Plaster adhesive

Margot Wright posted a query regarding a white mystery adhesive on
Egyptian alabaster and calcite bowls. This may well have been, as
she suggested, plaster mixed with casein. However the following
water-insoluble adhesives have also been encountered on Egyptian
artefacts:

    Gesso
    Lime putty with linseed oil
    Gutta percha mixtures.

Some water-insoluble adhesives respond well to Industrial Methylated
Spirits which has a few drops of ammonium hydroxide added. Distilled
water mixed with equal parts of acetone or of ethyl alcohol can also
be useful.  These generally do not dissolve the adhesive but act on
the interface allowing the rather dense adhesive to be picked off
with a dental tool, plastic or wood probe or a polished scalpel
blade.

Adequate safety precautions regarding breathing and skin protection
should be observed, even for solvents of relatively low toxicity.
Good luck,

Helena Jaeschke
Archaeological Conservator

                                  ***
                  Conservation DistList Instance 11:67
                 Distributed: Friday, February 6, 1998
                       Message Id: cdl-11-67-002
                                  ***