Cellulose acetate film, or safety film, is used in photography as a base material for photographic emulsions. It was introduced in the early 20th Century by film manufacturers as a safe film base replacement for unstable and highly flammable nitrate film.
Beginning with cellulose diacetate in 1909, this innovation continued with cellulose acetate propionate and cellulose acetate butyrate in the 1930s, and finally in the late 1940s, cellulose triacetate was introduced, alongside polyester bases. These less flammable substitutes for nitrate film were called safety film.
The motion picture industry continued to use cellulose nitrate until the introduction of cellulose triacetate in 1948, which met the rigorous safety and performance standards set by the cinematographic industry. The chemical instability of this material, unrecognized at the time of its introduction, has since become a major threat for film collections.
Currently there is no practical way of halting or reversing the course of degradation. While there has been significant research regarding various methods of slowing degradation, such as storage in molecular sieves, temperature and moisture are the two key factors affecting the rate of deterioration. According to the Image Permanence Institute, fresh acetate film stored at a temperature of 65°F (18°C) and 50% relative humidity will last approximately 50 years before the onset of vinegar syndrome. Reducing the temperature 15°, while maintaining the same level of humidity, delays the process by 150 years. A combination of low temperature and low relative humidity represents the optimum storage condition for cellulose acetate base films.
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Source BioScience film archives storage
Moving film to Source BioScience, and improving the storage environment from 16°C/50-60%RH to 5°C/35%RH has very positive preservation implications.
For degrading acetate film, we have increased the time in which free acidity will double from around 10 years to approximately 200 years.
For acetate not yet degrading, we have increased the years it will take for acidity to develop from approximately 80 years to about 350 years.
Non Acetate specific, including polyester
We have increased the Preservation Index from 63 years to 488 and reduced the Natural Age Rate from moderate to very slow. (Preservation Index (PI) is a concept introduced by the Image Permanence Institute in 1995 to express the "preservation quality" of a storage environment for organic materials. PI has units of years. The higher the PI, the better conditions are for preservation of organic materials.)
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