Journal of Film Preservation - FIAF

Biodegradation of Motion Picture Film
Stocks
Concepción Abrusci, Norman S. Allen, Alfonso Del Amo, Michelle Edge, Ana Martín-González
Technical
Column
Chronique
technique
Columna
técnica
Introduction
In recent years, the concern about the stability of the media on which
information is stored, given the enormous economic important of
information, has become widespread in most developed countries.
Within the overall concern regarding the preservation of stored
information, the attention focused on the stability of motion picture
films is of special importance as cultural heritage worth safeguarding.
The cinema archives have focused a great deal of attention on the
scientific knowledge1,2,3,4,5 related to the degradation of the film
materials and their optimum storage conditions in vaults. Many studies
have been directed at the influence of the principal factors that affect
film conservation in the storage environment: temperature, relative
humidity and pollutants. Acting alone, or more frequently acting in
combination, they can have important effect on the deterioration of
gelatine, silver, dyes and polymer supports.
In contrast to the attention given to the chemical stability of
cinematographic film, papers that focus on the biological stability of
the constitutive materials of the films are very scarce. Almost all film
has an emulsion layer of gelatine, which in damp conditions is an ideal
nutrient for micro-organism growth. Also, the polymer supports based
on cellulose material can be susceptible of micro-organism attack.
The evolution 6 of flexible silver-gelatine photographic films began with
cellulose nitrate as the support in 1889. This had excellent physical
properties but its chemical stability was very poor, and also was a fire
hazard. In 1922, amateur movie films were introduced using an organic
ester of cellulose support (cellulose diacetate) because of its slow
burning characteristics. For 30 years, the only commercial safety films
consisted of a variety of organic ester of cellulose such us cellulose
diacetate, cellulose acetate-propionate or cellulose acetate-butyrate.
However, in professional cinematography cellulose nitrate remained
the principal support until 1951. In 1948 cellulose triacetate supports
(CTA) were introduced as this material met all the technical and safety
requirements for professional motion picture films. In the mid-1950s 7
poly(ethylene terephtalate) material (PET, known in the industry as
“polyester”) was introduced and its use began to increase in the 1980s.
Today PET has a wide acceptance due to its exceptional physical
properties as a safety photographic film support. Its structure is
inherently more chemically stable 8 than either cellulose nitrate or
cellulose acetate stability. On accelerated-aging test, PET suggests a
longer life by five to ten times that of CTA under the same comparable
conditions 9 . Currently, cellulose nitrate photographic films are not
acceptable for any film production. Poly(ethylene) terephtalate is
mainly use as cut sheet polyester film (X-ray and graphic arts
37 Journal of Film Preservation / 67 / 2004