Cellulose acetate film
Encyclopedia
Cellulose acetate
film, or safety film, is used in photography
as a base material for photographic emulsion
s. 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 supports 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.
Company within a decade of its introduction in 1948. The first report came from the Government of India, whose film was stored in hot, humid conditions. It was followed by further reports of degradation from collections stored in similar conditions. These observations resulted in continuing studies in the Kodak laboratories during the 1960s.
Beginning in the 1980s, there was a great deal of focus upon film stability following frequent reports of cellulose triacetate degradation. This material releases acetic acid
, the key ingredient in vinegar
and responsible for its acidic smell. The problem became known as the "vinegar syndrome."
(CH3CO) groups are attached to long molecular chains of cellulose
. With exposure to moisture, heat, or acids, these acetyl groups break from their molecular bonds and acetic acid is released. While the acid is initially released inside the plastic, it gradually diffuses to the surface, causing a characteristic vinegary smell.
The decay process follows this pattern:
, A-D, or "acid-detection" indicator strips change color from blue through shades of green to yellow with increasing exposure to acid. According to the test User's Guide, they were "...created to aid in the preservation of collections of photographic film, including sheet and roll film
s, cinema film, and microfilm. They provide a nondestructive method of determining the extent of vinegar syndrome in film collections." These tools can be used to determine the extent of damage to a film collection and which steps should be taken to prolong their usability.
s, 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, however, in practice temperatures of 55°F (12°C) and a relative humidity of 35% are now being used.
Microenvironments—the conditions inside an enclosure—can also have an impact on the condition of cellulose acetate film. Enclosures that are breathable or that contain an acid absorbent are instrumental in reducing the rate of decay due to vinegar syndrome. Sealed metal containers can trap the decay products released by the film, promoting the spread of vinegar syndrome.
. Once the film becomes brittle it cannot be copied in its entirety. Because the gelatin emulsion usually stays intact during the degradation process, it is possible to save the image on sheet film using solvents to dissolve the emulsion away from the shrunken base. Once the emulsion has been freed from the shrunken support, it can be photographed or transferred to a new support. Because of the solvents used, this is a delicate and potentially hazardous procedure and is an expensive process for a large collection. Degraded motion picture film cannot be restored in this way, but sheet films often can.
While digitization would be an ideal way to preserve the contents of cellulose acetate film, current standards do not allow for scanning at sufficient resolutions to produce a copy of the same picture and sound quality as the original. Currently, the National Film Preservation Institute advocates film-to-film transfer as the best method for film preservation, with the copies stored in proper environmental conditions.
. The techniques were developed for metallographic needs to examine the grain structure of polished metals. Replication
can be used to understand the distribution, for example, of different types of iron in carbon steel samples, or the fine distribution of damage to a sample subject to mechanical wear.
Cellulose acetate
Cellulose acetate , first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters and...
film, or safety film, is used in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
as a base material for photographic emulsion
Photographic emulsion
Photographic emulsion is a light-sensitive colloid, such as gelatin, coated onto a substrate. In silver-gelatin photography, the emulsion consists of silver halide crystals suspended in gelatin, and the substrate may be glass, plastic film, paper or fabric....
s. It was introduced in the early 20th century by film manufacturers as a safe film base
Film base
A film base is a transparent substrate which acts as a support medium for the photosensitive emulsion that lies atop it. Despite the numerous layers and coatings associated with the emulsion layer, the base generally accounts for the vast majority of the thickness of any given film stock...
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
Cellulose triacetate
Cellulose triacetate, also known simply as triacetate, CTA and TAC, is manufactured from cellulose and a source of acetate esters, typically acetic anhydride...
was introduced, alongside polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
bases. These less flammable substitutes for nitrate film were called safety film.
The motion picture industry continued to use cellulose nitrate supports 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.
Decay and the "vinegar syndrome"
The first instance of cellulose triacetate degradation was reported to the Eastman KodakEastman Kodak
Eastman Kodak Company is a multinational imaging and photographic equipment, materials and services company headquarted in Rochester, New York, United States. It was founded by George Eastman in 1892....
Company within a decade of its introduction in 1948. The first report came from the Government of India, whose film was stored in hot, humid conditions. It was followed by further reports of degradation from collections stored in similar conditions. These observations resulted in continuing studies in the Kodak laboratories during the 1960s.
Beginning in the 1980s, there was a great deal of focus upon film stability following frequent reports of cellulose triacetate degradation. This material releases acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
, the key ingredient in vinegar
Vinegar
Vinegar is a liquid substance consisting mainly of acetic acid and water, the acetic acid being produced through the fermentation of ethanol by acetic acid bacteria. Commercial vinegar is produced either by fast or slow fermentation processes. Slow methods generally are used with traditional...
and responsible for its acidic smell. The problem became known as the "vinegar syndrome."
The progression of degradation
In acetate film, acetylAcetyl
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...
(CH3CO) groups are attached to long molecular chains of cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
. With exposure to moisture, heat, or acids, these acetyl groups break from their molecular bonds and acetic acid is released. While the acid is initially released inside the plastic, it gradually diffuses to the surface, causing a characteristic vinegary smell.
The decay process follows this pattern:
- Acetic acid is released during the initial acetate base deterioration, leading to the characteristic vinegar odor. This signal marks the progression of deterioration.
- The plastic film baseFilm baseA film base is a transparent substrate which acts as a support medium for the photosensitive emulsion that lies atop it. Despite the numerous layers and coatings associated with the emulsion layer, the base generally accounts for the vast majority of the thickness of any given film stock...
becomes brittle. This occurs in the advanced stages of deterioration, weakening the film and causing it to shatter with the slightest tension. These physical changes happen because cellulose acetate consists of long chains of repeating units, or polymerPolymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
s. When the acetic acid is released as these groups break off, the acidic environment helps to break the links between units, shortening the polymerPolymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
chains and leading to brittleness.
- Shrinkage also occurs during this process. With the cellulose acetate polymer chains breaking into smaller pieces, and with their side groups splitting off, the plastic film begins to shrink. In advanced stages of deterioration, shrinkage can be as much as 10%. A 1% reduction in size renders motion picture film unusable.
- As the acetate base shrinks, the gelatinGelatinGelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
emulsionEmulsionAn emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
of the film does not shrink, because it is not undergoing deterioration. The emulsion and film base separate, causing bucklingBucklingIn science, buckling is a mathematical instability, leading to a failure mode.Theoretically, buckling is caused by a bifurcation in the solution to the equations of static equilibrium...
, referred to by archivists as 'channelling.' Sheet filmSheet filmSheet film is large format and medium format photographic film supplied on individual sheets of acetate or polyester film base rather than rolls. Sheet film was initially supplied as an alternative to glass plates...
s are often severely channelled in the later stages of degradation.
- Crystalline deposits or liquid-filled bubbles appear on the emulsion. These are evidence of plasticizers, additives to the plastic base, becoming incompatible with the film base and oozing out on the surface. This discharge of plasticizers is a sign of advanced degradation.
- In some cases, pink or blue colors appear in some sheet films. This is caused by antihalation dyes, which are normally colorless and incorporated into the gelatin layer. When acetic acid is formed during deterioration, the acidic environment causes the dyes to return to their original pink or blue color.
Testing for degradation
A testing product developed by the Image Permanence InstituteImage Permanence Institute
The Image Permanence Institute is a university-based, non-profit research laboratory devoted to scientific research in the preservation of visual and other forms of recorded information. It is the world's largest independent laboratory with this specific scope...
, A-D, or "acid-detection" indicator strips change color from blue through shades of green to yellow with increasing exposure to acid. According to the test User's Guide, they were "...created to aid in the preservation of collections of photographic film, including sheet and roll film
Roll film
Rollfilm or roll film is any type of spool-wound photographic film protected from white light exposure by a paper backing, as opposed to film which is protected from exposure and wound forward in a cartridge. Confusingly, roll film was originally often referred to as "cartridge" film because of its...
s, cinema film, and microfilm. They provide a nondestructive method of determining the extent of vinegar syndrome in film collections." These tools can be used to determine the extent of damage to a film collection and which steps should be taken to prolong their usability.
Preservation and storage
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 sieveMolecular sieve
A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.Molecules small enough to pass through the pores are adsorbed while larger molecules are not. It is different from a common filter in that it operates on a...
s, temperature and moisture are the two key factors affecting the rate of deterioration. According to the Image Permanence Institute
Image Permanence Institute
The Image Permanence Institute is a university-based, non-profit research laboratory devoted to scientific research in the preservation of visual and other forms of recorded information. It is the world's largest independent laboratory with this specific scope...
, 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, however, in practice temperatures of 55°F (12°C) and a relative humidity of 35% are now being used.
Microenvironments—the conditions inside an enclosure—can also have an impact on the condition of cellulose acetate film. Enclosures that are breathable or that contain an acid absorbent are instrumental in reducing the rate of decay due to vinegar syndrome. Sealed metal containers can trap the decay products released by the film, promoting the spread of vinegar syndrome.
Rescuing damaged film
During early stages of decay, the film content can be rescued by transferring it to new film stockFilm stock
Film stock is photographic film on which filmmaking of motion pictures are shot and reproduced. The equivalent in television production is video tape.-1889–1899:...
. Once the film becomes brittle it cannot be copied in its entirety. Because the gelatin emulsion usually stays intact during the degradation process, it is possible to save the image on sheet film using solvents to dissolve the emulsion away from the shrunken base. Once the emulsion has been freed from the shrunken support, it can be photographed or transferred to a new support. Because of the solvents used, this is a delicate and potentially hazardous procedure and is an expensive process for a large collection. Degraded motion picture film cannot be restored in this way, but sheet films often can.
While digitization would be an ideal way to preserve the contents of cellulose acetate film, current standards do not allow for scanning at sufficient resolutions to produce a copy of the same picture and sound quality as the original. Currently, the National Film Preservation Institute advocates film-to-film transfer as the best method for film preservation, with the copies stored in proper environmental conditions.
Other uses
Cellulose acetate film is also used to make replicates of materials and biological samples for microscopyMicroscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
. The techniques were developed for metallographic needs to examine the grain structure of polished metals. Replication
Replication (metallography)
Replication, in metallography, is the use of thin plastic films to nondestructively duplicate the microstructure of a component. The film is then examined at high magnifications....
can be used to understand the distribution, for example, of different types of iron in carbon steel samples, or the fine distribution of damage to a sample subject to mechanical wear.
Further reading
- Adelstein, P.Z., J.M. Reilly, D.W. Nishimura, and C.J. Erbland. “Stability of Cellulose Ester Base Photographic Film: Part I-Laboratory Testing Procedures.” SMPTE Journal 101 no. 5 (May 1992): 336-346.
- Adelstein, P.Z., J.M. Reilly, D.W. Nishimura, and C.J. Erbland. “Stability of Cellulose Ester Base Photographic Film: Part II-Practical Storage Considerations.” SMPTE Journal 101 no. 5 (May 1992): 347-354.
- Adelstein, P.Z., J.M. Reilly, D.W. Nishimura, and C.J. Erbland. “Stability of Cellulose Ester Base Photographic Film: Part III-Measurement of Film Degradation.” SMPTE Journal 104 (May 1995): 281-291.
- Adelstein, P.Z., J.M. Reilly, D.W. Nishimura, C.J. Erbland, and J.L. Bigourdan. “Stability of Cellulose Ester Base Photographic Film: Part V- Recent Findings.” SMPTE Journal 104 no. 7 (July 1995): 439-447.
- Allen, N.S., M. Edge, C.V. Horie, T.S. Jewitt, and J.H. Appleyard. “The Degradation and Stabilization of the Historic Cellulose acetate/ Nitrate Base Motion-picture Film.” The Journal of Photographic Science 36 no.3 (1988): 103-106.
- Allen, N.S., M. Edge, C.V. Horie, T.S. Jewitt, and J.H. Appleyard. “Degradation of Historic Cellulose Triacetate Cinematograph Film: Influence of Various Film Parameters and Prediction of Archival Life.” The Journal of Photographic Science 36 no. 6 (1998), 194-198.
- Allen, N.S., M. Edge, C.V. Horie, T.S. Jewitt, and J.H. Appleyard. “The Degradation Characteristics of Archival Cellulose Triacetate Base Cinematograph Film.” The Journal of Photographic Science 36 no. 6 (1998), 199-203.
- Allen, N.S., M. Edge, T.S. Jewitt, and C.V. Horie. “Initiation of the Degradation of Cellulose Triacetate Base Motion Picture Film.” The Journal of Photographic Science 38 no. 2 (1990): 54-59.
- Allen, N.S., J.H. Appleyard, E. Edge, D. Francis, C.V. Horie, and T.S. Jewitt. “The Nature of the Degradation of Archival Cellulose-Ester Base Motion-Picture Film: The Case for Stabilization.” The Journal of Photographic Science 36 no.2 (1988): 34-39.
- Allen, N.S., M. Edge, T.S. Jewitt, and C.V. Horie. “Stabilization of Cellulose Triacetate Base Motion Picture Film.” The Journal of Photographic Science 30 no.1 (1990):26-29.
- Bigourdan, Jean-Louis and James M. Reilly. “Effectiveness of storage Conditions in Controlling the Vinegar syndrome: Preservation Strategies for Acetate Base Motion-Picture Film Collections.” In Michelle Aubert and Richard Billeaud. Archiver et communiquer l'image et le son :les enjeux du 3ème millenaire : actes du Symposium Technique Mixte—JTS Paris 2000, 14-43. Paris: CNC, 2000.
- Edge, M. and N.S. Allen. “Fundamental Aspects of the Degradation of Cellulose Triacetate Base Cinematograph Film.” Polymer Degradation and Stability 25 no. 2-4 (1989): 345-362.
- Horvath, David G. (1987). The Acetate Negative Survey Final Report. Louisville, KY: Ekstrom Library Photographic Archives, University of Louisville. http://louisville.edu/library/ekstrom/special/files/Acetates
- Meyer, Mark-Paul and Paul Read. “Restoration and Preservation of Vinegar Syndrome Decayed Acetate Film.” In Michelle Aubert and Richard Billeaud. Archiver et communiquer l'image et le son :les enjeux du 3ème millenaire : actes du Symposium Technique Mixte—JTS Paris 2000, 54-65. Paris: CNC, 2000.
- National Film Preservation Foundation. The Film Preservation Guide: The Basics for Archives, Libraries, and Museums. San Francisco: National Film Preservation Foundation, 2004.
- Ram, A.T. “Archival Preservation of Photographic Films-A Perspective.” Polymer Degradation and Stability 29 no. 1 (1990): 3-29.
- Ram, A.T., D.F. Kopperl, and R.C. Sehlin. “The Effects and Prevention of Vinegar Syndrome.” The Journal of Imaging science and Technology 38 no. 3 (1994): 249-261.
- Reilly, James M. “Basic Strategy for Acetate Film Preservation.” Microform and Imaging Review 31 no. 4 (2002): 117-130.
- Reilly, James M. IPI Storage Guide for Acetate Film; Instructions of Using the Wheel, Graphs, and Table; Basic Strategy for Film Preservation. Rochester: Image Permanence Institute, 1993.