Removing lacquer from stained glass

I am working on a problem with a stained glass window from New
College, Oxford, UK.  The window is from 12th. Century (my guess,
but not important.)  It was removed during World War II, and placed
in storage, then replaced after the war (1946)  When the window was
restored and replaced (by Miss Joan Howson,) she searched for 'some
preparation that would protect the glass surface against weather and
chemical action.'  She was advised (by Sir. Holbrook Gaskell,) to
use either 'Brushing Belco' or 'another lacquer of finer and more
transparent texture.'

The window is now to be cleaned of this lacquer, and it is required
that the lacquer be identified sa a suitable solvent may be used. It
apparently originally came from ICI (paints division,) as a
'lacquer, Ref. No. 317-162,' which was actually sent under the
experimental Ref. No. SXD 552.  However, these numbers do not mean
anything to ICI paints as they are now, who return the answer that
they do not know of any product with that name.

Infra-red spectroscopy has tentatively identified this as a
cellulose acetate lacquer, which should be soluble in amyl or butyl
acetate, but the lacquer on the window is not.  I would be very
interested if anyone could identify the ICI product from the numbers
given above, or suggest a solvent for cellulose acetate aged in the
atmosphere for 50 years (and supposedly having undergone
cross-linking reactions.)

Any other info on the likely lacquers in use at this time would also
be greatly appreciated (polyvinyl acetate or shellac?) that could
have been used on this window.

Simon Hogg,
Imperial College
London, SW7 2BP

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                  Conservation DistList Instance 9:56
                Distributed: Thursday, January 25, 1996
                        Message Id: cdl-9-56-002
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