxidize collagen. It comes in many forms including liquid developer, various percentages of hydrogen peroxide as well as oxyclean. It is often debated which product is superior, but ultimately what matters is percentage, heat applied and time of exposure. As with any chemical, too much heat or exposure has increasingly deleterious effects on the bone.

Organic solvents appear to have the most success (Guilmnot et al, 2014), though they are volatile with low vapour pressures, expensive and are rapidly absorbed through skin (Boman and Maibach, 2000). Polar solvents will be miscible in water and may be less likely to dissolve triglycerides, but not always. Non-polar solvents will not be miscible in water and tend to dissolve triglycerides readily. Choosing the right solvent for the job can be difficult based on cost, disposal, volatility and even danger level.

According to Turner-Walker (2012), the most effective solvent cleaning was a combination of acetone, ethanol and water in a ratio of 1:1:1 with a few drops of a strong surfactant. They added some ammonia as well, which was said to greatly improve the test. Though effective, this may not be the most practical approach due to the volatility and cost of materials used. The following is a list of solvents that is not exhaustive. Many were excluded for lack of availability, extreme toxicity or other unreasonablities.

Acetone Fantastic degreaser. Moderately polar solvent. Grease can be skimmed off the top to reuse acetone. Wicking capabilities make acetone an excellent tool in bone degreasing. Drawbacks include volatility, explosiveness, availability, disposal concerns and higher cost.

Benzyl Alcohol Low toxicity, very polar in water but quite expensive.

Chloroform Great degreaser. Not typically sold at stores. Nonpolar solvent. Likely a restricted substance.

Cyclohexane Fantastic degreaser. Non-polar. Expensive, Explosive, flammable and volatile. Do not heat. Products with this are likely available.

d-Limonene Common natural terpene derived from citrus. Non-polar solvent. Not water miscible. Used in our spot degreaser.

Ethanol Excellent degreaser of bone, highly polar solvent, but may cause staining and evaporates quickly.

Ethyl Lactate Solvent used in Bare Bones Solutions degreaser. Found in wine (Sharma et al, 2025), this green solvent (Dolzhenko, 2020) can biodegrade in carbon dioxide and water (Kua et al, 2014). This solvent is miscible in water and is amphiphilic, meaning it is both lipo- and hydrophilic. It is effective at dissolving both polar and non-polar substances, and works effectively on triglycerides.

Gasoline Strong degreaser that is readily available. Has some non-polar solvents. Drawbacks include volatility, high cost, flammability and explosiveness, lingering smell on the skull and disposal concerns.

Glycol Ethers Group of strong solvent degreasers which was tested by Bare Bones Solutions. Can be polar or non-polar. Some disposal and handling concerns because many are toxic. When considering use, propylene glycol is favorable for toxicity and ecological reasons. Propylene glycol is common in laundry detergents and is highly polar, making it easily miscible in water. Effective at miniscule concentrations of less than 0.5-1% and compatible with many surfactants and emulsifiers. They are known to be effective at cleaning bone (Stemmer and Kehagias, 2018). Glycol may induce warping and other damage in bone. In an experimental mix which included glycol, ostrich skull elements warped and a pig skull became powdery.

Heptane Non-polar. Much success has been found using Heptane, having removed 30% of fats in just 21 days (Guilminot et al, 2014). Expensive, volatile, not miscible in water and toxic. Not recommended outside of proper laboratories. 

Hexane Non-polar. Very hard to source, very expensive with disposal issues. Recommended only for the highest priority and rarest specimens. Not recommended for casual use outside of a museum or laboratory.

T-butyl Alcohol Non-polar. Probably a decent degreaser of bone. Miscible in water but expensive and flammable.

Toluene Non-polar. Decent degreaser of bone. Available in lacquer thinner. Very flammable, expensive and has health risks. Not recommended.

Turpentine Low polarity. Moderate degreaser. Easy to source, price escalates fast, noxious. Not the best choice, but could be useful for smaller skulls if nothing else is available.

Enzymes are catalysts, often proteins, that speed up chemical reactions in organisms. They are successful in some bone preparation (Boyde and Firth, 2004, Bromage et al, 2011 and Irlicht et al, 2002). However, “using enzymatic detergent could be considered risky to collagen in bone” (pers. comm., Wallace, J.*). Detergents contain lipases, amylases and proteases which last approximately 18 hours in solution (pers. comm., detergent company^). A commonly used protease is subtilisin (Maurer, 2004). “Nearly ten” from this family of enzymes are known to damage type 1 collagen (Ran et al 2013). Piazza and Garcia (2014) and Fujimoto (1968) point out that the triple helix of collagen prevents or slow proteolysis. The rate of proteolysis was greater in subtilisins than trypsin (Piazza and Garcia, 2014). Their tests were just 48 hours and despite some of the collagen being derived from bone it was ground in meal and not in situ, creating a discrepancy between their results and degreasing whole bone which requires much longer exposure. Most other enzymes have great difficulty interacting with collagen.

Pronase, a non-specific protease used in some detergents, may also damage collagen rich in hydroxyproline, such as type 1 (Fujimoto, 1968) at thermal thresholds around 35 degrees Celsius. Therefore, if using an enzymatic detergent, a lower temperature may be ideal.

Trypsin is an enzyme used in diaphanization. Thomas and Seymour-Jones (1923) demonstrated that it causes “measurable hydrolysis of the collagen” and Liu et al (2018) claim that “collagen fibres were partially degraded into collagen fibrils by trypsin”. Burns and Meadow (2013) report success preparing bone with trypsin when paired with enzyme detergents.

Bromelin, Papain and other fruit derived enzymes, have also been used. These are added often during maceration. Papain degrades collagen (Wihastyoko et al, 2021) though it may have difficulty with hydroxyapatite-coated collagen.

*Joseph Wallace. Bone Biology and Mechanics Lab, Weldon School of Biomedical Engineering, Purdue University. Email to author, February 15, 2025.
^Detergent company. Phone call with author, April 2024.

Maceration is a useful technique in removing grease from greasy bone. Typically this is done in 30-35 degrees Celsius water, with water changes occurring every 48 or so hours. Cold water applications are successful as well and reportedly much less odorous, but take significantly longer. This should be done ahead of chemical application.

Drilling small holes in tooth sockets, in particular in the jaws and near the zygomatic, can aid in letting grease out and degreaser in to the denser dentary bone. This is potentially favorable because any damage by the drill is covered by replacing the tooth in the socket.

Light has had some success in degreasing (Horak et al, 2022). Their study found that macerated bone achieved a desired condition of degreasing in 21 days in sunlight. Several other forms of light were used, and all appear to have had some success. It is the suspicion of this author that these bones were not only not fully degreased to standard, but that the UV light from the sun damaged collagen.

EDTA or Ethylenediamine Tetraacetic Acid is used in some cleaners to remove blood or metal stains. As a chelator, this is also used to decalcify bone (Alers et al, 1999). It is suggested that this chemical and other strong chelators be avoided except in specific instances.

Vitamin C or Calcium Ascorbate is a chelating agent and is used as a dechlorinator in pools. It may help neutralize chlorine in bones treated with bleach and prevent further damage. Calcium ascorbate is the salt form buffered with calcium, which should make it less damaging compared to ascorbic acid (Vitamin C). Organic acids are used to remove blood stains, so ascorbic acid may have other uses in skull cleaning. Neither application has been tested, but both are hypothetically reasonable. May damage the hydroxyapatite with enough dosage, therefore testing and caution is suggested.

Formation This waxy substance has been studied for over two centuries, and presents novel taphonomy and serious obstacles when skeletonizing dead animals. This material is stable and resilient, often more than collagen and fat, and therefore requires special consideration. It consists of saponified saturated fatty acids (O’Brien and Kuehner, 2007 and Ubelaker and Zarenko, 2011) which may require high pH environments under specific conditions to form (Vass, 2001). In particular, these are myristic acid, palmitic acid, and stearic acid. The ideal pH for formation may be lower than high end degreasers, but still mildly alkaline (Ubelaker, 2023), and require anaerobic conditions at 21-45 degrees Celsius for optimal enzymatic release and bacterial growth (Forbes et al, 2011). Schoenen and Schoenen (2013) report that a lack of both oxygen and “bacterial degradation” is key to adipocere formation. Excellent summaries can be found on google scholar in Forbes et al, 2004, Takatori, 2001, Ubelaker and Zerenko, 2011 and others.

Magni et al (2021) makes a distinction between saponification and adipocere formation, and describes the chemical process in detail. They also indicate Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, some Pseudomonas species and Clostridium perfringens may be involved. B. subtilis generates subtilisin enzymes for cleaners, and C. perfringens can survive in higher pH environments and has a varied diet but prefers glucose. It may be possible to limit adipocere growth by controlling bacterial food sources or growth.

Glucose may be important in adipocere formation because of its role as bacterial food and presence in bone marrow. There may be a different glucose level in marrow than ambient blood levels (Suchacki et al, 2020) due to varying “insulin responsiveness” in different kinds of marrow tissues. Varying diets, such as those in canids and ursids compared to others in the carnivora, should cause the composition of bone marrow tissues to differ (Dzubanova et al, 2024). This may explain the observed tendency of canids and ursids to develop adipocere compared to other canids.

Removal There have been successful reports of some products removing adipocere (Obermeyer et al, 2011). It seems likely that any sufficiently powerful degreasing agent may remove adipocere well. Adipocere naturally forms in high pH environments through saponification. Ammonia is indicated as a remover of soap scum, and may function as a final wash to clean up adipocere residue formed during the process.

The melting point of adipocere is reported as 71 degrees Celsius by Ruttan and Marshall (1917). Melting it without damaging collagen may not be possible because the uppermost heat breakpoint of collagen may only be as high, at maximum, as approximately 61 degrees Celsius (Danielsen et al, 1994, reported shrinking in human pelvises at that temperature). It is well known in art communities that oil melts wax. With a very small amount of olive oil (triglyceride) and a stiff bristle brush, the majority of adipocere was successfully removed from a canid skull in a test. This miniscule amount of oil (less than half of one teaspoon) mostly washed away with soapy water, and likely would degrease away easily.

There is a belief that heating grease will cause it to move “deeper into the bone” and make it harder to degrease. That grease can be moved through dense cortical bone indicates this hypothesis may be incorrect because “deeper grease” should still be movable through bone. This ability may be interfered with by capillary action. An alternative hypothesis is that the triglycerides are crystalizing post-heating. According to Gunjan et al., 2024, slow-cooled triglycerides required ten times the amount of time to degrease successfully with a surfactant. Bone is a decent insulator, and any grease inside it may cool slower as a result. When they cool slower, the crystals are bigger and the lattice is more organized, making it harder to degrease.

Tristearin, a long-chain (saturated) triglyceride, has three or four plateaus as heat changes where crystallization can occur (Hoerr and Harwood, 1956). The lowermost melting point of this triglyceride is 55 degrees Celsius, which exceeds collagen’s comfort temperature. When excessive heat is applied, these crystallization plateaus may be reached. In highly polar solvents, solubility of tristearin limited. In non-polar solvents, solubility is considerably higher. These observations are consistent with grease behavior reported by skull preparators when dealing with skulls with an excessive thermal history. This author hypothesizes that non-polar solvents will likely be more successful than surfactants in handling most crystallized grease.

Triglycerides oxidizes heat. This can also happen during rot in a process called rancidification. There are several relevant products from this process. One is fatty acids, some of which may contribute to grave wax production. Free radicals which interact negatively with collagen may occur (Geng et al, 2023). Oxidized fats can turn dark, and drop in pH as they form carboxylic acid. Other products include aldehydes and carbonyls.

In bone it may be possible for grease to wick and then oxidize, creating a complicated degreasing scenario. Some soaps may find it difficult to dislodge oxidized greases. Oxidizers such as peroxide may also have issues moving these materials because they are already oxidized.  Oxidized greases are typically more difficult to move because their polarity has increased, altering their attraction to some surfaces. They may still react to saponifiers. The typical method of removing epoxies or oxidized greases is solvents.

Rarely, a polymerization of the fats can occur, creating a type of monomeric oxidized epoxy (Khor et al, 2019). These epoxies are likely uncommon in bone cleaning. Epoxies are generally considered one of the better glues for highly porous substrates. Triglyceride epoxies are known to form at or above 160 degrees Celsius (Khor et al, 2019) and provide another scenario for difficult to remove grease post-heat exposure. In a boiling or simmering pot, where bones are at the bottom closest to the heating element, it may be the case that bones are exposed to heat in excess of what is measured. Some epoxification may occur prior to 160 degrees Celsius.

Recommended action is soaking in a non-polar solvent and heat not in excess of recommended guidelines for the animal in question. Unheated acetone may be a great option because of superior wicking and an altered charge on the oxidized triglyceride.

At temperatures above 53 degrees Celsius, collagen fibers shrink by 75% (Maximo and Cunha, 2010). These smaller collagen fibers are more elastic and begins to form disordered gelatins. These gelatins can absorb water and may emulsify fats (Asghar and Henrickson, 1982). Gelatins derived from collagen are often sticky, and in a complex system like bone with wicking capacity they, and any emulsified fats, may be difficult to dislodge.

Ideal temperatures for formation of gelatin are between 80 and 90 degrees Celsius, which are in ideal simmering range for bone preparation. This may provide an explanation for “fats moving deeper into bone” or “fats cooking into bone” when overheating bone. Small amounts of collagen may suffer negative alteration as low as 45 degrees Celsius (Maximo and Cunha, 2010) which suggests ideal degreasing temperatures for adult mammals could be 44 degrees Celsius.

Capillary action uses intermolecular forces or cohesion from surface tension and adhesion between the liquid and surface of the bone to draw liquid into the narrow spaces of the bone. Heat causes the cohesive force to weaken and the adhesive for to strengthen. The net result is an increase in capillary activity, or in the case of water and grease, an increased wicking movement into the bones confined spaces. A heat threshold may exist which causes a critical movement of grease in bone, leading to increased difficulty of degreasing. It is possible that chemically mobilized grease may more successfully wick into bone.

Bone degreasing has many options and there is no silver bullet or universal technique. Online resources are disparate, discombobulated, amateur and largely unreferenced. It is the hope that this information may remedy some of these issues and begin to organize some of the information in a more formal and accessible way. Please reach out if there are errors.

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