What effect can the environment have on a photographic collection?
Various aspects of the environment, such as relative humidity, temperature, air purity, and light, influence the stability of a photograph collection.
Relative humidity is the single most important factor in preserving photographs from chemical deterioration. High relative humidity speeds detrimental chemical reactions, leading to much of the fading and discoloration visible in photograph collections. Relative humidity should be kept below 50%; ideally it should be 35%. Stable conditions are very important.
Temperature control is important mostly because of its influence on relative humidity. High temperatures will speed up chemical deterioration. The recommended compromise temperature for the storage of photographs and the comfort of people is 68 degrees F. Lower temperatures are desirable, especially for color materials. Sharp fluctuations in relative humidity and temperatures should be avoided. By using folders and boxes, the effect of environmental fluctuations on the photographs can be minimized. The use of dehumidifiers and humidifiers can also be helpful. Avoid attics (too hot) or basements (too damp) for storage areas. Storage in an interior closet would be much better. Do not hang or store photographs on exterior walls, in bathrooms, or over heat sources.
Air purity is particularly crucial in a city environment. Harmful chemicals as well as particulate matter can damage photographs. Ideally, air should be filtered for these materials and dust should be kept to a minimum.
Metal cabinets are preferred over wood because wood generates harmful gases. If wood is used, it should be sealed with polyurethane or water-based acrylic paint. Keep photographs away from fresh paint fumes, plywood, cardboard, and janitorial supplies. Light can cause embrittlement, yellowing, and fading in photographs. Direct sunlight is the most harmful; incandescent (tungsten) lighting is preferred to fluorescent. Avoid hanging photographs where they will be exposed to direct sunlight or to fluorescent lights. Ultraviolet-filtering Plexiglas is recommended for use in framing any photograph which is on long-term display.