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Subject: Paleo-Bond

Paleo-Bond

From: Gregory Brown <gbrown>
Date: Friday, April 20, 2001
Diana Komejan <dandi [at] tallships__ca> writes

>Does anyone have any information of an adhesive called Paleo-Bond?
>Specific it has been recommended as a filler and adhesive for
>Mammoth Ivory. Is this an appropriate adhesive?

Paleo-Bond is one of a very large number of proprietary cyanoacrylate
adhesives ("super-glues"), nothing more, nothing less.  All the
caveats found in conservation literature regarding cyanoacrylates
apply.

Cyanoacrylates in general suffer from several disadvantages:

    1.  A plethora of proprietary formulae.  Formulae can change
        without notice, additives are not disclosed, and their
        effect on the long-term stability of the object are unknown.

    2.  Essentially non-reversible (at best, reversible with great
        difficulty)

    3.  Reactive with some elements/minerals commonly found in paleo
        specimens.

Their advantages are rapid set time, and extreme strength.  In some
cases, these properties can also be listed as disadvantages.

While there *may* be a few legitimate uses for cyanoacrylates in
paleontology, I would be extremely reluctant to use it as a "filler"
and adhesive for mammoth tusks. Mammoth tusks are among the most
difficult objects to stabilize because of their structure of
concentric rings of dentine which shrink differentially as they dry
or are exposed to fluctuations in humidity and temperature.  These
shrinkage forces are extremely powerful and act to widen the gaps
between dentine rings.  Cyanoacrylates are extremely strong
adhesives and act to prevent the gaps from widening.  The result can
be disastrous, since both these forces can easily exceed the
strength of the dentine itself.

Cyanoacrylates and other powerful adhesives (such as epoxies) have
been used in similar situations with perfect success, but these
chance successes can not be reliably predicted.  Roulette is a game
best played with a wheels and marbles, not guns or mammoth tusks!

Generally, it is wise to use an adhesive that is actually weaker
that the object upon which it is used, especially if dynamic forces
are still in play.  Better that the adhesive fail than the object.
Perhaps a more flexible adhesive/filler based upon a reversible
polymer such as polyvinyl acetate, combined with good physical
support for the specimen, would be a better way to go.  In this
case, an often cited "disadvantage" of PVAc (low glass-transition
temperature and tendency to "flow") could actually be an advantage
by imparting some degree of flexibility to the tusk.

Disclaimer:  I am not a conservator, nor do I play one on TV.

Gregory Brown
Chief Preparator
Vertebrate Paleontology
University of Nebraska State Museum


                                  ***
                  Conservation DistList Instance 14:56
                  Distributed: Monday, April 23, 2001
                       Message Id: cdl-14-56-009
                                  ***
Received on Friday, 20 April, 2001

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