PMG Section 1.4.2 Standards, Guidelines, and Recommendations for Temperature and Humidity Levels During Exhibition

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Photographic Materials Conservation Catalog
Exhibition Guidelines for Photographic Materials

Date: July 2004
Contributors to WIKI version: Your name could be here!
Compiler: Stephanie Watkins, 1993-2004
Initiator: Douglas Severson, 1992-1993
Contributors (Alphabetical): Catherine Ackerman, Nancy Ash, Sarah Bertalan, Jean-Louis Bigourdan, Barbara N. Brown, Ed Buffaloe, Carol Crawford, Corinne Dune, Thomas M. Edmondson, Debra Evans, Julia Fenn, Betty Fiske, Gwenola Furic, Judy Greenfield, Doris Hamburg, Marc Harnly, Pamela Hatchfield, Cathy Henderson, Nancy Heugh, Ana Hofmann, Emily Klayman Jacobson, Martin Jürgens, Nora Kennedy, Daria Keynan, Lyn Koehnline, Barbara Lemmen, Holly Maxson, Constance McCabe, John McElhone, Cecile Mear, Jennifer Jae Mentzer, Jesse Munn, Rachel Mustalish, Douglas Nishimura, Leslie Paisley, Sylvie Pénichon, Hugh Phibbs, Dr. Boris Pretzel, Dr. Chandra Reedy, Nancy Reinhold, Andrew Robb, Grant Romer, Kimberly Schenck, Douglas Severson, Tracey Shields, Angela Thompson, Sarah Wagner, Clara von Waldthausen, Dr. Mike Ware, Stephanie Watkins, Dr. Paul Whitmore, Faith Zieske, Edward Zinn.

First edition copyright: 2004. The Photographic Materials Conservation Catalog is a publication of the Photographic Materials Group of the American Institute for Conservation of Historic and Artistic Works. The Photographic Materials Conservation Catalog is published as a convenience for the members of the Photographic Materials Group. Publication does not endorse nor recommend any treatments, methods, or techniques described herein.

Standards, Guidelines, and Recommendations for Temperature and Humidity Levels

History of standard

Many institutions have established internal guidelines and parameters for suitable environmental conditions during exhibition. There are no commonly agreed upon standards for temperature and relative humidity levels, however, research is ongoing. Organizations such as American National Standards Institute (ANSI) and International Organization for Standardization (ISO) have been steadily issuing standards for contemporary photographic materials. It is currently believed that fluctuations in relative humidity, rather than temperature, can be more damaging to many photographic materials. Deterioration rates based on the Arrhenius equation are often quoted (chemical deterioration doubles with every increase of 18°F [10°C]) in the literature.

Current guidelines and recommendations

General standards

• A temperature of 65°-75°F (18°-24°C) is recommended. "Daily cycling of more than 5-8°F (4-6°C) must be avoided" (Hendriks et al. 1991, 436). Some institutions have begun recommending even tighter restrictions of daily fluctuations under ± 3°F (2°C).
• A consistent 40-45% ± 3% relative humidity is recommended (Mathey et al. 1983). A consistent 30-50% relative humidity has also been recommended (Reilly 1986, 82).
• The National Information Standards Organization (NISO), Committee MM, worked during the 1990s on a draft of standards for exhibition of library and archives materials (239.79-1999) that included photographic materials. The NISO standards draft cited a temperature of 72°F (22°C) with a maximum variance range of 5°F (3°C) without shifting more than 5 degrees in any 24-hour period. This temperature was in conjunction with a general range of 30-50%, relative humidity allowing a seasonal drift of 5% over one month and no more than a 5% shift in any 24-hour period.
• Seasonal variances of highest and lowest acceptable range, or set points, can be set for environmental control systems to compensate somewhat for mechanical limitations of HVAC systems. Set points may also vary with region and location, such as coastal areas versus interior land locations, but they should aim as close to the guidelines as possible.
• It is advisable to maintain levels as consistently as possible. For the preservation of photographs, changes in humidity and temperature levels should be gradual.
• Please refer to the standards organizations section for contact information to obtain current standards.

Institutional guidelines and recommended standards
Temperature and humidity guidelines and standards established for institutions are often based on established standards set for paper items. Many institutions do not set a separate standard for photographic materials. Information listed here was gathered by an informal survey beginning in 1995 and augmented by compilers. It is provided as reference. Please consult individual institutions as necessary for current guidelines and recommended standards.

Institution (In house candle publication date, 1995 otherwise)	Temp °F	24 hour	Temp °C	24 hour	Relative Humidity %	24 hour fluctuation
National Gallery of Canada	Max 64-72°	+/-2°	Max 18-22°	+/- 2°	Winter 44%; Summer 50%	+/- 3% daily fluctuation
Museum of Fine Arts, Boston, MA (2000)	70°	---	21°	---	50% maximum	---
International Museum of Photography at the George Eastman House, NY	69-74°	+/- 3°	20.5-23°	+/- 3°	37-50%	+/- 5%
Philadelphia Museum of Art, PA	68-72°	---	20-22°	---	50%	+/- 5%
National Galley of Art, WDC (1998)	67-77°	+/-5°	19-25°	+/-5°	50%	+/-5%
Library of Congress, WDC (1998)	70°	---	21°	---	45-55%	---
Art Institute of Chicago, IL (ca 1990s)	68-70° during exhibit	---	20-21°	---	40% ideal	+/-5%
Art Institute of Chicago, IL (ca 1990s)	65-75° otherwise	---	18-24°	---	40% ideal; 35-55%	Without rapid change
Detroit Museum of Art, MI	68°	+/-2°	20°	+/-1°	45%	+/-5%
Cincinnati Museum of Art, OH (1996)	70°	---	21°	---	50%	---
Humanities Research Center at the University of Texas at Austin, TX (2004)	70°	+/-2°	21°	+/-1°	45%	+/-5%
J. Paul Getty Museum of Art, CA	67°	+/-3°	19°	+/-2°	45%	+/-5%
British Library, UK (ca 1990s)	Max 68°	---	Max 20°	---	30-40%	---
Victoria and Albert Museum, UK (1998)	68°	---	20°	18-25	50%	+/-5% max; range 45-60%
National Historic Trust, UK (1998)	Below 60°	---	Below 15.5°	---	45-55%	---
Bibliotheque Nationale, FR(1988)	60-68°	---	16-20°	---	50-60%	---

Recommendation by material
For cased materials, relative humidity levels no higher than 50% and possibly as low as 40-45% will reduce the potential for glass deterioration or condensation within the package, but will be high enough not to desiccate the leather, wood, textile, and paper components of the case and daguerreotype, ambrotype, or tintype package. Ambrotypes and tintypes commonly have at least one layer of a natural resin varnish. Therefore, heat and humidity probably pose the greater risk than does the actual level of illumination. However, light levels should not exceed 10-15 fc (107.6-161.4lx).

Regulating approaches to humidity and temperature

Heating, ventilation, and air conditioning (HVAC)
There are no standard heating, ventilation, and air conditioning (HVAC) systems applicable to all photographs in all exhibition or building situations. Specifications for HVAC systems are beyond the scope of this document. It is best to consult with a HVAC engineer to determine appropriate systems for each building, exhibition space, or exhibition case. Some general guidelines for operating HVAC systems follow:

• Perform regular maintenance of the HVAC system for optimum system efficiency.
• Perform regular filter changes to reduce likelihood of reemitting atmospheric contaminates and particulate matter if activated carbon / charcoal filters are used.
• Use close-range set points (e.g., 68-72°F or 20-23°C) for maintaining consistent environmental conditions. Allow for seasonal drift if determined necessary.

Enclosed microclimate
An enclosed microclimate within a case can be maintained at a predetermined humidity range with preconditioned amorphous silica (e.g., Silica Gel, ART-SORBTM, or ARTENTM) and housing materials that are naturally hygroscopic as appropriate to each situation (papers, boards, batting).

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