Relative humidity is the single most important factor in preserving most photographic materials. Low and fluctuating humidity may also damage them. High temperatures and high relative humidity levels will accelerate deterioration. Temperature, not relative humidity, is the controlling factor in the stability of contemporary color photographs. Appropriate enclosures for cold storage are available from various vendors.
Light can cause embrittlement, yellowing and color fading in prints and hand-colored surfaces.
Exposure of color slides to the light in the projector should be kept to a minimum. Use duplicate slides instead. Atmospheric pollutants, particularly sulfur compounds, will cause black and white images to fade and discolor. Gas by-products given off by fresh paint fumes, plywood, deteriorated cardboard and many cleaning supplies may cause accelerated image deterioration. Storage in non-acidic containers is recommended.