Linda,
First, I will state that while many museums believe in climate control,
many are not able to accomplish it. Many museums are in old buildings and
it would be expensive to retrofit them with the appropriate climate
control systems. At the Carnegie Museum, the Section of Mollusks was
air-conditioned for the first time last year. We still do not have a
system that maintains strict control of humidity. However, a study of
humidity within our cabinets shows reasonably stable levels of relative
humidity so it may not be important to retrofit the whole room for control
of humidity.

Universal recommendations are difficult to come by. For a collection of a
given type of specimens and storage conditions, you may find several
different recommendations of temperature and humidity to aim for. Shales,
clays, and amber can crack and flake if the humidity gets too low. Some
shells, such as the gastropod genus Paryphanta and the bivalve genus
Pyganodon will get too dry at low humidity and crack or shatter. At low
humidity levels paper can get brittle. What we need to strive for is a
good compromise between the needs of the collection and a reasonable
working environment for people In general, if the relative humidity of a
shell collection is maintained within the range of 50-55%, one should not
be concerned. This, with a temperature range of 16-21degrees Celsius
(60-70 degrees Fahrenheit) is well within the abilities of most home
heating/ventilation/air conditioning systems and may only need occasional
help from a dehumidifier. The best way to monitor the RH is with a wet-dry
bulb thermometer or a hygrometer.

My collection is in a small room in my basement. The temperature year
round ranges from a low of 60 degrees Fahrenheit in the winter to a high
of about 68 in the summer. The relative humidity is relatively constant in
the winter (about 50-55%) while in the summer it can range up to 65 %. I
use a dehumidifier to keep the relative humidity between 50-60 %; I try to
stay around 50-55%. I use a mechanical Abbeon Model HTAB 169B
hygrometer/thermometer combination to measure the temperature and relative
humidity. The dehumidifier does not keep very tight control; I adjust it
before leaving for work in the morning, my wife checks it mid-day and I
check it again in the evening.

Hope this helps.

Regards,
Charlie
******************************************************************************
Charlie Sturm, Jr
Research Associate - Section of Mollusks
                     Carnegie Museum of Natural History
                     Pittsburgh, PA, USA

Assistant Professor - Family Medicine

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