I would be very interested in seeing the data related to the 5 degree
temperature data. Is it available anywhere for public consumption?
Thanks,
Sarah
Marc A Williams
<artconservation@CO To: [log in to unmask]
X.NET> cc: (bcc: Sarah M Allen/FOLA/NPS)
Sent by: Museum Subject: Re: [MUSEUM-L] Temperature
discussion list
<[log in to unmask]
.LSOFT.COM>
12/11/2008 08:32 PM
EST
Please respond to
Museum discussion
list
Charlie,
I just returned minutes ago from consulting on this very subject for a
group
of 6 museums in historic buildings. A lot of research has been done
recently on the effects of environmental fluctuations or changes on
historic
objects and materials. While it is a complex subject, several general
rules
apply, subject to specific exceptions.
1) Inorganic objects are less sensitive to environmental conditions than
organic objects. Therefore, control is based upon the more sensitive
organic objects which have the most restrictive needs.
2) Humans are sensitive to temperature. We can sense the difference
between
65 degrees and 70 degrees. However, we are not sensitive to RH variations,
and can't tell the difference between 45% RH and 50% RH. Organic objects
are sensitive to RH, and can "sense" the difference between relatively
small
RH changes. They are fairly insensitive to temperature differences. Thus,
needs of objects are almost always at conflict with needs of people in
historic buildings.
3) For collections preservation, RH should be controlled as a priority if
only one environmental variable (T and RH) can be safely controlled. For
historic structures, a range of 40%-60% RH is adequate. Tighter control
than this generally is not reasonable or possible. For this reason,
humidistatically-controlled heating (narrow RH range) is often used in
historic structures that contain collections, rather than controlling the
heat thermostatically (narrow T range).
4) Humidification of historic buildings generally is not recommended.
Doing
so in the winter can cause condensation in the walls and other areas that
can deteriorate the building fabric. Thus, it can be difficult, if not
impossible, to provide both steady RH and steady T during the heating
season.
5) A number of organizations/individuals have attempted to develop
deterioration calculations that will indicate the overall effect of the
various factors affecting preservation of collections. With respect to
temperature (temperature is energy, which accelerates deterioration
reactions), the best current metric indicates that for every 5 degrees
temperature DROP, the life of the object is DOUBLED. Thus, at 65 degrees,
the life is doubled over 70 degrees. At 60 degrees, it is doubled over 65
degrees or 4 times longer than at 70 degrees, and so forth.
6) For historic buildings, forget the standard of 70 degrees and 50% RH.
That was developed for purpose-built museums that had adequate insulation,
vapor barriers and other construction features that allowed maintenance of
these conditions. It also was heavily weighted toward human comfort. If
you are concerned with object preservation, significantly better
preservation would result with conditions of 40 degrees and 50% RH. If you
need to accommodate human needs, you will have to accept that sacrifices to
preservation need to be made by raising the T to human comfort levels, but
no higher than absolutely necessary.
Sorry for the primer, but to answer your specific question, if you lower
the
T to 68 or 66 or even lower, as long as you maintain 40%-60% RH, you will
NOT hurt your collections, but you will actually enhance their
preservation.
Marc
American Conservation Consortium, Ltd.
4 Rockville Road
Broad Brook, CT 06016
www.conservator.com <http://www.conservator.com/>
860-386-6058
*Collections Preservation Consultation
*Conservation Assessments & Surveys
*Environmental Monitoring & Low-Tech Control
*Moisture Management Solutions
*Collections in Historic Structures
*Collections Care Grant Preparation
*Conservation Treatment of:
Furniture
Painted Wood
Horse-Drawn Vehicles
Architectural Interiors
Marc A. Williams, President
MS in Art Conservation, Winterthur Museum Program
Former Chief Wooden Object Conservator, Smithsonian Institution
Fellow, American Institute for Conservation (AIC)
> -----Original Message-----
> From: Museum discussion list [mailto:[log in to unmask]]On
> Behalf Of Charlie Knight
> Sent: Thursday, December 11, 2008 10:18 AM
> To: [log in to unmask]
> Subject: [MUSEUM-L] Temperature
>
>
> I have a question regarding keeping a constant temperature/RH in
> exhibit areas. Our main museum is housed in a mid-19th century
> Court House (2 floors) and currently we keep the temperature
> between 68-72, usually right at 70, although some galleries run
> much higher temps than others. However, we have been instructed
> by our Dept Head (we are a City bureau) to reduce our energy
> consumption to cut our costs - obviously lights can be turned off
> when we're not open, but the temperature controls must remain on
> for the welfare of the artifacts on exhibit. So my question is
> would there be any harm in lowering our temperature by two (2)
> degrees, for a target range of 66-70?
>
> Charlie Knight
> MacArthur Memorial
>
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