Skeletal Specimens for Scientific Studies
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Published: Fri, 08 Jun 2018
This report is about the proper techniques for preparing, cleaning, whitening and articulation of skeletal specimens for osteological, biological, veterinary or zoological study. It will explain the three usual techniques used to clean the bones of soft tissue and a few of the more uncommon ways to do so. It will go slightly in depth in each category and then move onto the proper ways and improper ways that the bones themselves are whitened and all lipids are removed from the bones, than it will discuss how to seal the bones to protect them from the elements. Then it will discuss actual articulation and go into detail on the types of articulation commonly used. Lastly it will go over common uses for prepared articulated skeletons.
Skeletal articulations have been going on since museums first started displaying taxidermied animals. Many times the animals bones didn’t want to be wasted so either the skulls or entire skeletons would be saved in archives to help accurately catalog specimens kept in the museum. Eventually the idea was had to reconstruct these skeletons into lifelike poses and display them in the museum as well, this is where skeletal articulation found its roots. In the picture below is an example of an articulated skeleton of a Potto, a species of primate
There are multiple ways to clean the specimens that are used for articulations. There are three common ways that it is done with satisfactory results, the first and most common method is with the use of the beetle Dermestes maculatus, otherwise known as the dermestid, or skin, beetle. These beetles start their life as a small microscopic egg typically laid near dried animal material, which than hatch out as small furry larvae which are black to brown in color. The eggs typically take a day to hatch and the larvae go through multiple stages, or instars, before finally pupating and emerging as an adult. Post, L (n.d) Bone Builders notebook. Pg. 21 Homer, AK, Author published. The male beetle attracts the female with pheromones, which is a common method in the insect world. There is no intermale aggression or territorial aggression.
These beetles are useful not only in skeletal articulation but also in the field of human forensics. The main way these beetles assist in the cleaning of bones for articulation is they eat the flesh fairly quickly, the larger the colony the faster the job gets done. With a colony of one thousand beetles an animal the size of a weasel could be cleaned overnight, as opposed to some of the other methods which take considerably longer. An example of a small colony cleaning a deer skull can be seen in the below picture
The beetles are also extremely delicate and thorough in the job that they do, being able to clean even the skeletons of young animals without fully formed bones while doing little to no damage. B. Shaver & P.E Kaufman (2009). They also allow articulators to perform ligamentary articulations. A drawback to using beetles for cleaning is they often leave a lot of fat in the bones, making for a longer whitening and degreasing process. Beetles usually live for around 6 months in their adult form, however they breed very quickly. I have personally raised a colony of these beetles from just eighteen beetles to well over five thousand in a little over a year.
A second common method for cleaning bones for use is maceration, which requires less maintenance than a beetle colony but also takes a lot more time to fully clean the bones. Maceration is the submersion of the specimen in water to decompose fully. This is further broken down into two categories, cold water maceration and warm water maceration. Cold water maceration typically takes a longer period of time to completely decompose the specimen, however it is easier maintenance and is typically used in warmer climates. Warm water maceration usually uses some form of heating element in the water to speed up the process of decomposition. It also has the added benefit of helping to melt some of the lipids left in the bones, helping to degrease the bones while cleaning them at the same time. Maceration when used properly results in much cleaner bones than the other methods of cleaning, however it takes a considerable amount of time to complete. Times can vary from a week or two for a small animal like a mouse to a few years for larger animals such as horses and cattle. Generally the water temperature is kept at or above 80 degrees for warm water maceration. This dramatically lowers the degreasing time by melting and liquefying the lipids in the bones, making it easier for the bacteria to consume and for physical removal of the fat. This techniques major drawback is mostly the smell it produces, which if never smelled before has been known to produce ill responses.
Most of the time maceration is done in small containers with separate bone groups separated from each other, for example the arm bones separated, the leg bones separated, and the ribs and spine separated. This makes it much easier to rearrange the bones after the cleaning process is done. These sections are often placed in mesh bags made of some form of plastic, as if it were a form of cloth it could potentially also be digested and consumed by the bacteria in the water. Other times specimens may be placed in wire cages and placed in streams, rivers, or ponds to macerate, which also allows natural scavengers to help do the work, however there is a far greater potential to lose bones this way, or have it tampered with.
A third common technique for cleaning bones is “boiling”. This technique involves actually cooking the specimen for multiple hours until the soft tissues become soft enough to come away from the bones. There are several problems with this method and the main one being that people tend to actually boil the bones, damaging them with the heat and making them soft and flaky. It is best to simmer the bones on low heat for a long period of time to help avoid from damaging the bones. Often times the heat tends to leech the fat directly into the bones, making for a terribly long degreasing process. This technique is commonly employed by taxidermists for “European mounts”, which is keeping the skull and horns of game animals such as deer or antelope. A European mount may be seen in the below picture
Some people will also add baking powder to help strip the soft tissue from the bones, this is highly damaging to the bones and though initial results may look alright, without proper sealing the bones will soon turn dusty and deteriorate overtime, until you are left with nothing more than dust. This process is also usually done in pieces so as to make organization of the skeleton a simpler process. Times can vary from a few hours for smaller sections of bone to well over twenty four hours for larger animals or sections of bones. Often times the spine of the animal will present a problem as there is much cartilage, nervous tissue and muscle tissue holding them together. Manuel removal of flesh is required for this technique, often involving fine scalpel blades and knives, as well as stiff wire brushes.
Overall this technique is the least efficient of the three common techniques and has the most potential for damaging the specimen, therefore it is often not recommended to be tried by those first starting skeletal articulations, as they are more prone to make careless errors and mistakes. The most efficient and time efficient method of the three common methods is using dermested beetles.
There are many more ways to clean the bones of specimens for display however now I will discuss just two of the more uncommon ways of doing this. The first less uncommon way of cleaning bones is simply burying the specimen in the ground and allowing nature to do the work. Often times the specimen is placed in a cloth bag and buried so as to not lose bones, however the cloth bag can also be effected by decay, and be eaten away in the soil by invertebrates and bacteria naturally present there.
Bones are commonly lost using this method and it may take several years for the soft tissue to effectively be decomposed even in small specimens. A large problem with using this method is the fact that minerals are naturally found in the soil and often will leave orange or rusty red stains on the bones due to the presence of iron in the soil. These stains can be removed but not always thoroughly using strong chemicals which also damage the bone; this is not an optimal situation.
Sometimes after removing the bones from the ground it will be discovered that the soft tissues have “mummified” to the bones, making it very hard to remove. This happens frequently in warmer dryer climates. The dried tissue than has to be removed manually with tools and than most of the time needs to be “boiled” or put into a dermested colony, defeating the purpose of putting the specimen in the ground to begin with.
A second uncommon technique used for cleaning is using chemicals to remove the soft tissues. L. Post (n.d) Bone Builders notebook. Pg 24. Homer, AK, self published. Commonly household drain cleaner is used for this process, as it eats away at the soft tissue by either being strongly acidic or basic. Other times fifteen percent or higher hydrogen peroxide is used as it oxidizes the flesh. A drawback to this technique is the obvious danger of using strong chemicals which may severely burn the user. These chemicals if not used in proper percentages can completely eat away a small specimen in just a few hours, so a close eye has to be kept on the entire process. Often times the ligaments are the last parts to be dissolved and with proper timing can be used to make a ligamentary articulation.
The benefit of these techniques are they are fairly hands off, however there are often multiple things that can go wrong and ruin a specimen or possibly even harm the articulator. Some of these techniques are still new to practice and must be tuned a bit more to get proper results. Often times it is best just to use those techniques which are proven safe and effective as they are the ones that have most likely been around the longest. Those who wish to start skeletal articulations are often suggested to ask the area museum of natural history what their opinion is or which technique they employ for their own skeletal displays, they will often be more than happy to help you.
After proper cleaning of the specimen has been achieved it is necessary to remove all fat from the bones and make them as white as possible for a clean looking display. By removing the fat not only are you making the skeleton look better but also you are removing a possible source of bacterial growth and unsanitary conditions. This also helps to lessen the risk of possibly having the skeleton have any off odors of decay, not what is wanted for proper display of specimens.
Often the first step to degreasing is doing a preliminary soak in hydrogen peroxide, three percent for smaller skeletons or up to thirty percent for larger bones or skeletons, though thirty percent hydrogen peroxide can be an extremely dangerous chemical, and all proper precautions must be taken. Hydrogen peroxide works on the principal of oxidization, which is the removal of one or more electrons from a chemical composition. Basically oxidization is what causes rust to occur on certain metals. By removing an electron, the chemical composition of the substance is changed. In this instance it makes bones turn from a natural color to a brighter white.
This first preliminary soak in hydrogen peroxide whitens the bone in areas where less natural fat deposits are occurring, typically at the ends of the bones away from the marrow in the center of most long bones. By whitening these areas first it reveals the areas with the most fat present, thus making an area to target for the actual degreasing process. Without doing this first preliminary soak it would make the process of degreasing longer and require more water changes than what might truly be necessary.
There are a few different ways to go about degreasing the bones of specimens used for articulation. The two most common methods are using ammonia and using some form of detergent in warm water, both being an effective means of degreasing bones, however the detergent method is a bit more complicated. When using ammonia to remove lipids from bones it is usually done using uncut household ammonia, though this is not the strongest form of ammonia that can be used, it does the job and is the safest to use. It does not need to be warmed to be effective, however the warmer it is the faster it acts on the fat molecules in the bone.
When using the detergent method for degreasing it is common to use one cup of detergent per five to ten gallons of water. Using straight detergent has been done before but often leaves less than desirable effects, such as discoloration of bone. An aquarium heater or other form of water heater can be used to warm the water in the container, making the detergent act upon removing the fat a bit faster. With small skeletons this method may take a few weeks to a month, but with larger bones and skeletons it may take several months and several water changes to reach the desired effects. With the ammonia method it usually takes a shorter period of time than if you were using the detergent method, from a few days for small bones to a month or two for larger skeletons.
It is very important to protect the bones and skeletons that are being worked on from the elements and the natural passage of time. There is more than one way to do this and most are effective. The first and most common way to seal bones is using a dipping technique using a mixture of Elmer’s glue and water. The glue tends to be soluble in water and it is a very natural and non-harsh way to treat bones. The whole skeleton or bone is dipped into the mixture and allowed to dry, the glue naturally forms a clear protective layer over the skeleton however if it needs to be removed all that need be done is for it to be re-dipped in hot water and the glue will melt off.
Reasons why the glue, or any sealant, might need to be removed range from grease coming to the surface of the bone or skeleton after it was thought it was all removed, which can be a frustrating and disheartening occurrence, to the skeletons position needing to be changed, for any number of reasons. Sometimes the sealant might need to be removed because a new, more reliable sealant has been found, with the first being used temporarily to protect the bone from harm.
Sometimes damaged skeletons can be salvaged if using the correct sealant. If the bone was compromised during cleaning, often from harsh chemicals or too much heat being applied, the sealant will keep the bones from coming apart or further cracking. The teeth of large carnivorous mammals have a tendency to crack over time due to moisture in the teeth slowly evaporating, and when a liquid evaporates into a solid it takes up more room, cracking the tooth. This can be avoided by placing the tooth in a drying material such as rice or cotton, and letting it sit for a few weeks to a few months. The tooth is than covered in a clear strong sealant, clear nail polish being a good example of this. Several coats are applied to make the tooth very strong and stable. The same procedure can be applied to the keratin sheath on the claws of animals.
Another method of sealing bones or skeletons involves buying a clear spray paint from a reputable brand that is known to not yellow over time. The skeleton or bone is laid out in a ventilated area and sprayed in several coats of the spray paint and allowed to dry. Depending on the type of paint used the sealant will either appear dull and non-reflective, keeping the natural properties of the bone, or it will appear to be shiny and reflective, which often times may be applied to teeth and claws for those who keep private collections of skeletons for their own research. Typically in a museum quality specimen a flat coat is used to keep the bones looking as natural as possible. Other times no sealant is used at all on bones which have been professionally cleaned, and the bones or skeletons are simply kept under glass or in a display case, to protect them from dust and the oils found on human fingers and skin.
Several types of articulations exist and are used in different manners for different institutions or research. Articulations and collections can be broken down into personal collections, museum or educational collections, or veterinary models, though often times in recent year’s replicas and reproductions are used for this purpose as they are often cheaper and far less fragile. Articulations and collections for personal use can be found in the homes of hunters, taxidermists, medical and veterinary students or just those people who are interested in natural history, anatomy or biology.
Skull collections are often a simple and less complicated means of having an inventory of collections for certain species without having to do full skeletal articulations, these are fairly common in the homes of hunters and taxidermists. Those who keep full skeletal articulations often times have them on bases or in a natural habitat type setup. Often, those who are more interested in the general anatomy of the skeletons themselves have free standing skeletal articulations or those without bases, These are simpler to complete and may sometimes require bars to keep the articulation stable and from falling and possibly becoming damaged.
Free standing articulations of smaller animals may be done through the use of ligament articulations. This involves letting a dermested beetle colony clean the skeleton, and watching the process very carefully so as to know the precise time to take the skeleton out of the colony. This takes practice to do, but when done right can make articulations much easier to complete. Essentially the beetles eat away all soft tissues except those ligaments which are holding the skeleton together. Often one or two bones may break away from the main skeleton but can easily be reattached at the time of the actual articulation. Than the entire skeleton goes through the degreasing process and during this time the ligaments are kept hydrated, making the skeleton very flexible and easy to manipulate.
A stand may be built and pins used to put the skeleton into the position that you want it to dry in, though as ligaments dry they begin to contract and become hard, and on small enough animals such as mice, may not be visible at all. It is often necessary to re-align bones that shift during the drying process, as contraction of the ligaments causes them to move around, but if it dries in a position not right, all that need be done is for the skeleton to be re-hydrated and posed again. Once the skeleton is dried in an acceptable pose the pins and remove the support frame and often times the skeleton may be free standing.
With larger skeletons, more tools and work may be involved. Common tools used for articulation of larger skeletons include drills, pins, eye screws, and metal pars or wiring. Where ligaments would normally hold bone to bone, metal pins sunk into the joints may be necessary, and these are often siliconed into place so as not to come apart again. An example of a cougar skeleton on a base may be found below
A bar is often ran up the neural canal of the spine and reshaped to form the natural arch and support found in the spinal column of most vertebrates. The rod terminates after entering the foramen magnum of the skull, and may then be epoxied into place to keep from coming apart. There is naturally cartilage which attaches from the ventral end of the ribs to the sternum, to be as accurate as possible this cartilage must be rebuilt. The cartilage is often rebuilt be using thin wires which come from the sterna end of the ribs and attach to each other and to the sternum, and are than covered in layers of clear silicone to replicate cartilage.
Another interesting articulation which is rarely seen is known as the Beauchene skull, which was first developed for human skeletal articulations by a French anatomist named Claude Beauchene in the mid eighteen hundreds. Cult of weird staff (n.d) Beauchene skull, retrieved from Cult Of Weird website http://www.cultofweird.com/medical/beauchene-skull/. This type of articulation is where the individual bones of the skull on one side of the skull are removed from each other in an “exploded” manner, so that the internal anatomy and the individual bones may be studied. This is a very infrequently seen articulation in animal skeleton articulations.
Young animals may also be used in skeletal articulations, and though it may be sad to think that a young animal lost its life before it could grow into an adult, they are also an important research for the continuation of Osteological study. The bones of young animals are often much softer and not fully connected which makes for a more difficult articulation. Young animals also usually contain more bones than adults, as the individual bones grow they form together to make larger bones. These skeletons may be used in comparative anatomy with the skeleton of an adult of the same species of the animal. Young animals require a much finer touch and can usually only be cleaned through the use of beetles, as other cleaning techniques that were previously discussed will most likely be too harsh on the young bones, resulting in damage or complete disintegration of the bones.
Skeletal articulations may also be used in area nature centers in parks, to help demonstrate the local wildlife in that particular area. They are found in taxidermist shops to help promote business and show the skill of the taxidermist who owns the company. Often time’s larger universities have a colony of dermested beetles to help demonstrate to students the natural life cycle of the beetle for entomology students while also having an inventory of bones or skeletons for other majors of the college, such as anatomy biology or zoology.
Skeletal articulations are a necessary component of anatomical and other fields of study. Without the use of skeletons for research we would never know how bones connect to each other, how different teeth of animals are used for different food that the animals ingest and how certain animals from certain families have unique evolutionary adaptations, such as the cat family, with their retractable claws, or the pinniped family, who’s limbs have evolved into flippers, but are still able to haul out on land to escape predators from the ocean. Skeletal anatomy is important to most if not all biological sciences, and without skeletal articulators there would be far less to look at in your favorite natural history museum, and we may never have known what dinosaurs skeletons may have looked like properly articulated. The next time you take a look at a skeleton in a museum, think about the hard work and patience that went into putting that skeleton together.
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