Sarah,
Earlier this week, I read over a lot of information from a number of on-line
sources. I can't recall exactly where this approximation came from, but an
alternate resource is the Preservation Calculator from the Image Permanence
Institute of the Rochester Institute of Technology. Based upon it, at
constant RH, a temperature drop of 9-10 degrees doubles the life of the
object. 70 degrees and 50% RH has a preservation index of 39 years. 40
degrees and 50% RH has a preservation index of 333 years, or more than an
8-times greater lifespan. All of these metrics are theoretical and can not
possibly include all of the variables in the environment of an object.
However, all of them agree that lower temperatures increase 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 Sarah M. Allen Sarah Allen Museum Technician Knife River
> Indian Villages NHS Stanton, ND 58571-0009 701.745.3300
> Sent: Friday, December 12, 2008 1:29 PM
> To: [log in to unmask]
> Subject: Re: [MUSEUM-L] Temperature
>
>
> 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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