Fossils

Dominique Rogers <do [at] pepin__demon__co__uk> writes

>I am looking for alternatives; waiting for them I am back to the
>old cellulose nitrate that yellows, and will fail in 100 years or
>animal glues that yellow shrink and will fail in 300 years given an
>adverse environment but they stick and are easy to reverse!
>
>I have successfully glued mammoth bones with cellulose nitrate it
>will yellow and probably will fall apart eventually.

Now perhaps it is my turn to risk the ire of some:

My senior thesis some years ago was about cellulose nitrate as the
earliest synthetic plastic.  It has been around since the late 19th
century, and has changed little.  Its most remarkable properties as
an adhesive are hard to duplicate.

However, knowing its chemistry, I personally can not advocate its
use on any objects except the most robust and inert and only as a
last resort.  It is an inherently unstable material, and as its
volatile plasticizer is lost, it tends to become even more so.  Even
under good conditions, the reactive nitrate groups will split off
from the long chains.  When they do, if there is any water vapor
around, nitric acid *will* be formed.  Any materials that are
sensitive to acids (such as ivory, bone, paper, or metals) should be
protected from contact with this material.

Granted it is in small quantities, and probably will not adversely
affect ceramics, but I would have to think long and hard before
employing it at all.  Perhaps there is some new research that has
reversed all previous thought on this subject, but until I read such
a study, I remain steadfastly prejudiced against it. Sorry if this
sounds harsh, but I have had extensive first hand knowledge of the
damaging effects of unstable cellulose nitrate.

(deep breath)

So what would I suggest?  I know PVA is out of favor for the same
reason (acetic acid), but on the scale of reactivity, I think I
would prefer it over nitric acid any day.  Another alternative is
polyvinyl butyral which has had similar criticism, but it is soluble
in alcohol, resistant to water and has other desirable properties.
It is not my adhesive of choice, but I actually did use it
successfully to mend archaeological ivory when a tough,
alcohol-soluble resin was required and nothing else would do.

I invite other dialogue/comments on the subject.

Linda S. Roundhill
Art and Antiquities Conservation
Woodinville, WA 98072


                                  ***
                  Conservation DistList Instance 15:31
                Distributed: Wednesday, October 10, 2001
                       Message Id: cdl-15-31-003
                                  ***