Such expositions may present pictures, drawings, video, sound, installation, performance, interactive art or sculptures by individual artists, groups of artists or collections of a specific form of art. The art works may be presented in museums, art halls, art clubs or private art galleries, or at some place the principal business of which is not the display or sale of art, such as a coffeehouse. An important distinction is noted between those exhibits where some or all of the works are for sale, normally in private art galleries, and those where they are not. Sometimes the event is organized on a specific occasion, like a birthday, anniversary or commemoration.
Preservation issues, though often disregarded due to other priorities, should be considered during exhibitions, so that possible damage to the collection could be minimize or limited. As all objects on the exhibition are unique, rare, and valuable, it is essential to care objects without any damage. When exhibited objects are especially archival artifacts or paper-based ones, preservation considerations would be more emphasized because damage and change in paper-based objects are cumulative and irreversible. A standard, American National Standard Z39.79-2001, Environmental Conditions for Exhibiting Library and Archival Materials, establishes criteria to minimize the effect of environmental factors on deterioration of library and archival materials on the exhibition. There are four main categories to be considered on preservation issues during the exhibition: Environmental concerns of the exhibition space; Length of the exhibition; Individual cases; and Display methods used on individual objects.
The intensity of visible light should be low not to deteriorate objects, but it needs to be bright enough for viewing. Visible light levels are set at between 50 lux and 100 lux depending on the light sensitivity of objects. Light levels shall be measured when the light is set for the exhibition. Invisible radiation, such as UV, should be prevented from falling on the exhibited objects. It is recommended that UV light should be limited no more than 75 microwatts per lumen at 10 to 100 lux. Only artificial light sources are recommended for the exhibition. Exposure to natural light is undesirable because of its intensity and high UV content. When exposure to natural light is inevitable, any measures to control UV, including using UV-filtering films or UV-filtering panels in windows or cases, are required. Among artificial light sources, incandescent lamps are most suitable for the exhibition because they give off little or no UV. Fluorescent lamps, common in most institutions, are unsuitable for the exhibition since they can not be dimmed and they emit UV. Even though tungsten-halogen lamps are currently one of favorite artificial lighting sources and can be dimmed, yet, they still give off significant amounts of UV. Lights should be turned off when visitors are not in the space.
The relative humidity (RH) should be set between 35% and 50%, inclusive. The maximum acceptable variation should be 5% on either side of the set point. Seasonal changes of 5% are also allowed. The control of relative humidity is especially critical for objects on vellum and on wood, which are extremely sensitive to changes in relative humidity.
For preservation purposes, cooler temperatures are recommended, but the temperature of the exhibition should be set not to exceed 72°F. A lower temperature, down to 50°F, should be considered safe for majority of objects. The maximum acceptable temperature variation is 5°F, which means that temperature should not go above 77°F and below 45°F. As temperature and relative humidity are interdependent, temperature should be reasonably constant so that relative humidity could be maintained as well. Controlling the environment with 24-hour art conditioning and dehumidification would be the most effective way of protecting an exhibition.
Unbound materials, usually single-sheet items, unless matted or encapsulated, need to be attached securely to the mounts. It is recommended to use photo corners or polyethylene or polyester film straps to hold the object to the support. Objects may also be encapsulated in polyester film. However, research at the Library of Congress reveals that acidic papers deteriorate rapidly within polyester envelopes. Thus, old and untreated acidic papers should be professionally deacidified before encapsulation. Encapsulation should be carefully done because of potential slippage. When possible, encapsulation should be done with ultrasonic or heat seals. When objects need to be hung, which may require more protection than lightweight polyester film, matting would be an effective alternative. Matting, consisting of two pH-neutral or alkaline boards with a window cut in the top board which enables the object to be seen, does not offer more protection than framing. Objects in frames should be separated from harmful materials through matting, glazing, and backing layers. Objects should be matted before framing so that glazing should not come in direct contact with the object. Backing layers of archival cardboard should be thick enough to protect objects. Frames should be well sealed and hung securely, allowing a space for air circulation between the frame and the wall.
The most common way to display bound materials is closed and lying horizontally. If a volume is shown open, the object should be open only as much as its binding allows. Common practice is to open volumes no greater than 135 degrees. There are some equipments supporting volumes to be displayed open: blocks or wedges, holding a book cover to reduce stain at the book hinge; cradles, supporting bound volumes to be open without stress to the binding structure; polyester film strips, helping leaves to be open secured. It is recommended to turn the pages every few days in order to protect the page from exposure to light. It should be remembered that keeping a book open for long periods can damage its structure.