Polyurethane wood sealants

I have seen wooden backing boards in display cases and storage boxes
treated with liquid polyurethane. Stretcher bars are sealed with
polyurethane also for the same purpose.

How effective is a polyurethane coating as a barrier for acid
migration from wood?  I would also like to know how long
polyurethane has been used for this purpose and if it is stable and
safe as it ages.

Zee-Young Chin,
Student in conservation
Avignon, France


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                  Conservation DistList Instance 18:41
                  Distributed: Tuesday, March 8, 2005
                       Message Id: cdl-18-41-008
                                  ***