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Subject: Offgassing


From: David Thickett <david.thickett<-a>
Date: Monday, July 28, 2008
Eliz Alahverdian <alahverdian [at] adelphi__edu> writes

>We are working on an exhibit in which we are building a temporary
>support to stabilize a tapestry. We would like to use a wood frame
>support and would like to know which wood outgasses the least as
>well as which sealant should be used. We realize all woods outgass
>but are wondering what our best choices would be?

There is no absolute scale for off-gassing from woods as it depends
on a lot of factors such as sapwood/heartwood, time when the wood
was cut, was it floated, kiln dried etc.  If you consider ethanoic
acid the main problem (which it will be for cotton), then most of
the comparisons have placed beech and birch at the bottom end and
spruce not too far up. Regarding sealants, unfortunately the best
performing UK available sealant is no longer available.  Generally 2
part polyurethanes have performed best.  However each needs careful
testing as many are actually far worse for out-gassing than the wood
(at least in the short term (6months or so)). The frequently used
Dacrylate only significantly blocks formaldehyde, it has a minimal
effect on ethanoic acid and many other species.

David Thickett
Senior Conservation Scientist
Collections Conservation Team
English Heritage
1 Waterhouse Square
138 Holborn, London EC1N 2ST
+44 207973 3322
Fax: +44 207973 3209

                  Conservation DistList Instance 22:8
                  Distributed: Sunday, August 3, 2008
                        Message Id: cdl-22-8-001
Received on Monday, 28 July, 2008

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