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Skull Preparation
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A lot of the queries I receive via this website are about cleaning skulls (hence this page) and safety precautions which ought to be taken when handling skulls or dead animals. As regards the latter, I don't think there is a significant risk - just take basic precautions like washing your hands. If it is infectious diseases you are worried about, avoid live humans, not dead animals ! This advice is by no means the last word on the subject - I am still experimenting. If you have criticisms or experience to share, drop me a line! All bones have "meat" firmly attached to them, and what gives meat, tendons and ligaments their tough, fibrous structure is protein. The skull collector can cleanly remove all the "meat" without damaging the bone by :
Remember, though, that bone also contains protein as part of its structure, and any protein denaturing process taken too far will start to attack the bone, resulting in the surface losing its ivory texture and becoming chalky or even crumbly. Bones also contain fat in the marrow, sometimes quite a lot, and if this is not adequately removed it can migrate to the surface causing staining (As in the jawbone of my cattle skull). Eventually the fat will become rancid and acidic, which can damage bone and other nearby specimens. Some collectors use degreasing agents such as acetone, petrol or ammonia, but these are all dangerous, and the other methods described here should remove most fat from skulls. You can help the fat to leave large bones, such as limb bones or the cattle jawbone mentioned above, by drilling holes to permit circulation of water or other solvents. A basic skull cleaning kit should contain a scalpel, with spare blades, tweezers, scissors, probes (mounted needles), blunt table knife (scraper), pipecleaners, old toothbrushes and if possible, a syringe. Hot and cold running water are necessary for rinsing etc, and if a flexible tube can be attached to the tap so much the better. You will need a supply of paper towels, cloths, containers, etc. Simply remove as much flesh as possible, without risking damage to delicate parts of the skull (underneath). This normally means skinning the head, and removing the eyes, cheek muscles and tongue. The brain is more difficult to remove, but you should try to "scramble" it with a suitable probe so that the broken pieces can be removed by syringing. Sometimes it is easier to remove after treatment has solidified it. The beautifully whitened bones that you find outdoors have been cleaned by insects, and whitened by weathering, and a jolly good job they make of it too, but they have probably taken several summers to reach that stage. Colonies of flies or beetles can be maintained year-round but this requires specialist equipment and knowledge - and they smell ! The best results are obtained from the larvae of Dermestes beetles, which will delicately remove the flesh from a skeleton, leaving the bones articulated. For the casual skull collector, the best "insect" option is to put your head in the freezer (ha ha) and wait for summer. Maggots will soon colonise anything dead, and quickly remove the flesh. They are, however, very energetic and enthusiastic, and will separate small bones and especially teeth by their activity. Put the head in a container (e.g. a margarine tub, with some small holes for drainage) or net bag (the sort of netting used for net curtains or childrens' fishing nets) which will ensure retrieval of all the parts. Remember, too, that larger animals such as cats, dogs, rats and crows (and in America, bears & raccoons) may take an unwelcome interest. Maggots like to work in a damp environment, where their activities reduce the soft parts to a stinking "soup". In summer, small carcasses or heads tend to dry out, often curtailing the maggots' activity, so it may be a good idea to place the head in an open polythene bag to allow access by flies, while retaining moisture, or cover it with leaf mould or compost. When you think the process is nearing completion, remove the skull and boil it briefly, then wash it carefully, watching for loose bones and teeth, otherwise the disgusting effluvium will stain it. "Wild" dermestids can also be found in summer, by the entomolgically adept, in partially dried out carcasses. Such partly decomposed heads found in a dried condition, with some mummified skin attached, can usually be cleaned by soaking in detergent solution until the skin etc softens. Everyone knows that boiling eventually softens meat, and ten to thirty minutes, depending on size, will enable you to remove muscle sheets from the upper surfaces. It is the tough, gristly bits where the neck was attached which can cause problems, requiring such extended boiling that the structure of the bone is affected. Also, boiling does little to remove material inside the nasal and other cavities."Slow cooking" is possibly better than boiling - just as in cooking, it gets meat really tender. Don't pressure-cook bones, they tend to disintegrate ! Bring the skull up to temperature gradually, if you drop a cold head into boiling water you may crack teeth or split the skull due to pressure buildup. Boiling works better if you allow the head to decompose for a week or so beforehand - like hanging meat to tenderise it - but more so. The subtlest and best way to soften and dissolve protein (and remove fat) is with enzymes. Enzymes are biological catalysts (please tell your local health food shop manager), and each is designed to make or break one particular type of chemical bond. Proteases - the type which break down proteins - can easily be obtained from two sources: 1. Bacteria break down ("rot") carcasses by releasing proteases. They will do this for you, especially if you give them ideal conditions. The standard method, called "maceration", involves keeping the head underwater in a warm place, the nearer body temperature you can get, the better. The process takes anything from a few days to a few weeks but can be speeded up by boiling for a short time before starting the maceration and stripping off as much flesh as possible. Also by brief boiling at the end to dislodge remaining traces. The advantages of this method are the very good quality results obtained, and its extreme simplicity, no skill or special equipment is needed - just a margerine tub or similar (with a top !). The disadvantage is the smell. It will take some resolution to remove the top after a few days. Open it out-of-doors, where you can pour the liquid away onto the soil, and if your friends start to avoid you, you will know you must have splashed a drop onto your clothes. The finished skull will smell for several months. 2. Biological Washing Powder The substances which ooze from our vile bodies are mostly fat and protein, so some types of washing powders contain enzymes which dissolve these substances very efficiently. Unfortunately, they also contain other chemicals so look for "green" varieties such as Biotex or Ecover. The enzymes in washing powder remain active up to 50 or 60'C, so for quickest results, a device which maintained a quantity of water at around this temperature would be ideal. A DIY-ist should be able to make one, there must be thousands of varieties of thermostats designed to keep domestic hot water at around 60'C. Otherwise, try a "slow cook" electric casserole, an incubator, an aquarium heater, a home brewer's heated mat or a thermostatically controlled boiler. In the US, meat tenderiser may be worth trying as a source of protease. Most of the above treatments will leave you with a more or less clean skull, somewhat smelly, perhaps stained, with loose teeth and small bones. 1. Collect together the detached teeth and bones, test any remaining teeth and remove loose ones, likewise with loose bones, such as nasals. Once dried these can be glued back in place. 2. Thoroughly rinse the skull under running water. If you can hold it 12 inches (30cm) or so below a tap, where the stream breaks up, the water gives greater agitation. Pay particular attention to all foramens and other cavities, and try to blow out remaining material. This is where a rubber tube is useful, especially with the channel running from end to end of the jawbones. With very large skulls, such as cattle, take them along to the filling station, and use the high pressure car-washer on them - but go at 3am ! (Be careful, don't put the nozzle too close to the skull - these are very high pressure jets.) 3. If you feel the skull could do with some bleaching, take it easy - any kind of crude chemical treatment is likely to damage the surface of the bone. I use very dilute hydrogen peroxide. If the skull is badly stained, you are unlikely to be able to whiten it completely. 4. Dry it thoroughly. Remember there are many cavities inside bone, which will take a while to dry out. These will probably still contain some organic material, which will cause problems if stored damp, especially if sealed in a polythene bag. Always puncture bags to allow air circulation and avoid condensation. If there are still intractable bits of gristle attached, or if you know that material remains inside some cavities, don't worry too much. Once absolutely dry, it will mummify and bacterial activity will cease, but specialist detritus feeders such as spider beetle may colonise them. For this reason, treat finished skulls as you would skins or fur clothes - protect from damp and condensation, and inspect them regularly for infestation. What do you think ? Did you try any of this advice ? Have you experience to offer ? Email me from Sue, USA " . . . My preparation methods are almost exactly as you describe for maceration. I simmer in a weak peroxide solution to whiten. To get most of the meat off, I set the severed heads outdoors in a cage (affectionately known as the "box 'o death") during warm weather. The cage is tied to a tree to prevent bears from dragging it off and lined with a fine mesh screen to prevent loss of teeth. The only problem I've encountered that I cannot explain is that sometimes teeth turn purple.I've seen it in raccoon and bear. Nothing removes the stain and I don't know why it's there.I sometimes see it even as the head is rotting outdoors. . . " from Patrick Barriere, French PhD Biologist " . . . STAINING : I have also observed such stains due to coloured bacteria which appear in anaerobic conditions underwater (maceration), or when the skull is left outdoors. In the first case, the stain can be removed by rapidly putting the skull in Javel (bleach ?) solution. In the second case it may be very difficult or impossible to get off, so always try to macerate the skull underwater if a natural treatment is favoured. BOILING : I never boil skulls because it fixes fat in the bone, and a few years later the fat migrates to the surface, making it black and greasy. ENZYMES : I have tried "Papaine" and have had bad results. You have to heat it, and this causes a very bad smell, maybe worse than maceration. Also, the teeth fall out and small skulls may disintegrate. On medium or large skulls you have to use a large volume of hot concentrated solution because of loss of activity of the enzyme, so I disagree when you say "a small quantity of water would be ideal" IN MY EXPERIENCE : The best methods are dermestid beetles for small skulls, and maceration for medium to large ones. If you must boil them, let them macerate in water for a week first. I am against bleaching as it removes the character and natural colouring of bones. Also, bleach may make tham brittle.I recommend wood glue (PVA ?) for teeth, as it can be undone with water, and does not stain . . ." from Sheila, zooarchaeologist, S England ( Editor's note : Sheila is perhaps more interested in cleaning whole skeletons rapidly than aiming for "perfect" results with skulls only. ) " . . . Composting is very good for large bodies especially if you don't have time to do much to them - it is possible to do nothing other than open them, but more preparation speeds the process. The compost bin has to be a good solid wooden type with a secure lid against scavengers and should be active or made so by adding straw, manure etc. That is how I prefer to do deer and anything biggish that is already smelly. Maggoting is best kept for medium mammals and birds, especially if already started down that route. After the body has been left to its own devices you pour boiling water on it and sieve out the bones - this and all my methods are tidied up with enzymes - see below. Small birds and mammals need to be boiled in a bag made of old tights or netting so that you don't lose any small bones. Prepare them first or deflesh when cooked. ENZYMES : My methods then require soaking in commercial neutral buffered protease, preferably at blood heat (e.g. use an aquarium heater) - very smelly after a few days. The body is then washed over with hot/boiling water, still in the bag or through a fine metal sieve. The result is pale brown - if bleaching is required then use Ecover laundry bleach from the health food shop. The commercial enzyme is very expensive (£300 for 25 litres) so you may have to make do with washing the bones in detergent. The only household enzyme I would use is Biotex, other washing powders are alkaline and can cause crumbly bones as well as chalky deposits . . . " From Meg, USA I cleaned an old mouse skull with a mixture of 1 part water to 1 part hydrogen peroxide (the kind you buy at the store to clean cuts). I left the skull in the solution until all the tissue came off (it took about a week or so). After it was clean I rinsed it in water and let it dry. All the teeth stayed in and the skull is still intact after 5 years. I don't think I would try this on a cow skull but it worked well on the mouse skull.
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