The preparation of animal skeletal remains for study, articulation, or display requires patience, safety, and a practical understanding of biological decomposition. The goal is to isolate and preserve the osseous structure by safely removing all soft tissues, residual fats, and oils. The methods discussed here provide a practical and ethical approach to achieving a professional-quality skeletal element.
Essential Preparations and Legal Considerations
Before beginning any decomposition process, it is important to address safety and legal compliance. When handling animal remains, protective equipment is mandatory to guard against potential pathogens, such as bacteria and viruses, that can persist even after death. This includes wearing durable rubber gloves and, for specimens with significant soft tissue, a P2-rated mask to prevent the inhalation of aerosols and dust.
Determining the legal status of the specimen is equally important, as laws concerning the possession of wildlife vary significantly by location and species. Federal statutes, such as the Migratory Bird Treaty Act of 1918, strictly prohibit the possession of any part of most native bird species, including feathers, nests, and bones. Similarly, possessing the remains of animals protected under the Endangered Species Act is illegal without proper permitting. To avoid legal issues, the animal must be a legally hunted game animal, a domestic animal, or a common, unprotected pest species.
Water Maceration: The Preferred Method
Water maceration is the most effective and least damaging technique for skeletal preparation. This method relies on naturally occurring anaerobic bacteria to consume the soft tissue by submerging the carcass in a sealed container of water. The bacteria thrive in the low-oxygen, nutrient-rich environment and break down muscle, tendons, and ligaments without damaging the bone structure.
For optimal results, the water temperature should be maintained between 80 to 100 degrees Fahrenheit (27 to 38 degrees Celsius) using an external heat source, such as an aquarium heater. This warmth significantly accelerates bacterial activity, reducing the decomposition time for a medium-sized skull from several months to a few weeks. The process must be conducted outdoors or in a highly ventilated structure, as the anaerobic breakdown of tissue produces a strong, offensive odor due to the release of volatile compounds.
Routine maintenance involves periodically checking the water and changing it when it becomes excessively murky. The process is complete when the remaining tissue appears sloughing and can be easily removed from the bone by hand or with a gentle spray of water. The bones are then ready for the next stage of cleaning, ensuring all fragments, including small teeth, are recovered from the container.
Natural Decomposition Methods
Alternative methods offer less control and carry a greater risk of damaging the final specimen. Burying the remains in soil is a common approach, where soil microbes and invertebrates, like beetle larvae, facilitate the breakdown of tissue. The time required is highly variable, often ranging from six months to a year or more, depending on soil temperature, moisture content, and the size of the animal.
Drawbacks to burial include potential staining of the bone from soil minerals and organic matter, which can be difficult to remove later. There is also a significant risk of bone loss, as small skeletal elements may be scattered or destroyed by burrowing animals before they can be retrieved. Surface exposure, or simply leaving the carcass outdoors, is the least recommended method due to the high probability of scavenging animals carrying off or destroying the bones. This method also leaves the specimen fully exposed to weather fluctuations and insect damage, which can leave permanent marks or erosion on the bone surface.
Degreasing and Whitening
After all soft tissue has been removed, the bones must be degreased to remove residual oils and fats that cause a greasy appearance, yellow tint, or odor. Degreasing is accomplished by soaking the bones in a warm water solution containing a non-sudsing household degreaser, such as clear dish soap. Heat is beneficial as it thins the grease, allowing it to leach out of the porous bone structure more quickly; this process can take several weeks to months for very greasy specimens.
Once degreased, the bones can be whitened using a dilute hydrogen peroxide (H₂O₂) solution, which acts as a gentle bleaching agent. While 3% hydrogen peroxide will work, a higher concentration of 12% is often preferred for faster and brighter results. Soak the bones until the desired whiteness is achieved, typically 24 hours, and strictly avoid using chlorine bleach, as it causes the bone’s structural matrix to become brittle and flaky.