Paintings on glass

Gary Saretzky <saretzky [at] rci__rutgers__edu> writes

>A colleague has miniature painted portraits on glass in cases
>similar to those used for daguerreotype, ca. 1850, with flakes of
>paint separated from the glass.  Does anyone have a recommendation
>for readhering them?  In case it matters, the images are colored and
>the glass is flat.

Back in 1987 I treated a couple of 18th century reverse-glass prints
at the Canadian Conservation Institute.  The adhesive I used, based
on the recommendations of Jane Down's adhesive research at CCI, and
Norman Tennant and Joyce Townsend's work, was Hxtal NYL-1. This was
based on the fact that the refractive index of the original glass
and that of the Hxtal were almost identical:  Glass: 1.520 to 1.530;
Hxtal: 1.5201 =+/- 0.0010

The other adhesives I looked at  were Epo-Tek 301, 301-1, 301-2.
These had a higher refractive index  and were considered
unacceptable.   The important thing to bear in mind here is that,
according to Tennant and Townsend: " For most practical purposes it
has been shown that a match of c. 0.01 can lead to an almost
invisible repair, and that a mismatch of c.004 can leave the break
or crack readily visible". (Tennant, Norman H & Joyce H. Townsend.
"The Significance of Refractive Index of Adhesives for Glass Repair"
, Adhesives and Consolidants. Preprints of the Contributions to the
Paris Congress, 2-8 September 1984, eds. N.S. Brommelle, E.M. Pye,
P. Smith, G. Thomson (London: IIC,1984), pp. 205-212).  The glass in
this case had a slight curve in it and various clamping techniques
had to be employed to hold it all together, and it was also
necessary to use small spots of cyanoacrylate adhesive to
temporarily hold the glass together before running the Hxtal into
the cracks.

More information about my treatment, together with an analysis of
the pigments found, a section on the history of reverse-glass
prints, and a discussion of the problems of consolidation, can be
found in: Tremain, David. "Reverse-Glass Prints: Their History,
Technique and Conservation", Proceedings of Symposium 88: The
Conservation of Historic and Artistic Works on Paper (Ottawa:
Canadian Conservation Institute, 1994), pp. 143-152. This is now out
of print, but a photocopy can be obtained from the CCI Library for a
nominal fee.

David Tremain
Canadian Conservation Institute
613-998-3721
Fax: 613-998-4721

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                  Conservation DistList Instance 13:33
                 Distributed: Friday, December 3, 1999
                       Message Id: cdl-13-33-001
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