fairs to art dealers throughout the United States. Following the advent of Wash Art, many fairs developed throughout the United States. Preservation issues Although preservation issues are often disregarded in favor of other priorities during the exhibition process, they should certainly be considered so that possible damage to the collection is minimized or limited. As all objects in the library exhibition are unique and to some extent vulnerable, it is essential that they be displayed with care. Not all materials are able withstand the hardships of display, and therefore each piece needs to be assessed carefully to determine its ability to withstand the rigors of an exhibition. In particular, when exhibited items are archival artifacts or paper-based objects, preservation considerations need be emphasized because damage and change in such materials is cumulative and irreversible. Two trusted sources – the National Information Standard Organization's Environmental Conditions for Exhibiting Library and Archival Materials, and the British Library's Guidance for Exhibiting Library and Archive Materials – have established indispensable criteria to help curtail the deleterious effects of exhibitions on library and archival materials. These criteria may be divided into five main preservation categories: Environmental concerns of the exhibition space; Length of the exhibition; Individual cases; Display methods used on individual objects; and Security. Environmental concerns of the exhibition space The main concerns of exhibition environments include light, relative humidity, and temperature. Light Light wavelength, intensity, and duration contribute collectively to the rate of material degradation in exhibitions. The intensity of visible light in the display space should be low enough to avoid object deterioration, but bright enough for viewing. A patron's tolerance of low-level illumination can be aided by reducing ambient light levels to a level lower than that falling on the exhibit. Visible light levels should be maintained at between 50 lux and 100 lux depending on the light sensitivity of objects. An items level of toleration will depend on the inks or pigments being exposed and the duration of the exhibition time. A maximum exhibition length should initially be determined for each exhibited item based on its light sensitivity, anticipated light level, and its cumulative past and projected exhibition exposure. Light levels need to be measured when the exhibition is prepared. UV light meters will check radiation levels in an exhibit space, and data event loggers help determine visible light levels over an extended period of time. Blue wool standards cards