Saturated salt solutions to control humidity

Oliver Tietze <oliver.tietze [at] gmx__net> writes

>A small church near Leipzig has got an altarpiece from 1520. It is
>in very bad condition due to the rapidly changing climate during the
>service. In order to prevent more damage a showcase has to be built.
>The RH in the church in winter is around 60% and the temperature
>around 2 deg. C, rising up to 15 deg. C over 12 hours, and slowly
>decreasing over 2 day after the service and up to 22 deg. C in
>Summer.
>
>Now I am looking for a buffer material for the showcase. A saturated
>solution of calcium nitrate could be it. ...

I think a saturated salt solution is not an appropriate choice for
buffering a relatively short term RH excursion in a display case. If
the volume of the case is not large and the hygroscopic capacity of
the object is sufficient then no additional buffer would be needed.
If additional buffer is needed then it would be necessary to use a
larger surface area buffer such as paper, wood or a silica gel
impregnated sheet.  Saturated salt solution systems can have good
capacity for offsetting seasonal variations but pose challenges to
effective containment in permanent installations, are slow in
responding to RH changes and, hence, not appropriate for mitigating
RH excursions that last only hours or days.

Robert Waller, PhD, CAPC, FIIC
President and Senior Risk Analyst
Protect Heritage Corp.
622 Simoneau Way
Ottawa ON K4A 1P4
613-883-2707 (Canada)
303-872-9739 (USA)
Skype: rrwaller
and, Museum Associate Canadian Museum of Nature


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                  Conservation DistList Instance 25:15
                Distributed: Tuesday, September 20, 2011
                       Message Id: cdl-25-15-004
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