Exhibitions, whether of general or specialist interest; local, regional or national significance, are conceived with three fundamental principles in mind: to inform and to entertain visitors and to increase interest in museums among the public. While we may praise or condemn the finished product - its appearance, composition, the choice of artefacts and even the intent of the subject-matter - we often forget that these artefacts have only been assembled for the duration of the exhibition, which may last from a few weeks to a number of years. They existed before the idea of the exhibition was conceived, and, with care, should continue to exist after the exhibition has closed and all the objects have been dispersed.
This is not the place to discuss the legal and contractual complexities of exhibition organisation. It is, however, appropriate to consider in a little more detail whether exhibitions provide a safe environment for artefacts, what the conservation risks are and how, with planning, these risks can be minimised. Safety is a word well understood and legislated for in the context of human life, but what does a safe environment for artefacts mean? What are the key conservation issues in exhibition design?
Paradoxically, while audiences give life to an exhibition, the very presence of visitors can threaten artefacts. A sudden and violent attack to destroy, vandalise or steal an object is as shocking as it is dramatic. But what is often unrecognised or forgotten is the slow and insidious damage caused by crowds breathing over artefacts, causing ambient humidity and temperature to rise, and the even less well-known effect of perfumes, sprays and lotions evaporating into the air as complex pollutant gases. Such effects can be designed out of an exhibition with a well-regulated environment and with good space planning which enhances visitor flow and avoids bottlenecks.
The designer of an exhibition with conservation in mind must consider, at the earliest opportunity, the management and use of the space for the duration of the exhibition. It is very rare these days for an exhibition not to have attendant activities, whether they are educational programmes or private functions. The number of occupants and the frequency and nature of these events will need to be taken on board when designing the layout and the environmental control of the space.
What must be avoided at all costs is designing for the exceptions, such as one-off private views, as this only leads to unnecessary over-specification and expense. The one exception to this rule is the care given to the provision of food and drink during private functions and the use of living plants and flowers to decorate an exhibition. All these increase the threat of pest infestation to organic materials, such as wood, paper, textiles and leather.
So what part do the exhibition designer and contractor play in delivering an exciting exhibition which minimises the risk to artefacts? A few basic guidelines can help negotiate the more obvious conservation pitfalls.
Consider the areas around the exhibition venue as well as the space itself
Good physical access to the space for the artefacts is essential, as is weather cover for any transport vehicles. For environmental and security reasons, the unloading point into the space should not open directly onto the street.
Think whether the artefacts will be unpacked in the exhibition space: how will this affect the construction programme? Will it create additional and unnecessary dust?
Where will wrapping materials and packing crates be stored? Ideally they should be kept in conditions not dissimilar to the environmental conditions in the exhibition space.
Consider carefully the selection of objects for display.
Sometimes the fragility of an artefact requires a difficult decision over whether or not it should be displayed at all. A conservator should review the list of artefacts to be displayed in relation to the proposed exhibition design.
The question of whether or not artefacts should be exhibited outside cases is often controversial. While many materials can be placed on open display without serious adverse environmental effects, some classes of materials such as paper and textiles, and artefacts with friable surfaces, should be separated physically from the environment around them. Display cases can provide both environmental and security protection.
The standard conservation requirement that objects on display should not be touched or handled can make the experience of an exhibition less rewarding for some visitors. Conservation condition reports on the artefacts, often prepared prior to the exhibition, should include an assessment of whether the objects can be touched or handled. Among the assessment criteria are the international, national, regional or local significance of the artefacts, their rarity and their vulnerability to damage. As a general rule, objects which are central to the museum's collections may not be touched, while duplicates, which often form part of a handling collection, are used for demonstrations.
Carefully consider the selection of construction materials, internal display finishes and any other materials than will come into contact with artefacts
Corrosion damage can occur to materials such as silver, lead and copper when chemically unstable construction and display materials are used. Allow at least six weeks in the construction programme for testing all materials for safe use with objects. As it is likely that some materials will fail the test, it is wise to test a selection of materials.
Be aware that surface sealing of poor-quality materials to prevent the emission of corrosive vapours may not be enough to stop damage to artefacts, particularly if the exhibition is expected to run for longer than six months.
Display cases must be selected carefully. Decide whether the artefacts will be safer in vented or sealed cases. It is important to use the tracer- gas technique to measure the air-leakage rate of the cases, particularly if microclimates are being considered.
Assess the buildability and maintainability of the exhibition installation before the design is finalised
The exhibition design should have simple lines, and special attention should be given to detailing during construction to make it easier to clean the space. Avoid dead spaces as they can become breeding sites for pests. Good design should go hand-in-hand with pest management and control.
Avoid designs that will require artefacts to be moved from their display location during the exhibition for routine maintenance to services or lighting systems.
If the time between the completion of the construction programme and the opening of the exhibition is tight, reduce the amount of 'wet work' as there will be little time to dry out the space before artefacts are put on display.
Discuss with a conservator the mounting and hanging methods of objects proposed by the designer. Avoid using temporary or permanent adhesives applied directly to artefacts. Display methods which put any undue strain on any part of an object must also be avoided.
Not everyone can visualise a three-dimensional design when drawn on paper. When a permanent or important temporary exhibition is being planned, use a model to help everyone involved understand the design and to enable them to suggest improvements to the conservation of the artefacts.
Decide on the environmental strategy for the exhibition
Most artefacts will withstand broad-band control of ambient relative humidity and temperature. Those which cannot may be protected by microclimates within display cases. Depending on the air tightness of the cases, climate control can be achieved either by using the display-case enclosure on its own to mitigate environmental fluctuations, by using a hygroscopic buffer material to assist in stabilising conditions within the case, or by mechanical control of the case.
Depending on the objects' vulnerability to light, the design may combine daylighting and electric lighting. All light sources should preferably be external to the display case and all ultraviolet radiation must be eliminated, whatever the source. Take every opportunity to reduce light intensity and strike a balance between visual acuity and conservation of the artefacts. For energy efficiency reasons the lighting load should be no greater than 15-20 watts per m2.
Ventilation is primarily to satisfy human comfort, though there is some reason to believe that concentrations of internally generated pollutants are diluted by increasing the ventilation rate. The disadvantage of mechanical ventilation is that often larger volumes of air than are necessary are moved around the space. Depending on the building location, control of external pollution may be necessary. It is relatively inexpensive to control; but a decision to control gaseous pollution should be based on local pollution data.
The design of the exhibition must allow for the monitoring of environmental parameters which present most risk to the artefacts on display - light, relative humidity, temperature, pollution and pests.
None of this advice allows for the fact that artefacts may need conservation or restoration prior to display. This may involve complete dismantling and reconstruction. Such procedures take time and cannot be rushed. This means that last-minute changes to lists of exhibits may compromise the conservation of the artefacts on display. The message is that the conservation and environmental needs of artefacts must be built into the exhibition programme from the start.
May Cassar is environmental advisor at the Museums & Galleries Commission