Wednesday, March 6, 2013

Skulls and Skull Cleaning: Part II

In my last skull post, I didn't get to outline any of the techniques I use for actually cleaning and whitening skulls.

So, figured I should get to that now, for anyone interested.

Before I begin, I should preface this by saying that you should always wear gloves when handling animal carcasses (whether recently dead or otherwise).  I prefer nitrile gloves, but latex or rubber gloves would probably suffice, as long as you don't keep them and re-use them.  The risk of zoonotic infection from a number of species can be rather high, and it's just not worth the risk.  I wear gloves when I'm handling carcasses, heads or skulls (until the skulls are completely finished).  I even put bags over my boots if I'm using a foot to hold a road-killed animal still while sawing off a head for cleaning.  The saws, etc. are all cleaned with laboratory grade detergent, or a bleach solution.  I know some folks that scoff at this....but that's being reckless, in my opinion.  For interested folks, The Wildlife Professional recently published a good review on the risks that zoonotic infections pose to wildlife biologists (Yabsley, Fischer, Hernandez, 2012. The lethal jump from wildlife to humans. The Wildlife Professional, Spring 2012 Issue; pg 24-28).  There's some serious stuff out there, and a large number of wildlife biologists have died as the result of infection from such diseases.

De-fleshing:  This is probably the task that keeps most people from getting into cleaning skulls.  It can be incredibly messy and is often a stinky proposition.  Yet, there are a number of ways to go about removing the flesh from a skull you very fast and moderately quick and stinky....the other takes alot time, but one can avoid the associated stinky.

Let's start with the last one first: obviously one can just collect a carcass they find....set it in a place they know is protected from scavengers (and also away from any open windows) and let nature take its course.  This can be very effective....but there's always the scavenger problem.  Plus, it's easy for little teeth, etc. to fall out and get lost.  I've had some success avoiding this by first putting the carcass in a small container covered in screen (like a funnel trap used to catch minnows).  This technique worked fine for me with a weasel skull I cleaned many years ago....but another time was a total disaster with a mink skull I attempted to clean.  In the latter example, when I went back several weeks later, the skull had fallen to peices because I had waited too long to pull it.  Then there's the fact that this method takes a fair amount of time.

The next option is the very fast and stinky one: boiling the skull.  I've only ever been involved in an attempt to do this once.  It seemed to work very well (and was quick) but the smell was very strong (even though we were outside).  We used an old stock pot over a camp stove in a friend's driveway.  The flesh came off pretty well, although some of the brain matter became sort of hard, like cooked meat, inside the skull.  Thus, we had to try and pick it out through the foramen magnum (large opening at the back of the skull, where the brain stem exits and becomes the spinal cord).  Ultimately we were forced to bring the skull inside and use a utility sink in the basement to to start scrubbing/washing away the tissue.  Had we more time to let them boil, and also added some chemicals to the mix, the flesh may have just fallen off.  Yet, although it's quick.....the stink is an issue, it's also alot of messing around.  You don't want to boil a skull on your stove.  You'd fill your house with that stink!  You can do it outside on a grill or a propane stove, but that requires some work to set up and tear down.  You also have to clean that pot out!

You can see a recent post on Nature In a Nutshell where Alyssa incorporated this boiling method.

My preferred method of de-fleshing is to use flesh-eating (Dermestid sp.) beetles. 

These are actually relatively easy to get ahold of.  Some folks even collect their own from around carcasses found in the wild.  I prefer to just have them purchased from a biological supply company (such as Wards Scientific).  They are fairly easy to culture.  We have a colony at the university that is housed in a 10 gallon fish tank.  We have a sheet of glass over the tank (slightly cock-eyed so that a sliver of air can get in).  Because the room we keep them in gets a tad cold, we also put a heat lamp over the tank.  When you start the may require adding a few paper towels for them to hide in....but other than that, they don't need much.  You just have to throw them dead things every once in a while.  The number of beetles in your colony will dictate how quickly they clean your skulls.  The more you feed them, the bigger the colony will get.  But, a large colony can clean a fully-fleshed skull in a week or less.  For example, a week ago I put four smallish heads and one medium-sized head in the colony and they came out today free of tissue.

Some points to consider about Dermestids
  • If they escape....they may attack taxidermied specimens, or skin collections!  We've had this problem in the past.  One way to keep them in the tank is to rub vasoline around the upper edge of the glass around the tank.  The glass lid we use also makes a tight seal, which helps keep them inside (but we still have to leave a little crack for air).  We also keep our colony in a back lab under a fume hood (they stink!).
  • As they eat and excrete they create alot of fine particulate debris.  This can build up in the tank. If your skull happens to get a bit buried in that fine debris the Dermestids don't seem to be adept at getting underneath to clean flesh off the buried surface.  So I have to go in and rotate the skulls every so often.  It might help if we put some sort of grate in the bottom, so the skulls rest on top and the detritis falls through....but we haven't done that yet.
  • They wont eat hair or feathers.  So...those will build up quickly in the enclosure (we usually remove as many as we can before putting a carcass in the colony for cleaning).

But....the Dermestid colony does a good job.  Plus, I can put a head in and not worry about it getting damaged by the elements or stolen by a scavenger.....and I don't have to stink up the house or ruin a good stock pot from boiling heads!

De-scenting: There are a few steps I take after removing skulls from the Dermestid colony to reduce the smell.  Seems like no matter how long you leave them in the colony for, the stink of carrion is still pretty strong.  I find that sometimes eliminating that stink just takes the skull dries out over time, the smell goes away.  But, to help it along, I take these extra measures. 

First put the skulls in the freezer overnight.  As much as anything, this also helps kill any small Dermestid larvae that may be hanging around (can't have those escapees getting on the skin collection!).
The next morning, I remove the skulls and let them warm up a bit.  Then I go through a two-step cleaning process.  I first put the skulls in a strong bleach solution (90%) for a short amount of time, during which I check them frequently.  The amount of time I leave them in for varies (5 to 30 minutes depending on how things look).  Some folks will recommend you never use bleach on a skull, and I can't fault them in their logic.  I wear rubber gloves and frequently remove the skull to check on how it's holding up (paying particular attention to the lower jaw to make sure the two mandibles are not starting to separate).  But, basically I find you can't beat the bleach for really reducing the smell.  Plus, the bleach helps sanitize, in the off chance there's a disease-causing agent hanging around somehow.  Basically, so long as I watch the skull carefully, the damage is not noticeable (in fact, I've never noticed any serious damage to my skulls from the bleach solution).
After pulling them from the bleach, I rinse them thoroughly for 5 minutes or so with water.  I then put them into a strong ammonia solution (90%).  I leave them in this for about the same amount of time as the bleach, again making sure to check on them frequently. Once I feel they are as good as they'll get, I rinse them in water again.

The next step is to let them dry for a few hours.

Whitening: I've used two methods for whitening skulls.  First, I've just set the skull out in a sunny spot for a few weeks to let nature take it's course.  Usually the sun really helps whiten the skull, but this takes time.  Also, if it's a little skull, it could get damaged by the elements.  So I employ an alternative method told to me by a friend who used to do taxidermy.  It requires two ingredients: chalk and peroxide.  However, not just any chalk will do.  It has to be magnesium bicarbonate, which is chalk often used by weight lifters or rock climbers for helping get a grip.  I found a nice sized container at REI.  You also can't use your run-o-the-mill peroxide.  You need a special type of peroxide called "40 Peroxide" that's usually avialable from a beauty supply store or a hair salon supply store.

The peroxide and the chalk must be mixed together to form a sort of paste. I usually do this in a plastic cup.  I next spoon this paste over the skull.  It has to rest in place and dry on the skull, so the consistency of the paste must be such that it doesn't just run off of the skull.  You also have to get it in all the cracks and crevices.  Sometimes this requires back-to-back treatments. 

After the paste is in place, I let everything sit and dry at least overnight....sometimes for two nights.

Once the paste is completely dry, it's a matter of simply knocking and brushing it off.  I try to knock the large chunks onto a plate, as I've found I can re-use the chalk.  Then I take a fine bristle brush and lightly scrub the chalk off of the entire skull surface.  I also usually wear gloves as the powder can burn alittle if you brush it all over your hands and hold the skull for a while (especially if your fingers also somehow get damp).

Once the dry paste has been completely brushed off, it's a matter of using super glue to make sure all the teeth, etc. stay in the right place.  I also use glue to secure the seams between the different major bones in the skull (i.e., the frontals, the parietals, etc.).  Note that there still may be some stink (particularly from inside the brain case).  I try and reduce this further by spraying Krylon Clear Coat into the brain case several times.  Even that may not completely do it, and the smell may only go away with time.

The final product looks pretty good and creates a nice teaching specimen.

See the comparison below.  On top is the picture of the skulls right out of the ammonia solution (they are a little wet, which makes them darker than usual).  Below that is the end result after the paste has dried and been brushed away.


  1. Nice post! When I was in high school, I boiled a skull in my Mom's kitchen. To cover up the smell, I put some Pine-sol in the water. Hours later, when she got home her only comment was "Thanks for cleaning the kitchen." :)

  2. That's priceless!! Put a smile on my face, for sure.

    Did the skull turn out ok?

  3. Hey Trailblazer, loved this post! Definitely some great info for skull lovers. I've cleaned some of my skulls that I've found, but would really love to start up a dermestid colony. For some reason my wife won't let me! Could you please talk to her about that? :)


    1. Ha! I'll see what I can do.... Can you set it up at school?

  4. This is an AWESOME post. I've dabbled in skull cleaning, and have never been able to get beautiful white skulls. I have a coyote, gray fox, and porcupine that have been waiting to be done. Have you ever kept the dermestids outside during the summer? I'd be interested getting a colony going, but I don't have a hood in my house :)

    1. Thanks, Alyssa....

      I've never tried to keep a colony outside. The difficulty would be making sure you find a place that is protected from the elements. They would over-heat and die in any place that gets direct sun. Also, the right enclosure would be hard. They need some air flow....and if you use a fish tank with a screen top, any rain would get in and collect....potentially drowning your beetles. So, you'd almost need some sort of screened enclosure...and I think alot of the small larvae would be able to get out of that.

      Isn't there someplace at your college where they could set up a colony? (a store-room, or un-used lab space?).

  5. I am bookmarking this post. I need to try this someday. This past spring, I found two complete bobcat carcasses, skulls included. I would have loved to have prepared their skulls to keep. (but I was also a little afraid to handle them due to the possibility of plague). Anyway, thanks for the detail!

    1. Hey KB!

      Glad you found the post useful!

      Yeah, plague is nothing to mess about with, as you know. If they had been dead awhile, the fleas should have moved on to find a new host (they don't hang around too long after the body goes cold). Yet, I have no idea what a "safe" time post-mortem would be!

      I suppose you have so many coyotes, etc. around that those carcasses would be gone in no coming back to the spot later for the skull wouldn't work (?)

  6. Hi, I'm hoping you can help me out with some expert advice :)

    While at Tygerberg earlier today I picked up a great weasel skull (I'll do a blog post on that soon). The skull is in very good shape (at least I think it is) and I'd like to preserve it for as long as possible. I'm even thinking of using this to start my own collection. I'm not too concerned about the colour (I like some natural colours to show), but I would like to keep it intact. The skull is very small (about 5cm long and 2cm wide) and still has the lower jaw and teeth perfectly in tact. There is no flesh/skin/brain on it that I can see, it's just a little "dirty".

    I'm concerned that it might break apart if I use strong chemicals. Or it might start falling apart after a year if I don't preserve it. What would you recommend I do/use to preserve the skull intact (teeth, jaw, etc.) for as long as possible? I've read about spraying it with a varnish finish but will this not give it a very superficial/unnatural look and since the skull is so small some detail might get lost?

    If I don't treat it in any way, won't the bone decay naturally over time? (Should the skull be stored in a dry place?)

    Thanks for these posts, it gave me the confidence I needed to try this out for myself and possibility even start my own collection :) I might even start scavenging road-kill soon...


    1. Hi Henry!

      Thanks for reading and glad you found these posts useful!!

      I wouldn't consider myself an expert....I've never prepped specimens for big-time museum collections, etc. I've only prepped specimens for small university collections, etc....nothing to extraordinary. are my suggestions: if you don't have any issues with scent or the color of the bone....then it's a matter of first rinsing it carefully. You could always dip it in a very weak bleach solution....10% or so...for 10 or 15 minutes, just to make sure it's sanitized (up to you). Just have to keep your eye on it to make sure nothing starts falling apart (again, some will recommend against bleach at all costs, but I have not had major issues with it, so long as I'm watching). You could also use plain old peroxide for the same purpose...although both might also "whiten" the skull a bit, which you may not want. If you do this, just make sure you thoroughly rinse the skull afterwards to insure all of the chemicals are gone.

      After it's been rinsed, I would just let it sit for a while (day or so) to make sure it's dry. Then, I'd take some super glue with a fine nozzle-tip....glue all the teeth into the sockets (no need to remove the teeth first, just make sure the glue gets down into the seam between the tooth and mandible bone). You may have to watch it to wipe up any drips. Then I like to take that same super-glue and run a thin line along most of the major seams in the skull (between the large bones surrounding the brain, the cheekbone, along the center of the snout, etc.). I also like to put glue in the front of the lower mandible (about where the "chin" would be) to keep it together.

      Now...some folks will next use a lacquer of some kind to seal up the skull and protect it (they dip it right in and hang it to dry). I'm thinking of something clear, like a Polyurethane that you'd coat a wooden floor with. This shouldn't change the skull's color (provided you get clear polyurethane), and will protect it....but it will give the skull a shiny appearance. I've also used Krylon brand spray-on clear coat successfully, just had to spray on multiple layers (it's alot cheaper than polyurethane). Yet, I've never been concerned about how shiny the skulls looked....(and it sounds like you don't care for that shiny appearance...right?). So, you *could* try to use a Krylon spray-on clear coat that is "matte"....that might give it more of a dull bone-like texture/appearance? I think MinWax also makes clear coat spray-on polyurethane that is "matte". Perhaps something water-based will be better (some have suggested that an oil-based coat will yellow over time...but I have not experience with that).

      Having said all of this, I think with some super glue on the teeth and seams, the skull will last for years and years. I have skulls that have not degraded over time with only some super glue holding teeth/seams long as they are kept indoors and out of the elements.

      Keep in mind that mine are only years old, not decades old. The right coating may help it last for generations (?)....perhaps The Codger has some ideas on this, given his museum experience. I'll bet if you posed the question to him on his blog, he'd have a good answer.

      Perhaps others have comments on this....

      At any length, I hope this helps!!

      PS...scavenge that road kill! Just be fore-warned...the roadkill specimens often have damaged skulls (and it may not be obvious until all of the flesh is removed). Also, keep in mind that some regions require special permits to collect "salvage" like this. I have no idea what the laws are in south Africa....but I have to have a permit with the local regulatory agency to collect roadkilled animals as specimens.

      Good luck!

    2. Thanks for the help and quick response! I think I'll get started on this right away :)

    3. Good luck! Can't wait to see how it turns out!