Nitrate film
From The Art and Popular Culture Encyclopedia
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Nitrocellulose was used as the first flexible film base, beginning with Eastman Kodak products in August, 1889. Camphor is used as plasticizer for nitrocellulose film. It was used until 1933 for X-ray films (where its flammability hazard was most acute) and for motion picture film until 1951. It was replaced by safety film with an acetate base.
The use of nitrocellulose film for motion pictures led to a widespread requirement for fireproof projection rooms with wall coverings made of asbestos. The US Navy shot a training film for projectionists that included footage of a controlled ignition of a reel of nitrate film, which continued to burn even when fully submerged in water. Due to public safety precautions, the London Underground forbade transport of nitrate films on its system until well past the introduction of safety film.
A cinema fire caused by ignition of nitrocellulose film stock (foreshadowed by an earlier small fire) was a central plot element in the Italian film Cinema Paradiso (1988). Today nitrate film projection is normally highly regulated and requires extensive precautionary measures including extra projectionist health and safety training. In addition, projectors certified to run nitrate films have many containment strategies in effect, among them including the chambering of both the feed and take up reels in thick metal covers with small slits to allow the film to run through. Furthermore, the projector is modified to accommodate several fire extinguishers with nozzles all aimed directly at the film gate; the extinguishers automatically trigger if a piece of flammable fabric placed near the gate starts to burn. While this triggering would likely damage or destroy a significant portion of the projection components, it would prevent a devastating fire, which could cause far greater damage. In addition, projection rooms may be required to have automatically-operating metal covers for the projection windows, preventing the spreading of a fire to the auditorium.
It was found that nitrocellulose gradually decomposes, releasing nitric acid, further catalyzing the decomposition (eventually into a still-flammable powder or goo). Decades later storage at low temperatures was discovered as a means of delaying these reactions indefinitely. It is thought the great majority of films produced during the early twentieth century were lost forever either through this accelerating, self-catalyzed disintegration or through studio warehouse fires. Salvaging old films is a major problem for film archivists (see film preservation).
Nitrocellulose film base manufactured by Kodak can be identified by the presence of the word Nitrate in dark letters between the perforations. Acetate film manufactured during the era when nitrate films were still in use was marked Safety or Safety Film between the perforations dark letters. Letters in white or light colors are print-through from the negative. Film stocks in the non-standard gauges, 8 mm or 16 mm, were not manufactured with a nitrate base.
The material was replaced by polyester or PET film, which is much more resistant to polymer degradation.
