Consolidation of mud plaster

I am looking for advise on the consolidation of mud plaster. The
object in question is a skull from the Sepic River area. It is
covered with mud plaster, and the surface is painted red and white.

The skull was moved about two years ago from a tropical climate to a
dry one, and the mud plaster started crumbling. The surface paint is
also cracking, and detaching from the mud ground.

We have in our collection a mud plaster mask which had a similar
problem, and was consolidated with PVB. It is now over 8 years since
treatment, and it remains stable. At the time, according to the
file, experiments were made with PVA and Paraloid, but PVB seemed to
give the best results. However, the treated mask was not painted,
and I am concerned that in the present case, over time, PVB will
cause colour change in the white pigment.

I would appreciate any comments on the use of PVB as a consolidant.
I will also like advise on other possible consolidants, and possible
adhesive to attach the mud to the skull. Adhesives should be gap
fillers, because of the losses in material. I have in the past used
a mixture of Methocel and PVA emulsion, thickened with bentonite.
Any comments on this will be appreciated.

Smadar Gabrieli
Dept of Classical Studies and Ancient History
University of Western Australia

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                  Conservation DistList Instance 9:68
                  Distributed: Tuesday, April 2, 1996
                        Message Id: cdl-9-68-004
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