[NHCOLL-L:2042] Re: Preparing bones for display

[Sean Barry]

On Fri, 15 Aug 2003, Jody Ullman wrote:

> A bear skull has been donated to the museum, but needs some work on it
> before it can be ready for display or use in programs.  We do not have a
> person on staff who is familiar with bone prep, so it has fallen to me
> to figure this all out.  I have searched the internet and have found
> conflicting answers to the questions

> 1. How do you degrease the bones?
> 2. How do you whiten the bones?
>

I'd try to arrange with an established vertebrate museum to clean and
degrease the skull for you (maybe in exchange for some service you could
provide).  It's hard to set up to do just one skull to professional
standards.  But, if you insist, large mammal skulls are usually cleaned
by:

1.  Removing as much muscle mass as possible by dissection

2.  Extracting the brain tissue, dissecting away the eyes, tongue, etc

3.  Boiling (simmering, actually) in a mixture of water and mild detergent
or (better) water and clear household ammonia (fume hood).  Immerse the
skull in the room temperature solution, heat slowly to a slow boil, reduce
heat and simmer for an hour or two.  The ammonia-water combination works
best and fastest.  Let the skull cool in the solution, clean off the
remaining soft tissue in a stream of water--use toothbrushes, toothpicks,
probes, a dull knife blade, fingernails, whatever it takes.  Be sure to
clean out foramina (holes), pull out the teeth (they'll be loose), do not
damage the turbinate (nasal) bones.  You'll have to flush the nasal cavity
out with a hard stream of water, probably repeatedly, to remove all the
soft tissue.  Return to the pot and simmer again as necessary.  Bear
skulls are usually pretty tight so it's unlikely to disarticulate (opossum
skulls are the opposite).  Don't overdo the boiling--it's possible to warp
some of the membrane bones.

4.  Air drying

5.  Degreasing by soaking in warmed organic solvent.  Most of the good
solvents are extremely hazardous.  Carbon tetrachloride is commonly
recommended in older texts and is actually the best bone degreaser there
is, but it's so dangerous that no one should use it unless s/he really
knows how to do it safely (as in is extensively and specifically trained
in handling chemicals that shouldn't ever be handled).  Methylene chloride
works pretty well and is somewhat less hazardous.  Some preparators
suggest white gas (Coleman camp fuel) which is flammable and toxic
besides, and not very good at dissolving grease.  Check with museums to
see what they're using these days.  The bones are degreased when they dry
immediately in air--if drying takes a while, there is still grease in
there, and there are other indications of residual grease too.  This is
the trickiest and most dangerous step but it's also the most important to
do well and it's the main reason why you should seek a professional
collaboration.

6.  Thorough degreasing usually leaves the bones pretty white, but if you
insist on more, soak for 5-10 minutes in 3% hydrogen peroxide.  Remove the
bones from the solution and let them air-dry.  Rinsing is unnecessary
(the H2O2 degrades to H2O plus O2).  Don't overwhiten--overwhitened bones
look flat.  H2O2 bleaching is normally only done if the skull is to be
exhibited, but IMO even then it's usually not necessary.  Don't use
chlorine bleach--it makes the bones friable and doesn't bleach very well.

7.  Glue the teeth lightly in place.  The best glue that I know for bone
(unless the joint has to be structurally very strong)  is DUCO cement,
which dries clear, is impervious to humidity changes, can be pried apart,
doesn't take space in a joint if your technique is good, and is easily
dissolved with acetone.  Glyptal glue, commonly used in paleontology, has
many of the same properties but dries yellow-orange.

The best reference I've seen for all such processes is "Anatomical
Preparations," by Milton Hildebrand (1968, University of California
Press).  Most of the copies of this out-of-print masterwork are in
institutional libraries.

Sean Barry
*********************
Sean J. Barry
The Rowe Program in Molecular Genetics (mail address)
  and The Section of Evolution and Ecology
University of California
Davis, California  95616

Present address:

ENTRIX
7919 Folsom Blvd., Suite 100
Sacramento, CA  95826
(916) 923 1097