Fossils

Christine Ianna <christinei [at] qm__qld__gov__au> writes

>I have been approached by a member of our Vertebrate Fossils section
>requesting advice on alternatives to PVA for consolidating and
>adhering large fossil specimens even smaller ones for that matter.

As a Vertebrate fossil preparator, I think I can offer some
assistance on this question.  But I would like some clarification
first.  Which type of PVA are they currently using?  As an aside,
and a general request, can PVA's and PVAC's be referred to by brand
name on this list?  There are several types and they have different
properties.  In reference to either the PVA or the Paraloid--How are
they using it?  In which solvent?  And at what thickness?  What were
the shortcomings?  I prefer to use Paraloid (Acryloid) B72, at 1:1
beads to acetone,  mainly for adhering small to midsize specimens. I
don't really find that it has the strength  for really large
dinosaur-type bones.  For those we've had to stick with epoxies.

And, although, I sometimes use it, I don't really find it acceptable
as a consolidant for smaller material. It is too thick/sticky and
even at very low ratios leaves something of a shiny film on the
specimen.  Conservators, please remember that preparators are
usually looking at specimens through a microscope.  Although, I want
to stress I do not consolidate specimens unless absolutely
necessary.  It will indeed preclude certain kinds of testing, even
on fossils.  Given the sophistication of testing today, we have no
idea of the possible information that may be lost.

The two other products currently most used as adhesives/consolidants
by preparators are the Butvars, B76 or B98, and Vinac B15 (PVAC).
While I have more experience with Butvar, both seem, to date anyway,
to work well and hold up reasonably well over time.  If any of you
have any insight or information about these or other products I
would like to hear it.  I, too, have a long-time interest in
adhesives.

And while I'm at it, someone in Conservation DistList Instance:
15:30 Tuesday, October 9, 2001 also replied to this question and
stated that they will use cellulose nitrate. Um, please don't use
this on fossils.  (Although, I did hear that the plastisizer in HMG
is different and that it lasts well, I'm still not sure).  I deal
daily with fossils glued together 100 years ago with cellulose
nitrates and with fossils glued together 10 years ago with cellulose
nitrates (Duco).  In other words, I spend a good portion of my life
regluing failed joints.  If these are not readhered important
information can be lost.  So, whenever possible, I use Acryloid
(Paraloid) in the hope of avoiding this loss in the future.

I hope that this ranting is helpful, it'd be great to be put in
contact with  your preparators, this is just the kind of
conversation that we preparators love.

Marilyn Fox
Preparator, Division of Vertebrate Paleontology
Peabody Museum of Natural History
Yale University
170 Whitney Avenue
New Haven CT USA 06511


                                  ***
                  Conservation DistList Instance 15:31
                Distributed: Wednesday, October 10, 2001
                       Message Id: cdl-15-31-004
                                  ***