Relative humidity control in microenvironments

I refer to the recent submission by Barbara Appelbaum in which she
states, in the discussion on raising RH levels in exhibition cases,
(low RH levels do temporarily embrittle books, but seem to have no
lasting negative effects, so for books, there is no point).

While it is true that *paper* will suffer no lasting effect when
subjected to a low RH if it is allowed to recondition to a higher RH
before use,  it is misleading to refer to *books* in this way.
Books are items usually made from several materials, some of which
can be damaged by being subjected to low RH levels.  In particular
there are vellum and parchment, which can react to RH changes
violently and unevenly, and leather bindings which may be in an
advanced state of degradation and/or dryness.   Since the rest of
Barbara's comment are very sound, I am sure this is a "slip of the
pen", but it is important to recognise, that with books, there are
likely to be other materials to consider.

John E McIntyre
Head of Preservation
National Library of Scotland
George IV Bridge
Edinburgh  EH1 1EW
+44 131 226 4531
Fax: +44 131 220 6662

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                  Conservation DistList Instance 10:11
                  Distributed: Tuesday, July 16, 1996
                       Message Id: cdl-10-11-003
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