Drawing stuck to glass

Our Conservation Department has been asked to treat a large drawing
(25 3/4 x 38 1/2 inches) from our collection which which is stuck to
glass.  The drawing, done in 1980 by the late Aldo Rossi
(architect), was executed in graphite and coloured chalk or pastel
on translucent paper.  It was then coated with a transparent resin
which has become extremely darkened and discoloured, leaving it
streaked and disfiguring where it was applied more heavily and
formed pools and drips.  The resin appears to have embrittled the
paper.  The resin does not form a coating on the media--it has
penetrated and mixed with it.

The drawing was acquired last year, in its original frame, in which
it was sandwiched between two sheets of glass with a piece of
translucent white paper behind the glass on the back.  There are
many small areas across the whole surface of the front where the
drawing has become adhered to the glass.  There are also enough
areas where the drawing has already pulled away from the glass to
make it apparent that it would be easy to separate the drawing from
the glass--but not without damage to the drawing.  The resin has, in
those place, sheered away from the paper and stayed attached to the
glass, leaving bare white patches on the paper.  Wherever the resin
is mixed with media (in many places) it would take the media with it
when it sheered away from the paper.

I have spoken to the dealer from whom we acquired the drawing.  He
says it was not unusual for Rossi to glaze his drawings, spraying
them with fixatives and "other things".  I had wondered, given the
fact that the drawing was sandwiched between glass, if there was a
possibility that Rossi was using the resin to make the paper more
translucent, but the dealer does not think so.  He says Rossi just
liked a sheen on the surface.

I would like to hear from other conservators about their experiences
with drawings which have become stuck to glass.  Have you tried to
remove them? How and with what success?  Have you left them on
attached to the glass?  If so, how have you stored them to prevent
damage to the drawing should the glass break.  Although my first
instinct was to try to remove the drawing (perhaps using solvent
vapours to soften the resin) I am now considering just leaving the
drawing stuck to the glass, placing it on a rigid support panel
(perhaps attaching it temporarily to that support) and storing it
flat.

If anyone has encountered an Aldo Rossi drawing that was glazed in
this way, I'd be interested in hearing from them too.

Karen Potje
Chef du Service de la conservation/restauration
Centre Canadien d'Architecture


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                  Conservation DistList Instance 15:38
                Distributed: Tuesday, November 20, 2001
                       Message Id: cdl-15-38-017
                                  ***