Identifying UV filtering materials

I sometimes need to confirm that works on paper in our collection
are glazed with UV-filtering Plexiglas.  In the past, I would do
this by unframing the piece, and using an Elsec UV monitor to
measure how much ambient UV was transmitted through the plexi.  We
also use the edge colour of the glazing as a clue.  I feel that I've
found a much quicker way to do this, by using a UV light source on
the front of a framed piece in a darkened room.  In my quick tests,
the UV rated Plexiglas and glass samples reveal only a dark purple
quenching, and the artwork behind the glazing is made dull and
non-fluorescing.  Non-UV-filtering Plexiglas lets the paper and
matboards fluoresce naturally, with some slight purple shadow caused
by the modest UV-absorbance that is present in all Plexiglas.  If
this way of testing is conclusive, it would avoid a lot of unframing
and the stress that can put on both artwork and conservator.  Is
anyone using this method?  Or has anyone seen a flaw in this idea
that I've missed?

I can also send digital pictures illustrating what I'm trying to
describe to anyone interested.

Heather Hendry
Assistant Conservator
Yale University Art Gallery


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                  Conservation DistList Instance 18:8
                 Distributed: Wednesday, July 21, 2004
                        Message Id: cdl-18-8-001
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