<P> The exhibition space's relative humidity (RH) should be set to a value between 35% and 50% . The maximum acceptable variation should be 5% on either side of this range . Seasonal changes of 5% are also allowed . The control of relative humidity is especially critical for vellum and parchment materials, which are extremely sensitive to changes in relative humidity and may contract violently and unevenly if displayed in too dry an environment . </P> <Dl> <Dt> Temperature </Dt> </Dl> <P> For preservation purposes, cooler temperatures are always recommended . The temperature of the display space should not exceed 72 ° F. A lower temperature of down to 50 ° F can be considered safe for a majority of objects . The maximum acceptable variation in this range is 5 ° F, meaning that the 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 can be maintained as well . Controlling the environment with 24 - hour air conditioning and dehumidification is the most effective way of protecting an exhibition from serious fluctuations . </P> <P> One factor that influences how well materials will fare in an exhibition is the length of the show . The longer an item is exposed to harmful environmental conditions, the more likely that it will experience deterioration . Many museums and libraries have permanent exhibitions, and installed exhibitions have the potential to be on the view without any changes for years . </P>

Who determines what and when artworks are exhibited