A look at cellulose acetate film - An academic paper

source:http://blog.thepreservationlab.org/2014/07/incendiary-films/

Beginning from the 1890s, the development of film stock coincided with the growth of the motion picture industry in the United States. Consequently, manufacturers had introduced a variety of film stock in responding to customer concerns and grievances. Since the inception of film stock production, three types of film bases have been developed. In chronological order, these three film bases were cellulose nitrate, cellulose acetate and polyester. Both cellulose acetate and polyester were introduced in an effort to deal with the shortcomings of the film base which preceded them. This research paper would examine various aspects of cellulose acetate film stock as an archival media format.

                                           In the 1890s, cellulose nitrate was the only available transparent plastic film base which was durable enough to be used with movie cameras and projectors[1]. However, in spite of its strength and flexibility, nitrate-based film was a serious hazard because of its combustibility. Furthermore, nitrate fires were difficult, if not impossible, to extinguish once ignited. In fact, the combustible nature of cellulose film accounted partly for the loss many films made in the United States between 1893 and 1950. In due course, the need arose for the development of a safer film medium and efforts were made to make this possible.

                                        Eventually, manufacturers were able to discover a safe substitute for cellulose nitrate by exploring various plastics in the cellulose acetate family[2]. Beginning in 1909 with cellulose diacetate, a number of new acetate bases were subsequently introduced over a period of time - in the 1930s there was cellulose acetate propionate and cellulose acetate butyrate. Finally, in the late 1940s cellulose triacetate was developed. Each acetate discovery improved upon the technical deficiencies of its predecessor[3]. Cellulose acetate propionate and cellulose acetate butyrate improved upon the physical frailty of cellulose diacetate, though none of them were as durable as cellulose triacetate[4]. Indeed, cellulose triacetate, because of the improvements it embodied, was viewed as the final answer to the question of finding a suitable replacement for cellulose nitrate. Whilst earlier cellulose acetate bases were incorporated in manufacturing 8mm and 16mm film stock, cellulose triacetate was commonly used in 35mm studio films in the late 1940s[5]. Acetate film stock, due to its development as a safe alternative to cellulose nitrate, was marketed as safety film by manufacturers. In fact,  acetate film stock that was produced by Kodak often had the words SAFETY FILM printed along the edge of the film[6]. Currently, a considerable amount of the film found in libraries, historical collections, archives, and personal film collections were made from cellulose acetate[7].

                                     Acetate base varies chemically from nitrate base. As aforementioned, it is neither inflammable nor does it emit gases that can cause combustion, unlike cellulose nitrate. However, the molecular compounds inherent in acetate render it susceptible to a number of other chemical reactions which can hasten its deterioration, if due care is not taken. To create cellulose acetate, acetyl groups are grafted unto cellulose molecules. However in the presence of moisture, acids and heat the acetyl groups can detach from the cellulose molecules triggering a number of chemical reactions. Acetic acid is released inside the plastic and gradually diffuses to the surface producing a sharp vinegar odor. This chemical reaction is called vinegar syndrome. It is estimated that 1000-ft. of 35 mm film can generate an ample amount of acetic acid to be the equivalent of 250 teaspoonfuls of household vinegar[8]. The acetic acid which is released can affect other film stock in close proximity. As such, deteriorating acetate film has to be separated from other films.                            

                                       Though vinegar syndrome is the most evident sign of acetate base deterioration, it is not the only indicator. In advanced stages of deterioration, the embrittlement of the plastic base can take place where material, that was previously flexible and strong, transforms into a frail one that can easily shatter with the slightest bending. Cellulose acetate is called a long chain polymer because consists of long chains of repeating units[9]. When acetic acid is released and the acetyl side groups come off, the resultant acidic environment aids in breaking the links between the units. This breakage shortens the polymer chains and causes brittleness. Shrinkage is another consequence of acetate-based deterioration and also occurs when the acetate polymer chains split into smaller pieces and the acetyl side groups begin breaking off[10]. As a result, the plastic film shrinks. Certain levels of shrinkage are manageable and even a natural occurrence since small amounts of shrinkage can occur over a period of time through loss of solvents in the film base. However, the really destructive shrinkage, which can cause serious problems for archivists, usually occurs because of vinegar syndrome. The appearance of crystalline buildups and liquid-filled bubbles on the gelatin emulsion is another indicator of decomposition. This occurs because of the escaping of plasticizers from the film base to the surface of the emulsion. These plasticizers, which make up between 12% and 15% of the film weight, are additives used to stymie the burning rate of acetate film if it catches fire[11]. Plasticizers also serve to reduce the dimensional instability of acetate film which can be affected by solvent loss or humidity change[12]. The appearance of these plasticizers on the surface of the film base is associated with the more advanced stages of degradation. Yet another sign of acetate deterioration brought on by vinegar syndrome is color fading which particularly affects color acetate film. Color film consists of a variety of dyes, which each fade at different times. Signs of color fading may include changes in color, loss of contrast and balance, and a faded look. Some acetate film may even have a pink look. This is indicative of the final stage color degradation since the magenta dye is usually the last one to fade. These myriad of chemical imbalances, physical reactions and visual alterations are all indicative of some degree of film degradation. More so, they can be used as guide as how much degradation has taken place and what preservation techniques can be used to prevent further damage.

                                            Perhaps the most popular means of preserving acetate film is achieved by ensuring proper storage temperature and other environmental controls including ventilation and humidity[13]. The warmer the temperature, the faster cellulose acetate film will deteriorate. The colder the temperature, the more the compounds in the film base will stabilize thus delaying deterioration. For instance, color film is especially prone to fading if kept in heated areas[14]. The Image Permanence Institute’s (IPI) research on film preservation was able to show that if acetate film was kept at 70°F and 60% relative humidity (RH), it will reach significant levels of acidity after about 40 to 50 years of storage[15]. Furthermore, the ideal storage conditions for the long-term preservation of acetate film are at a freezing 32°F[16]. However, reducing and maintaining this temperature can be costly depending on the resources of the archive. For large and medium-sized collections, insulated cold storage rooms with humidity control and ventilation is often used. For archives or even libraries with smaller collections and a lesser budget, freezers or refrigerators can be used although film has to be properly packaged to protect against the effects of high humidity[17]. It is important that such storage spaces not be used as work spaces for other activities[18]. It is also advisable that acetate film be stored separately from nitrate film[19].  Due care must also be taken to ensure that deteriorating acetate stock is not in close proximity to others. Still, the control of temperature and relative humidity is the most economical method of preservation. Adherence to certain quality controls can give an archivist valuable time in deciding what measures can be undertaken to copy or transfer material that may have already begun to deteriorate[20].

                               Another strategy archivists use to preserve the content of film is reformatting. Reformatting can be used for preservation as well as for access. Reformatting for access entails producing duplicates of the original film and using these duplicates for public use. Thus, the original is spared the rigors of public access. Reformatting for preservation entails transferring source material from one unstable format to a more robust one. In the case of cellulose acetate film, transferals are done unto polyester film format. However, reformatting can be a costly undertaking for archives since it demands high specialized labor that is usually privately contracted by the archive. Librarians and archivists must decide which film in their collections merit preservation and thus carefully consider the value of all their films[21]. Many times the final decision on which film to transfer may not even be made by a librarian or archivists, but rather a particular financial donor who may have some personal interest in seeing a specific film be preserved. This scenario is compounded by the reality that many libraries and archives are experiencing tremendous financial difficulties and may have to submit to the wishes of donors and sponsors. Author Caroline Frick describes this state of affairs as the “politics of preservation”[22]. The capability of archivists and librarians to carry out their mandate of preservation for all items has always been compromised by the interest of those who finance their operations. Such issues can determine how a film might be preserved, what film might be preserved and to what extent will funding be made available to make it accessible to the public.

                                  The development of cellulose acetate as a film format needs to be recognized and celebrated when examining the history of film preservation in the United States. Its widespread use from the 1940s coincided with a growing realization that the film heritage of the United States needed to be preserved as well as other concerns about the hazards of cellulose nitrate film. In spite of the eventual realization if its instability, I believe that it represents that transition phase between the introduction of cellulose nitrate film and the discovery of polyester film as a final answer to our film preservation concerns. Cellulose acetate’s importance in the film preservation heritage of the United States warranted an examination of it as a film format.

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[1] The film preservation guide: the basics for archives, libraries, and museums. (San Francisco, Calif.: National Film Preservation Foundation, 2004)8.

[2] The film preservation guide, 9.

[3] The film preservation guide, 9.

[4] The film preservation guide ,9.

[5] “Washington State Preservation Manual.” accessed January 30, 2013. http://www.lib.washington.edu/specialcollections/collections/film-preservation-manual/

[6] Washington State Preservation Manual.

[7] Washington State Preservation Manual.

[8] IPI storage guide for acetate film : instructions for using the wheel, graphs, and table : basic strategy for film preservation. (Rochester, NY. : Image Permanence Institute, Rochester Institute of Technology, 1993), 10.

[9] IPI storage guide for acetate film, 11.

[10] IPI storage guide for acetate film, 11.

[11] IPI storage guide for acetate film, 12.

[12] IPI storage guide for acetate film, 12.

[13] Bowser, Eileen, and John Kuiper. A handbook for film archives. (Brussels, Belgium: FIAF Secretariat, 1980), 22.

[14] “Washington State Preservation Manual.”

[15] Gracy, Karen, and Michèle Cloonan. "The preservation of moving images." Advances in librarianship 27 (2004): 38, accessed January 24, 2013.

[16] The film preservation guide, 60.

[17] The film preservation guide, 62.

[18] The film preservation guide, 62.

[19] Bowser and Kuiper, A handbook for film archives, 22.

[20] Gracy and Cloonan. "The preservation of moving images," 39.

[21] Gracy and Cloonan. "The preservation of moving images," 42.

[22] Frick, Caroline. Saving Cinema: The Politics of Preservation: The Politics of Preservation. (Oxford University Press, USA, 2011)3.

Bibliography

Bowser, Eileen, and John Kuiper. A handbook for film archives. Brussels,Belgium: FIAF Secretariat, 1980.

This book gave a very insightful look at certain issues surrounding cellulose acetate. It was specifically chosen because of its 1980 publishing date in order to get a better idea of the attitudes towards the issue of film preservation.

Harrison, Helen. Film Library Techniques. New York, Hastings House, 1973.

This book was also chosen because of the time period it was published. Its look at preservation techniques at the time allowed me to compare with other material how methods have changed.

Frick, Caroline. Saving Cinema: The Politics of Preservation: The Politics of Preservation. USA: Oxford University Press, 2011.

This book dealt extensively with many of the non-archival issues pertaining to the preservation and access of film. Though much material was not taken from it, it still proved useful in providing a different perspective.

Gracy, Karen F. Film preservation: competing definitions of value, use, and practice. Chicago, IL : Society of American Archivists, 2007.

Karen Gracy has written extensively on film preservation, its history and other issues surrounding it. I actively sought out any material written by her to inform my understanding on the topic.

Gracy, Karen F., and Michèle Valerie Cloonan. "The preservation of moving images." Advances in Librarianship 27 (2004): 1-77. Accessed January 28, 2013.

This paper by Karen Gracy may have been the prelude the her book in 2007 on film preservation. It also deal with the topic extensively.