Rendering a carcass into a clean skeleton is a meticulous process that combines science, technique, and patience.
This guide outlines the essential steps—defleshing, degreasing, and whitening—along with various methods and best practices to ensure successful results.
Steps to Render a Carcass into a Skeleton #
There are generally three main steps involved in rendering a carcass into a skeleton:
1. Defleshing
2. Degreasing
3. Whitening
These steps are most effective when done in sequence.
• Chlorine bleach should never be used in any part of the process, as it damages bone structure.
• Avoid cooking bare bones, as it can fix grease in the bones and cause long-term damage.
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1. Defleshing #
Defleshing is the first and most important step. The more flesh and skin removed initially, the faster and less odorous the process will be. After defleshing, remaining tissue should be removed carefully with tools such as tweezers, scalpels, or brushes before proceeding to degreasing.
Methods for Defleshing #
Open Air: This is one of the fastest methods. You allow the carcass to decompose naturally, relying on flies and insects to remove the flesh. A locking cage is essential to protect the carcass from scavengers. Skinning or gutting the animal isn’t necessary, as the skin can help retain moisture, though extra holes may be poked for maggots to enter.
However, this method has significant drawbacks, including a strong smell, the need to keep the carcass moist, and a potential fly infestation. It is most effective in warm, humid climates and should only be attempted far from residential areas.
Dermestid Beetles: A great option for those able to sustain a beetle colony, especially in winter with a heated setup. Dermestid beetles are ideal for preserving the integrity of fish, bird, and small mammal skeletons, which might otherwise disarticulate with other methods.
However, the colony requires proper ventilation and feeding, and escape can be disastrous.
For more details, refer to the Natsca Dermestid Guide.
Burying: This method works well for larger carcasses or small animals in pots. It produces minimal odour and simplifies cleanup. Bury the carcass at least 60 centimetres deep to deter scavengers, and place rocks or a mesh over the site to protect it.
Keep the soil slightly moist to aid decomposition. Decomposition times vary depending on local soil conditions, but larger carcasses typically take several months.
Adding compost or bacteria can help speed up the process. Mark the burial site to locate it easily later.
2. Degreasing #
Once defleshing is complete, degreasing is the next step. This is often the longest part of the process, as bones need to be thoroughly degreased to prevent long-term yellowing or oily spots.
To begin, submerge the bones in a container filled with water and a degreasing agent. Liquid dish soap works well, particularly clear, colourless varieties that won’t dye the bones. Laundry detergents are less effective and may stain the bones, though enzymatic detergents like BIZ work well and can speed up degreasing.
• Change the water and soap mixture regularly, typically at least once a week, or whenever the water becomes cloudy.
• Continue degreasing until the water no longer clouds after a week. Any yellowing or oily spots on the bone indicate that further degreasing is required.
Alternative degreasing agents like acetone or ammonia can also be used. However, these have specific safety concerns:
• Ammonia is an irritant, so ensure proper ventilation and wear a respirator. Avoid emptying ammonia solutions near vegetation, as it can be harmful to plants.
• Acetone is highly flammable and toxic. It cannot be diluted with water and should be handled with care, using a tightly sealed container to prevent evaporation. Acetone also dissolves plastics, including some buckets and gloves, and cannot be disposed of down household drains.
When used correctly, acetone works faster than other methods and can be reused for multiple batches of bones.
3. Whitening #
After degreasing, whitening is an optional but popular step to improve the appearance of bones. Whitening is primarily cosmetic but also helps sterilise the bones.
Hydrogen peroxide is the safest and most effective whitening agent. Standard 3% hydrogen peroxide (available in stores) works well, though higher concentrations such as 12% can be used with caution. Pool supply stores may also carry stronger solutions, but ensure they do not contain added chemicals.
To whiten, simply submerge the bones in hydrogen peroxide until the desired whiteness is achieved. When using 3% hydrogen peroxide, no dilution is needed. For stronger concentrations, consider diluting to reduce the risk of over-whitening or damaging the bones.
• Keep the container covered and out of direct sunlight to prevent hydrogen peroxide from degrading.
• Avoid using chlorine bleach for whitening, as it damages the bone’s collagen, making it brittle and powdery over time. This degradation is irreversible.
An alternative to hydrogen peroxide is sun bleaching. However, this method takes significantly longer, exposes bones to the elements, and offers less control over the whitening process.
4. Drying #
Drying is a critical final step in the process. Bones are porous and contain organic materials, so drying them too quickly or unevenly can lead to cracking, warping, or delamination.
• Allow bones to air dry slowly, away from direct sunlight or high heat. Avoid baking or using artificial heat sources, as these can cause damage.
• Bones may feel soft immediately after whitening, particularly for fish or bird skeletons. Let them dry fully to re-harden before handling.
Teeth may occasionally crack during the drying process. This is common and can be fixed by gluing the pieces together once the drying is complete.
Additional Methods & Notes #
Maceration #
Maceration is one of the most effective defleshing methods, though it is also the smelliest. This method involves soaking the carcass in warm water, allowing bacteria to break down the flesh over time. You will need a large container, water, and a way to maintain the water temperature above 21°C (70°F).
• Stirring the water daily will help speed up the process, but it can be unpleasant due to the odour and floating tissue debris.
• Replace the water regularly, especially in the early stages when it becomes heavily fouled. Retain some of the bacterial scum during water changes to preserve the bacterial population and keep the process efficient.
If the water temperature drops too low, decomposition will stop, and fats may convert to adipocere (bone wax), which is very difficult to remove. Under optimal conditions, maceration can reduce a fleshed carcass to clean bones in a few weeks.
Avoid adding antibacterial dish soap or hydrogen peroxide during this step, as these will kill the bacteria necessary for soft tissue breakdown. Instead, you can add enzymatic detergent to aid the process. Enzymatic detergents like BIZ dissolve tissue and fat simultaneously, effectively combining the defleshing and degreasing steps.
• Bones may appear discoloured during maceration if water isn’t changed frequently, but this can be addressed during the whitening stage.
Simmering #
Simmering or cooking should only be used for larger animals and as a last resort. This method involves placing the carcass in water heated to a low simmer. Never boil the bones, as high heat can warp them and make degreasing much harder.
• To protect the bones, it’s best to simmer the carcass with flesh intact. Overcooking or leaving the bones in hot water for too long can cause irreversible damage.
• Once the flesh loosens, it can be removed using a pressure washer or hose, but this requires caution. Pressure washers can easily destroy fragile bones or skulls.
Simmering is not suitable for birds, fish, or small mammals, as their bones are too delicate to withstand the heat.
Final Considerations #
Each method of defleshing, degreasing, and whitening comes with its own set of pros and cons. Your choice will depend on factors such as the size and type of the carcass, available space, climate, and personal tolerance for odours.
Throughout the process, patience is key. Rushing or skipping steps can compromise the integrity of the bones. If followed carefully, these methods will allow you to preserve clean, durable skeletons for display, study, or personal projects.
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