Glass negatives should be stored vertically (Clark 1990: 42), in four-flap negative enclosures to prevent peeling emulsions, and PAT-tested boxes to be labeled as heavy to prevent accidents (Wilson Part 1 1998: 4). Glass negatives can crack or break, but are otherwise well supported by the underlying material, which is not the case with the flexible film (Wilson Part 1 1998: 3).
Eastman Kodak first pioneered flexible, transparent film in 1889. Built on cellulose-nitrate, this film had a strong tendency to curl and was extremely flammable[**]. Scott Reid recommends copying these early cellulose-nitrate negatives onto safer film and destroying the originals in all cases where diplomatic analysis shows that it does not need to be kept for evidential purposes (Reid 1991), and Clark points out that if kept they should be removed to ventilated areas (1990: 42). Nitrate sheet film remained in use until about mid 1930s to early 1950s and was gradually replaced through the introduction of cellulose acetate in 1923, cellulose diacetate in 1937, and cellulose triacetate in 1947 (Messier 2005). Today, cellulose triacetate remains in use and was considered good archival quality until recent discoveries of instability (Messier 2005). Messier recommends films with a polyester base that were first introduced in 1955 (Messier 2005).
All cellulosic materials deteriorate through
similar mechanisms and preservation calls for sub-zero temperatures and
enclosures that pass photographic activity tests [††]:
"Environmental controls are essential for the preservation of film-based negatives. It is clear that typical ambient conditions (that is, approximately 40% RH and 70˚ F) are not adequate for the preservation of nitrate and acetate material. Of particular importance is the fact that once deterioration of a collection of negatives begins, it gains momentum rapidly, leading to the swift destruction of artifacts and increased health and safety risks." (Messier, 2005).
Stable negatives should be handled with lint-free cotton gloves, but deteriorated ones release harmful chemicals so should be handled with “neoprene gloves, goggles and a respirator” (Messier, 2005). Therefore, deteriorating negatives can be recognized by the smell, and should be immediately and continually segregated from the stable ones to prevent the acceleration of deterioration (Wilson Part 1 1998: 6). Transparencies (e.g.: 35mm slides), should be stored in polypropylene, polyethylene or polyester sleeves or carousel trays (Wilson Part 1 1998: 6).
[**] a fire in 1909 at the Fergusin Film Exchange Building in Pittsburgh prompted the National Board of Fire Underwriters to draw up regulations regarding the handling and storage of nitrate film (Messier, 2005)
[††] specified in ANSI Standard IT 9.2-1991