Plexiglas

David Stevenson <dstevenson [at] cca__qc__ca> writes

>In one of our galleries, we mounted 3/16th inch thick acrylic plexi,
>measuring 96 inches x 29 inches overall, to a solid rectangular
>frame made of Medite board. This whole case is wall-mounted in
>'landscape' orientation. The show has now been mounted for less than
>two months.  We have checked the environmental records of this
>particular gallery since the show opened, and they show no unusual
>or extreme changes. The objects behind the acrylic plexi, gelatin
>silver photographs, show no signs of being affected by environmental
>changes.

The problem is undoubtedly dimensional change in the Medite.
Although the acrylic is very slightly hygroscopic, the dimensional
change you see could not be explained by change in moisture content
and you are clearly not seeing a temperature change that would
explain the problem.  The Medite, on the other hand, is very
hygroscopic, and a 6mm or even 8mm dimensional change in a panel
that size is not surprising.  Probably the Medite was very moist
when it was cut (probably in the summer?) and the painting process
would have added even more moisture. The panel has gradually shrunk
as it dried out in the gallery. The solution is to recut the
plexiglas now that the Medite has equilibrated with the gallery
conditions.  It will be reasonably stable in constant relative
humidity.

Van V. Wood
Smallcorp
19 Butternut St.
Greenfield, MA, 01301
413-772-0889 ext 104
Fax: 413-773-7386


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                  Conservation DistList Instance 25:24
                 Distributed: Sunday, November 13, 2011
                       Message Id: cdl-25-24-002
                                  ***