A PRACTICAL APPROACH TO ENVIRONMENTAL REQUIREMENTS FOR COLLECTIONS IN HISTORIC BUILDINGS
RICHARD L. KERSCHNER
2 EVALUATION OF THE COLLECTION
Controlling environmental conditions within museums has positive effects on the preservation of artifacts that have been recognized for decades. In general, fine arts museums led the way during the 1960s and 1970s, installing climate control systems designed to maintain ideal conditions of 65°F to 70°F and 50% ± 3% RH. In 1984, the Institute of Museum Services, a major U.S. governmental granting agency for conservation, placed environmental control above artifact treatment in its funding priorities. As a result of this increased emphasis on environmental control, many museums that had not yet addressed environmental conditions sought guidance on environmental improvements. Conservators and preservationists working with museums housed in historic buildings, especially those in cold climates, realized that ideal environmental conditions for the preservation of the artifacts housed in the buildings were not the same as the ideal conditions for the preservation of the buildings. Sepcifically, maintenance of an interior relative humidity of 50% during the cold winter season could result in moisture condensation within the wall cavities, causing serious damage to the building structure. A reasonable compromise of environmental standards was required to maximize preservation of both artifacts and buildings.
While most artifacts require some degree of climate control, many historic and fine art collections artifacts can safely survive under a range of environmental conditions considerably wider than 50 ± 3%RH. As early as 1964, Richard Buck proposed a median RH level of 55%, varying from 45% in winter to 65% in summer (Buck, 1964). In 1971, George Rogers of the Canadian Conservation Institute also proposed the adoption of a range of safe RH levels (Rogers, 1976). In 1980, Ralph Eames offered the following advice in a presentation at the International Institute for Conservation Vienna Congress:
It is now generally acknowledged that to demand an unvarying temperature of 20°C and relative humidity level of 55% can be counter-productive since these constant levels are almost impossible to maintain in Canada. (Counterproductive because the on-site manager, whatever his title, throws up his hands in despair and does nothing. Furthermore, any advice subsequently given will be received with scepticism.) It would be far better to advocate what could be physically and financially achieved, i.e. an annual range of temperature between 7°C in winter and 26°C in summer and relative humidity between 35% and 60%, with changes being retarded as much as possible (Eames 1980).
Canadian conservators and scientists were implementing a more flexible approach to environmental standards as early as 1979, when the Royal Ontario Museum (ROM) published In Search of a Black Box(ROM 1979). This publication summarizes an evaluation of ROM's collection artifacts by type to determine humidity and temperature ranges, and light levels that would be safe for the artifacts and the building. The goal of the study was to determine which artifacts could be safely displayed in which parts of the building, since a new addition with different environmental capabilities was being added to an existing structure. During this project, five categories of sensitivity were established for the collection artifacts (ROM 1979). Environmental conditions and major artifact types that were assigned to each category are presented, slightly edited, in table 1. Although proposed 15 years ago, these guidelines are still applicable today with one possible exception: Paintings on canvas that are not backed and glazed should probably be placed in Group 3 “Requir Extremely Stable Conditions”, instead of Group 2 (Michalski 1990). Following the guidance of the ROM, many artifacts of the type that are usually found in historic house museums are safe under “stable ” conditions, i.e., 35%–50% RH.
TABLE 1 CATEGORIES OF SENSITIVITY
For general collections housed in historic buildings in the northeastern United States, I endorse Ralph Eames's suggested relative humidity range of 35% to 60% with gradual seasonal changes. Environmental control to these realistically attainable conditions will be easier to maintain and safe for the majority of collection artifacts and historic building structures. Sensitive artifacts that do require narrower ranges of relative humidity should be displayed in macroclimates maintained in portions of the building that can support more stringent conditions, such as an interior room where higher RH levels will not cause moisture to condense in cold outer wall cavities. Artifacts that are extremely sensitive to RH fluctuations, such as oriental lacquer or paintings on canvas that are not glazed and backed, may have to be displayed in buffered or climate controlled cases, since it is not practical to attempt to control the entire building to such stringent requirements for just a few artifacts.