Cleaning methods

Cleaning skulls and bones

There are many ways to clean skulls and bones. People often think that burrying and let nature do its work is the best way of cleaning skulls and skeletons. Another often recommended method is to put a dead animal on top of an ant's hill and wait a couple of days. In my opnion both methods are the best way to get rid of a good specimen and to end up in disappointment. In the next paragraphs I will explain something about cleaning skulls, at least how I clean skulls and some of my experiences with it.

I clean skulls and bones for over 45 years. In the early days of my collecting my mum was very helpful and after some disapointing experiences with burrying skulls she started to boil them. Not in the kitchen although she did some fresh specimens there, but on a camping stove on the balcony of our flat. A smelly business from time to time, but I still have some of those 'antique' skulls in my collection, and they are good. But boiling is not a satisfactory procedure after all: bills and fragile parts easily get damaged and sometimes skulls won't get clean, no matter how long you boil them.

Today I use other methods. I prefer macerating. It is a safe method; even the most fragile parts stay intact and skulls get perfectly clean. There is but one great disadvantage, it smells like hell. With some precautions this problem can be kept under control to a certain extend.
Since a couple of years I use a professional laboratory oven in which I can clean a whole series of skulls and skeletons in one time, so it smells only once in a while.

Step 1 Preparations

For good and quick cleaning it is best to remove the skin and as much flesh as you can. Sometimes you find completely dried and mummified carcasses. In such cases you better soak them a while before you start removing the flesh. Remove the brains by stirring the content of the skulls through the occipital hole and flush them out under the tap. It can be handy to use a large syringe to flush with force. I use a large syringe that was used to rinse peoples bladders. I always remove the eyes.
To remove the flesh I use different surgical tools, but the most important are disposable scalpels and a few types of surgical tweezers and surgical scissors.

Step 2 Cleaning the skull

Macerating in water

Put the bones in a jar with water and keep them at a constant temperature of about 35 to 40 degrees C. I use a laboratory oven for this, but ou can also put them on a warm spot outside (in warm coutries) or put it on top of the heating radiator.
After a day (or two) you should check the skull to see if the bill sheaths come loose and can be removed. This is the trickiest part of the process if you want to keep the bill sheath in good condition. Normally it takes about 24 to 48 hours before the bill sheaths can be removed, but with old and long dead specimens or when you macerate at low temperatures this doesn't work. Sometimes one has to loosen and remove the sheath carefully with a suitable tool. I use dentist's tools. Sometimes even this doesn't work and you have to live with a skull without sheaths or macerate it with the bill above the waterline. Cleaning the skull with a hot bleach solution is another option, see below.
If you don't have an oven or a 'bain marie' you can try cold water maceration. Basically the same process, but witout heating. In warm water cleaning is often a matter of just a few days, but in cold water it may take weeks or even months.
Sometimes the macerating process stops for no obvious reason: apparently all bacterial activity stops in one jar while in another everything goes on without a problem. To restart the process, boil the skull for a few minutes, clean the jar thouroughly and repeat the procedure. It helps when you put some water from another jar with active maceration to speed up the new maceration process.

The bill sheaths

After removing the bill sheaths you should keep them in the freezer or in alcohol until the skull is ready. If there is no alcohol or freezer available, just let hem dry, but the quality often falls back.

Macerating with washing powder

After removing the bill sheaths (never before because you can't get the sheaths off!) macerating with washing powder is a good method. Add a spoon of biologal washingpowder (with enzymes) to the water and keep the whole lot on a temperature of about 60 to 80 degrees. The enzymes do the macerating and after a few days all meat is weak and can be rinsed and brushed off rather easily. This method has a big advantage: the smell isn't so bad anymore.

The hot bleach solution

If you have a head that has become mummified or will not macerate and you want to keep the bill sheaths on, cleaning in a hot bleach solution is a good option. Soak the the head in warm water for a while until the remaining skin and flesh has softened. Remove the skin and as much flesh as possible and circumcise the bill sheaths carefully. Put some bleach in a jar and hot water (1:3) and stir with the head with the bill above the solution. The flesh will be 'eaten' by the solution fairly quick, so be careful.
Because the bill sheaths are of tougher material these will not get damaged immediately. Rinse the head from time to time to avoid damage to the bone and bill sheaths. Cleaning a skull with this method may take not more than 10 minutes.
Caution: The bleach solution is agressive, so be careful with your skin and eyes.
Before using this method I advise to try this a few times before with heads that are not important for your collection. There is always a chance of some damage to the bone.

Alternative way of cleaning

Boil as long as nescessary and remove the flesh by hand. As stressed before, skulls cleaned in this way easily get damaged

Final cleaning

After the maceration is completed and all flesh has rotten off you have to rinse all bones thourougly without loosing any of the smaller bones. Always (and when I say always, I mean always) use a sieve. After you have fished all bones out of the sludge (count them!) it is best to do a final cleaning in a hot bleach solution (1: 4). This removes all remaining flesh in less than a minute, desinfects and removes most of the stench. After that rinse with clean water and let the bones dry.

Step 3 Degreasing

Bones are often fat and need degreasing if you want them pure white in the end. There are some hight tech methods with a soxlet installation for instance, but normally people use white spirit, acetone or an ammonia solution. The use of a great degreaser as carbon tetrachloride (Tri) is not advisable because of its carcinogenity. The time the bones have to spend in the degreaser depends on the amount of fat and may take from a few days to several months with regular refreshing. After degreasing you can whiten the bones.
Caution: White spirit and acetone are very flammable, so be careful with open fire in the direct vicinity.

Step 4 Whitening

The best way to whiten the bones is with H2O2 or hydroperoxide in a 3 to 10% dillution. This may take from a day to a week or more.
Caution: Be careful with strong solutions because it burns your skin (and eyes) and can damage the bone. Bill sheaths may loose their colour when put in hydroperoxide, you better keep them off or above the water line.

Step 5 Glueing

After the bones have dried you may want glue the skull or skeleton together. I never have built skeletons so I can't give any advice on that. The glue I use for the skulls is ordinary white wood glue for indoor use. This is not water resistant, which gives you the possibility to adjust things after the glue has dried by keeping the skull a few seconds over hot steam and pushing the bones in the right position.

Peparing specimens when you are travelling and having no freezer at hand.

You will always find intresting things when you don't have the opportunity to do what is described above. In those cases you have to improvise a little bit. I tried several methods, but I'm satisfied most with the following procedure.
Always take some suitable tools, scalpels, pincers etc. with you. Just do what is written under Step 1, put the whole lot in boiling water for less than a minute and dry the rough skeleton or skull as soon as possible with a hairdryer, the blowing end of a vacuumcleaner or in the air.
If you have the opportunity to macerate for a few days at a sunny spot you can remove the bill sheaths before and keep them in alcohol. Once dry, wrap the skeleton in plastic foil (from the supermarket) and mail it to you home adress where a neigbour or friend can put the parcel in the freezer.

Nota bene

Apart from the right tools and equipment good results in skull claning is also very much a matter of experience.
If you need any advice you can always send me a message


Be aware that in many countries it is not allowed to collect dead birds or parts of birds, even when you find them dead on the beach or along the road. You may find that this makes no sense but in some countries law enforcement on this is a serious business. Picking up dead birds and sending skulls and bones home or bringing them in your luggage is at your own risk.