Relative humidity control in microenvironments

I assume that Ms. Gilderson-Duwe will receive many answers on the
question of increasing the RH in exhibition cases, but just to add a
voice:  I suggest (1) a reading of either Garry Thomson's book, The
Museum Environment, my book, Guide to environmental protection of
collections, or a number of others written specifically for
libraries and archives.  (I assume SAA must have a bibliography;
NEDCC can also probably help with bibliography as can any number of
archivists, conservators, etc.)  In teaching, I have seen how
difficult some concepts of RH are, so I spent a lot of time trying
to explain it in ways that non-technical people can grasp.

The main question is what is in the exhibition cases she refers to.
Low RH levels do temporarily embrittle books, but seem to have no
lasting negative effects, so for books, there is no point.  In
addition, if exhibition cases hold large numbers of closed books,
the amount of hygroscopic material they contain compared with the
volume of air would make the contribution of the silica gel minimal,
and tightly closed books are affected by ambient RH only extremely
slowly.  In addition, the use of silica gel either to raise, to
lower, or to buffer RH requires tightly sealed cases--if the cases
in question were not constructed with this in mind, the use of
silica gel might not accomplish anything.

The most important question might be whether whatever types of
objects are in the cases actually exhibit any symptoms that would
indicate ill effects from the RH levels they have been subject to
through the years. There is substantial technical literature on
aging and RH, but careful examination of the objects themselves is
still the place to start. Another way to answer this question is to
recommend strongly that the library have a professional familiar with
collections management issues consult.  The choice of consultant
would depend on what the collections are.  For a library collection
there are many knowledgeable people.  For a more general collection,
many conservators could be helpful. My guess is that an overall
assessment is needed.

Barbara Appelbaum

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                  Conservation DistList Instance 10:9
                   Distributed: Friday, July 12, 1996
                        Message Id: cdl-10-9-004
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