How should I store negatives and transparencies?
Negatives and transparencies can be stored the same way as photographic prints, using the same high quality papers and plastic which pass the ANSI IT9.16 Photographic Activity Test (PAT). (The PAT was developed by the American National Standards Institute (ANSI) and is a test that determines whether or not a storage material will cause fading or staining in photographs.) There are paper and plastic enclosures and storage boxes designed for film formats available from most manufacturers. Like prints, negatives and transparencies should be stored in a cool, dry location.
Fortunately, many negatives now return from the photo lab stored in plastic pocket pages that appear to be safe for the films (they frequently are polyethylene). Likewise, the plastic boxes that store slides are usually safe (they frequently are polypropylene). Slides can also be stored in plastic slide pages (a type of pocket page which holds 20 slides) or stored in metal or cardboard slide boxes.
Older plastic or paper enclosures which came from the photo lab may not be safe for long term storage of photographs. If the paper has become brittle, has stained or marred the photo, or has caused fading, it should be replaced with a high quality envelope which passes the PAT.
Old film negatives may develop a vinegar odor with time, or warp and wrinkle. This is a sign that the plastic is deteriorating. Only storage at cold temperatures can slow this irreversible decay process. Cold storage is not practical for most people and can even cause more immediate damage if used improperly. However, frost-free freezers can be used as long as special enclosures and handling procedures are followed (see Cold Storage Handling Guidelines for Photographs). If the negative is very important and needs to be kept, it should be duplicated. (See: Where can I find sources for duplicating/copying historical photographs?)