Crazing of acrylic sheeting

About two years ago we discovered that a group of about 20 large
lithograph prints which had been framed about 3 years before
exhibited a continuous, translucent, dull white appearance which we
first feared was mould growth on the window mount. These prints were
trap mounted with broad areas of mount board at the periphery of the
prints and the white was only present in the area of the mat where
it contacted the acrylic sheet.

On disassembly, it became apparent there was no mould, but rather,
the acrylic was minutely crazed where it came in contact with the
mount board. No damage to the board or the print was or has since
become apparent.  We used Canson buffered board in white and ivory
during this period of time . The glazing was 3 mm ultra violet
absorbing clear cast acrylic which is always supplied by the same
retailer.  Our supplier has confirmed that her has supplied
different brands at different times due to changing price and
availability and we had noticed variations in the protective
wrappings of the sheets from time to time.  We also checked new
supplies and caught a few deliveries which were not in fact u.v.
absorbing which were returned.

We sent samples of the crazed acrylic sheet to our supplier who in
turn contacted his various suppliers and have been told its all a
mystery, but that sometimes too much styrene is used in the
manufacture and this can cause crazing.  Since our first discovery,
we have occasionally encountered additional examples on prints in
various media and photographs and have simply replaced the acrylic.
No damage to the mount or work of art has yet been noted.

My suspicion is that there may be a reaction with long term contact
of buffered board with some types of acrylic sheet.  It would be
considerably worse if buffered board reacted to all cast acrylic as
we have mounted a huge number of works in this board. Fortunately,
most are stored in Solander boxes and these mounts would only
briefly be in contact with acrylic sheet when they were occasionally
displayed in stock frames.

Has anyone had a similar experience, has any damage to works or
mounts been documented and has any explanation been demonstrated?

Thomas Dixon
Chief Conservator
National Gallery of Victoria
Fax: +61 3 92080246

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                  Conservation DistList Instance 10:53
                Distributed: Thursday, December 5, 1996
                       Message Id: cdl-10-53-006
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