As with all archival material, the environment in which photographs and negatives are stored can go a long way in retarding deterioration. Maintaining stable temperature and relative humidity, as well as limiting exposure to light are crucial for long-term preservation.
Heat increases the rate of deterioration. Chemical deterioration of most photographic material is doubled with each 10°F increase in temperature. High relative humidity creates excess moisture which leads to chemical reactions that cause fading, discoloration, and silver mirroring. Excessively low relative humidity can lead to embrittlement and curling of photographs as well as flaking of glass plate emulsions. Fluctuations in temperature and relative humidity also cause damage such as cracking of emulsions or warping of photographic supports.
Temperature should be set between 65-68°F while relative humidity should remain between 40-50%, +/- 5%. Use of a monitoring device, such as the PEM2 (Preservation Environment Monitor) seen above, can provide accurate data which can be compared over time to ensure that the temperature and relative humidity meet and stay within desired levels.