Stable conditions are very important. Photographic materials are hygroscopic, readily absorbing and releasing moisture. They expand and contract with fluctuations in environmental conditions and these dimensional changes accelerate deterioration. Particulate matter and harmful chemicals in the air can damage photographs. Ideally air should be filtered for these materials, and dust should be kept to a minimum.
Light can cause embrittlement, yellowing, and fading in photographs.
Storage materials can be either paper or plastic. Both have advantages and disadvantages. Plastic enclosures that are acceptable include uncoated polyester, polyethylene, polypropylene and cellulose triacetate. These transparent materials allow the image to be viewed without the risk of being damaged by direct handling. Paper enclosures should be acid-free.