I have cleaned several bear skulls, some by boiling and one with dermisid beetles. I soaked them in a degreaser rinsed them and then put them in 35% peroxide mixed 50/50 with water. I then pull them out and rinse them and let them dry and spray a clear laquer over them to seal it. A week later I found that the canines had cracked. Why did they crack and how can I fix them? THANKYOU
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Once cracked there is no way to fix them. About all you could do would be to try to hide the seams with an epoxy filler like smoothout.
Mammal skulls present different challenges for cleaning because of the teeth than the other vertebrate groups. As far as I have noticed though, the trick is in the drying and boiling procedures. I have only done a couple thousand mammal skulls and have not quite refined my technique.
There is a recent book published that primarily addresses skeletal problems stemming form work towards a PhD dissertation by Dr. Stephen Williams now at Baylor. The book "Destructive Preservation" deals with the problems in preserving mammal bone material for Museums, and costs $160 or so, printed in Texas but available from I think Goteburg Sweden. You can see a review in the most recent Collection Forum (Journal) published by SPNHC (Society for the Preservation of Natural History Collections. This work addresses field preparation, degreasing, drying, and storage of bone material - primarily humidity.
I did one scientific paper with Stephen back in the mid 80's using Artibius (bat) skulls and measuring types of field preparation and cleaning and measuring teeth cracking. Send me your address and I'll send a reprint but it may not be pertinent to your problem. I am thinking about testing some new techniques on drying teeth to prevent canine teeth cracking using Raccoon skulls.
Without seeing the exact proceedure you used for cleaning the Bears skulls I would guess that the problem stems from the Humidity you had them in while drying - or subjected them to after they were dry. The dentine on the outside of the tooth dries differentially from the inside of the teeth. I THINK that if you dry the teeth very slowly you can lessen the chance of craking. This can be from either doing it when the humidity is high (summer), or partially covering the skull and slowing drying. If there is a drastic lowering of the Humidity after the skull is fully dried this can also cause cracking. I prepared a Tiger Skull two years ago, had it completely "dry" for a couple months, but had it stored in my customized bugroom with a form of humidity control. I took it home a few days prior to transfer to the Zoo, a CA-CHING, the canines cracked because of the extremely dry humidity of my house (Radiator heat and wood stove).
When the teeth crack almost instantly upon drying - this is probably caused by too quick of drying. If you slow drying down it can dry without damage, BUT the skull must be maintained with humidity about 40% at room temperature, 50% ideal.
You may be able to slow cracking of canines by removing the teeth of bears and filling with pourable urethanes or hot glue, but this does not work with smaller teeth of canids, mustelids, or Chiroptera. I have had deer incisors crack also, and I surmise that humidity is the culprit.
Humidity also causes many problems to fully mounted animals. Dry Preservatives work down south much more efficiently than in the Northern Climbs. I would predict if a dry preserve deer head would be shipped north for the winter multiple cracks would appear where there were none before - kinda like drywall seams.
I hope I helped, but feel that I have rambled on too much.
The Taxidermologist