By Colin Pearson
For museum collections, the best environment is a stable one. Among other things, that means an environment where there are only moderate changes in temperature and relative humidity. Extreme fluctuations of either can cause significant stress in objects, and the results can be destructive. Paint can crack on a canvas or pop off a painted object, wooden veneers can peel away, glued joints on wooden furniture can fail, and wooden objects can be permanently deformed.
In industrialized countries, most large museums provide stable environments for their collections by using elaborate air-conditioning systems that operate 24 hours a day. However, at the many more small museums—particularly those in tropical countries—there is not the money to install, run, and maintain sophisticated climate-control systems. Because of a lack of understanding of climate control for museums, some at these institutions believe that unless they can match the environments of air-conditioned museums, their collections will rapidly disintegrate.
In fact, air-conditioning systems themselves can create problems. If a system is designed primarily for human comfort and controls temperature alone, or if it is inefficient or improperly maintained, it can actually cause more damage to the collections than if there were no air-conditioning at all. For example, museum buildings that are designed to be air-conditioned often provide little climate control for the collections when the air-conditioning breaks down. The shutting off of a system (either when it is turned off at night to save money or when it breaks down) can cause significant temperature and humidity fluctuations.
For instance, a museum in Thailand has two of its galleries air-conditioned, but for only seven hours each day; on weekends and public holidays, the air-conditioning is switched off. These galleries experience greater fluctuations in temperature and relative humidity than do the museum's non-air-conditioned galleries, with the end result being that the collections in the former galleries will deteriorate faster. (Similar fluctuations are created by switching spotlights on and off, or by allowing direct sunlight to fall on artwork.) The optimal environment for museum collections is one that is not only cool, but also stable.
The hotter the temperature and the higher the humidity, the faster the deterioration of materials. Collections do best when the level of relative humidity is between about 40 and 70 percent. Below 40 percent, many materials dry out; above 70 percent, mold and bacteria can grow. For museums in dry or humid tropical countries, these conditions are difficult to meet. The temperatures are rarely below 20°c and are often around 40°c, and the relative humidity is often either up to 95 percent or down to 10 percent.
How can safe environments be provided to ensure the long-term preservation of museum collections in tropical countries? The answer lies in the use of passive environmental controls, relatively inexpensive and simple methods for creating reasonably stable museum environments by reducing extreme conditions. This is the approach being promoted by the Getty Conservation Institute (GCI) and the University of Canberra, Australia. With this approach, airconditioning is not even considered, apart from such basic features as a portable dehumidifier if the relative humidity is very high, along with air-circulating fans to help prevent mold growth.
A current project is a review of the literature on environmental management for cultural institutions in tropical countries. The literature review is being developed in part as the result of a workshop on the subject held at the GCI in 1992. At the workshop, the level of current knowledge was discussed, with gaps identified by experts in related fields. The information that exists is focused primarily on human comfort and is therefore not completely applicable to museum collections. Human beings are far more adaptable to environmental changes than are museum objects. In hot, dry climates, people stay inside buildings during the day and sleep outside on roofs at night. If they get too hot, they can remove clothes; if they get too cold, they can put clothes on. People can also tolerate fluctuations in relative humidity. Objects in museum collections lack this flexibility and cannot simply be moved around or covered up as environmental conditions change.
There is a need to raise awareness of the damage that can be caused to museum collections by adverse conditions and to suggest simple approaches for creating a stable and safe environment. For example, inside one museum in Vietnam the relative humidity was measured at 90 percent—higher than the level of 80 percent outside. The reason for this was that the floors were mopped twice a day. Reducing the relative humidity inside the building involved the simple step of altering this long-standing custom.
In another museum in Vietnam, all the furnishings and display cases were covered with condensation. The reason? The museum was tightly closed, and the air-circulation fans were not in operation. The prescription for providing a stable environment in this museum included switching on the fans and opening the doors and windows when the external environment was at an acceptable level. When it was not, the museum could be sealed as tightly as possible, with the fans operated to circulate air. At the same museum, incandescent spotlights were located inside a display case just a few centimeters away from an organic object, causing heat and light damage. In addition, there were rapid changes in relative humidity when the lights were switched on and off. The simple solution was to move the spotlight out of the case and install it at a safe distance from the object.
The use of natural and forced ventilation to provide a more stable environment for museums in hot, humid climates is common practice. However, this approach can mean that air pollutants are brought into the building. Many urban centers in newly industrializing countries have serious pollution problems. The challenge for museums is to find a cheap and efficient method of removing air pollutants from the atmosphere. Display cases and storage units constructed with special materials can provide some level of pollution control, but more research in this field is required.
The literature review mentioned earlier, which is being prepared by this author with support from the GCI, will discuss the problems of temperature, relative humidity, light, air pollution, and pests in tropical countries, and the traditional methods of controlling these. In addition, this author is developing a manual that will detail recommended environmental standards and propose passive techniques. It will cover the museum building site, building location and orientation, landscaping, building design and construction materials, and control of the climate, air pollution, and pests in the museum buildings, display cases, and storerooms. Advice will also be provided on how to determine the major threats facing a museum and its collections.
The GCI is also investigating the environmental problems associated with collections in hot and humid environments. The objective of its project is to identify practical strategies for reducing environmentally caused deterioration of museum objects. Strategies for managing the museum environment—from the building itself to display cases within the building—will be studied. In pursuing this project, the Institute will be working with this author and other individuals and organizations with extensive experience in dealing with the environmental problems of collections in hot, humid climates. The GCI will be sharing the information it acquires and disseminating the results of its work.
An important portion of the world's cultural heritage resides in tropical countries where both the human and financial resources for preserving museum collections are limited. However, it is already clear that there are steps cultural institutions in these countries can take to provide a more stable environment for their collections. It is hoped that the information now being developed will offer even more tools to these institutions to aid them in preserving the objects in their keeping.
Colin Pearson is the director of the National Centre for Cultural Heritage Science Studies and a professor on the Faculty of Applied Science at the University of Canberra, Australia.