Relative humidity

The only thing I would add for readers of this list to my following
response to a query on the Archives List is (if you haven't already) to
take a look at the "Preprints of the Contributions to the Ottawa
Congress [IIC], 12-16 September 1994: Preventive Conservation Practice,
Theory, and Research,"  particularly Erhardt and Mecklenburg (p. 32).
See also any of Stefan Michalski's papers on the subject of relative
humidity, notably "Relative Humidity: A Discussion of Correct/Incorrect
Values," (I think this is in the preprints of the Washington IIC (?)
Conference in 1993 (?), but I've lost the full cite).

I've wanted to put my opinion about this out on the table for a long
time, and just got the courage.  Ok, shoot at me.

    Date: 27 Jan 95
    From: Karen Motylewski <nedcc [at] world__std__com>
    To: Paul Gifford <GIFFORD_P [at] CROB__FLINT__UMICH__EDU>
    Cc: Multiple recipients of list ARCHIVES <ARCHIVES [at] MIAMIU__ACS__MUOHIO__EDU>
    Subject: Re: Relative Humidity

    >I'm aware that an R.H. of 70% or more is apt to cause fungal growth
    >and rust staples and paper clips, etc.  But if the relative humidity
    >in this new building remains relatively constant and within the
    >range of 55-60%, is there any risk to paper in the collection?  Is
    >the 40-45% more of a practical compromise than an ideal?

    I refer you to "Isoperms: An Environmental Management Tool," Donald
    K. Sebera, Washington, D.C.:Commission on Preservation and Access,
    16 pp. The Commission's address is 1400 16th St. NW, Suite 740,
    Washington, DC 20036-2217 (202-939-3400). The short version is that
    moisture and temperature interact in the deterioration of paper (and
    other media).  The hotter and moister, the faster the damaging
    chemical processes, lead by acid formation.  Lower the temperature
    at the same RH, and deterioration is slowed (slightly to greatly,
    depending on the temperature); lower the RH at the same temperature,
    and the same is true.  Sebera has constructed a graphic diagram to
    model the quantitative impact of these alterations in environment.
    The value 40-45% RH is better than 50-55%, but it, too, is a
    compromise (see William K. Wilson, "Effect of Relative Humidity on
    Storage and Use of Records," Abbey Newsletter 17(7-8), p. 91).  Most
    paper collections would be better preserved at about 25% RH.  Below
    that value some crosslinking of cellulose molecules appears to
    occur, and there may be embrittlement of adhesives, leather, and
    other components.  A decision about the value to be maintained for
    library and archives collections is a balancing act between human
    comfort, energy costs, equipment capability, and preservation (not
    necessarily, but often, in that order).

Karen Motylewski
Northeast Document Conservation Center
100 Brickstone Square
Andover, MA 01810
508-470-1010
Fax: 508-475-6021
Use KM in subject field

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                  Conservation DistList Instance 8:69
                Distributed: Tuesday, February 28, 1995
                        Message Id: cdl-8-69-002
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