CONSERVATION POLICY AND THE EXHIBITION OF MUSEUM COLLECTIONS
3 ENVIRONMENT PLANNING AND CONSERVATION
Environmental factors have been referred to in the previous section, but will be elaborated upon in relationship to museum buildings, and their component parts. It is perhaps redundant to emphasize that the condition of an object is the result of the sum total of all its exposures to deterioration factors: during storage, conservation treatment, exhibition, and movement (travel). The housing of collections has therefore an important bearing on conservation. Museum architecture is a rather specialized field that does not have a long enough history or experience to offer guidelines and specifications for conservation. While progress has been made in developing newer approaches to exhibition halls, lighting and storage; humidity control, air movement, and filtration still pose great difficulties for the architect and the mechanical engineer. The conversion of older structures for museum use is a complex matter; likewise is the upgrading of the physical environment of museums built years ago. The concept of collaboration between architect and conservation specialist is rather recent. This new approach was incorporated in a number of the conclusions reached at the ICOM-UNESCO Symposium on Museum Architecture, Access, and Circulation, Mexico City 1968.19 Relevant conclusions are extracted:
- Museums are one of the major cultural and scientific institutions serving human society.
- The basic purpose of a museum is to enable the public to know and appreciate, under the best conditions of display, the objects and other items the institution is asked to collect, study, conserve and protect.
- The architect should:
participate in an advisory capacity in the preparation of the museum program and in the work of a team composed of all the necessary specialists, particularly in the fields of museography, conservation, and psychosociology;cooperate closely with the director of the museum during the entire period of planning the architectural design.
- Conservation, one of the essential tasks of a museum, implies that measures are taken, from very beginning of the construction and equipping of the building, to prevent any deterioration due to insufficient, excessive or variable humidity, to avoid pollution of the atmosphere by dust or gases, to ultraviolet rays or to visible light.
- It is therefore essential that the plans for new museums and any alterations made in old buildings in order to convert them into modern museums should regularly include such installations and equipment as will ensure conservation under good conditions.
- It is therefore recommended that one or more specialists in conservation should be associated in the preparation of the museum program, in the establishment of the building plan and in the various stages of construction.
In some institutions surveys are conducted of museum buildings to establish their conservation-worthiness. Such surveys tend to be detailed, including records of humidity and temperature, and light intensity readings. The American Association of Museums embarked on a Museum Certification Program, a number of years ago, in which among a number of factors, environmental stability is assessed. In Canada, the National Gallery, many years ago, categorized art museums A, B, C, or D in descending order of professional and technical excellence. Building and environmental surveys are not only very important to the occupants and the collections housed, but also to other institutions who wish to lend or borrow objects. An inventory of building survey reports, including reliable historical data on relative humidity, temperature, air quality, and light levels would be very valuable to conservators and exhibition organizers. The weak point is the reliability of the instruments used in surveys, and the selection of locations for measurement of the various factors.
The matter of level of relative humidity to be maintained for collections is still unsettled. It is generally agreed upon that constancy with narrow variation is essential for maintaining dimensional, or geometric stability for hygroscopic objects. It is also accepted that the temperature factor is less critical in these considerations. In 1960, ICOM carried out an international survey7 on desirable norms for relative humidity and temperatures. The answers were forthcoming from 3 archival institutions in Europe, and 29 major museums and galleries in Europe and America. The desirable levels varied considerably from highs of 60–70% to 45–50% for relative humidity, and from 15–22° C for temperatures. Obviously, there should be another survey, more detailed in nature, covering many more institutions and, this time, segregating the norms for classes of objects; e.g., paintings, works on paper, archival objects, sculptures (hygroscopic or otherwise), textiles, leather, ethnographic objects, ceramics and metals. Permissible variations should also be included, along with external climatic data for each reporting institution.
In the author's experience with Canadian museums,20 there has been flexibility in the control levels over a twelve-month period to take into account the preservation of the building in a difficult climate. Thus in the winter time, the relative humidity can be set at 40 ± 5%, and permitted to rise to 50 ± 5% in the summer. The temperatures can likewise be programmed from 18° C in the winter time to a high of 24° C in the summer, as shown in Figure 3. The lower wintertime levels resolve to some extent the condensation problem in buildings and energy costs. If certain objects in the collection require very stringent controls then they can be kept in specially designed cases at specific humidity levels. This is a more realistic solution to environmental control than that of arbitrarily imposing throughout the building a uniform high relative humidity level, which is also very costly to maintain. It should also be realized that owing to air movements in buildings and the nature of wall materials there will be local variations in climate even within controlled buildings. Measurements taken near exterior walls can be quite different from those taken in the center of a gallery. In some older museums, it is best not to install overall humidity control, relying instead on display cases and storage cabinets. This was the decision made by a large natural history museum. Simple encasing of a hygroscopic object can under certain conditions offer stability, the cheapest solution of all. There is the problem, too, of how to deal with composite objects; e.g. made of wood and metal.
As regards lighting not much has been written on the conservation side since 1964.8 Generally, works on paper and textiles are being displayed at recommended low levels of ultraviolet-free light, 150 lux and lower, the fluorescent lamps and daylight sources protected with ultraviolet absorbing filters. There appears to be however a return of natural lighting to museums, partly as a reaction to the “dead” and unchanging aspect of artificial light. A compromise solution to this can be the location of windows or skylights remotely from the works of art, offering a psychological relief to the viewer. Architects find this solution attractive.
The remaining factor of dust and dirt control can be resolved with filtration systems designed to eliminate dust and dirt particles down to certain levels (e.g. below 1 micron diameter). Atmospheric pollutants, e.g. sulfur dioxide, can be largely removed in filtration/wash system. However, in an industrial environment such pollutants can gain access through doors, windows, etc., and affect works of art. Thus careful attention must be given to the design of all building openings.