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Subject: Relative humidity

Relative humidity

From: Randy Silverman <rsilverm>
Date: Wednesday, March 1, 1995
Karen Motylewski raises a tremendously valuable point about the benefits
of lower relative humidity levels on the permanence of library
collections.  Out in the arid American West in 1990 we conducted a
library-wide survey and found that 75.5% of the book collection was
printed on acidic paper, while only 1.9% of the paper was brittle enough
to break at two double folds.

These data were compared with similar brittle book surveys conducted
earlier at Yale and Syracuse University Libraries.  Those surveys
revealed similar percentages of acidic books--grouped by date of
publication--at all three libraries, but significantly higher
percentages of brittle paper in Connecticut and New York than in Utah.
The results of the study were published by Matthew Nickerson as, "pH:
Only a Piece of the Preservation Puzzle: A Comparison of the
Preservation Studies at Brigham Young, Yale, and Syracuse Universities"
in the library journal, "LRTS" (36/1, pp. 105-112).

Personal communications with Akio Yasue (1991-92) at the National Diet
Library in Tokyo, Japan, reveal observations of similar findings there.

Before jumping to conclusions when relying on real-time aging data from
the library stacks, a number of variables need to be considered such as
air pollution levels, the percentage of the collection that has resided
consistently in the environment in question, the date the HVAC system
was introduced, locations in the library that may have super-heated some
percentage of the books during the summers, etc.  However, these initial
findings seem to support Sebera's hypothesis that lowering relative
humidity is one way to slow down the deterioration of library material.

Other studies comparing identical titles aged in libraries located in
both arid and humid environments are needed to corroborate or disprove
these early findings.  Also, considerations about optimal storage
environments for library material must include non-paper media (vellum,
leather, photographic emulsions, etc.).  However, I agree with Karen;
25% RH seems to be ideal for library permanence (if we could, in fact,
achieve it!).  She is to be applauded for bringing this key issue to the

Randy Silverman
Preservation Librarian
University of Utah

                  Conservation DistList Instance 8:70
                   Distributed: Sunday, March 5, 1995
                        Message Id: cdl-8-70-001
Received on Wednesday, 1 March, 1995

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