Cellulose acetate film

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Ilford HP5 Plus Safety Film

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 and intended as a safe film base replacement for unstable and highly flammable nitrate film.

Contents

Cellulose diacetate film was first employed commercially for photographic film in 1909. Cellulose acetate propionate and cellulose acetate butyrate were introduced in the 1930s, and cellulose triacetate in the late 1940s. Acetate films were later replaced by polyester bases.

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. [1] The chemical instability of cellulose acetate material, unrecognized at the time of its introduction, has since become a major problem for film archives and collections. Digitization is now the best way to preserve the contents of cellulose acetate film.

History

Cellulose diacetate film was first created by the German chemists Arthur Eichengrün and Theodore Becker, who patented it under the name Cellit, from a process they devised in 1901 for the direct acetylation of cellulose at a low temperature to prevent its degradation, which permitted the degree of acetylation to be controlled, thereby avoiding total conversion to its triacetate. Cellit was a stable, non-brittle cellulose acetate polymer that could be dissolved in acetone for further processing. A cellulose diacetate film more readily dissolved in acetone was developed by the American chemist George Miles in 1904. Miles's process (partially hydrolysing the polymer) was employed commercially for photographic film in 1909 by Eastman Kodak and the Pathé Frères. Starting with cellulose diacetate, this innovation continued with cellulose acetate propionate and cellulose acetate butyrate in the 1930s, and finally in the late 1940s, cellulose triacetate was introduced, and later polyester bases. [2] These less flammable substitutes for nitrate film were called safety film.

Boroid

BOROID advertisement 'The Stage'

In 1910, a newly discovered, non-inflammable, film format 'BOROID' was presented to the British cinematographic trade using acetate-based cellulose. It was developed, he claimed 'accidentally', by the prolific inventor Benno Borzykowski, a partner in Photochemie G.m.b.H. Berlin, and Director of the Benobor Syndicate, who had worked on other patents for artificial silk and other fabrics. BOROID was a by-product of that work by Borzykowski, but was not patented. ("The process has not been patented and will not be; it is a secret formula known only to the inventor and two trustees in England. He has never sold the process itself, merely the right to manufacture and market…" [3] )

Borzykowski published other UK patents including "Original printed patent application number 21,719 for a new or improved process for the production of a substitute for glass sheets or plates and other articles…" in 1910. The Boroid company commenced trading on 21 November 1910, being originally registered in London at 58 Coleman St., moving to 104 High Holborn in May 1911, and finally to 48 Rupert St. in June 1913.

Boroid Ltd. issued its detailed share prospectus in the (Westminster Gazette of Monday 16 January 1911 (P12 col. 1 and 2): A number of testimonials were provided, including a very detailed one from Alfred J West F.R.G.S. of 'Our Navy', in which he proposed to move his entire production to 'non-flam' BOROID film: 'BOROID' had most of its assets in Germany, and the Great War of 1914-1919 put an immediate end to the business in the UK when BOROID film stock became unavailable. A Receiver was appointed by the debenture holders on 12 May 1914 (The London Project). Borzykowski moved to America and was interviewed in an article in the Educational Film Magazine in the April 1919 edition. [3]

Decay and the "vinegar syndrome"

Shrinking and warpage of 16 mm film caused by vinegar syndrome Vinegar Syndrome D.D. Teoli Jr (2).jpg
Shrinking and warpage of 16 mm film caused by vinegar syndrome

Beginning in the 1980s, there was a great deal of focus upon film stability following frequent reports of cellulose triacetate degradation. Cellulose acetate releases acetic acid, the key ingredient in vinegar, which is responsible for its acidic smell. The problem became known as "vinegar syndrome". [4] This accelerates degradation within the film, and can also contribute to damage to surrounding films and metals. [5]

The first instance of cellulose triacetate degradation was reported to the Eastman Kodak Company within a decade of its introduction in 1948. The first report came from the Government of India, whose film materials were 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. Film degradation can only be delayed by storage in dry and cold conditions. It was initially thought that storage under recommended conditions might delay decay by 450 years, but some films are developing vinegar syndrome after just 70 years of cold dry storage. [5] Arri and others sold film recorders specifically for recording video onto film for archival purposes based on the assumption that vinegar syndrome could be delayed for long periods of time. [6] [7]

Testing for degradation

A testing product developed by the Image Permanence Institute, 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 films, cinema film, and microfilm. They provide a nondestructive method of determining the extent of vinegar syndrome in film collections." [8] 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. Many film collectors use camphor tablets but it is not known what the long term effects on the film would be. [9] 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 21 °C (70 °F) and 40% relative humidity will last approximately 50 years before the onset of vinegar syndrome. Reducing the temperature by −9 °C (15 °F) while maintaining the same level of humidity brings a dramatic improvement: at a temperature of 13 °C (55 °F) and 40% relative humidity, the estimated time until onset of vinegar syndrome is 150 years. [10] A combination of low temperature and low relative humidity represents the optimum storage condition for cellulose acetate base films, [11] with the caveat that relative humidity should not be lowered below 20%, or the film will dry out too much and become brittle. [12]

Cold storage options for the preservation of acetate film range from insulated cold storage rooms, or vaults, with relative humidity control (typical settings in the range of 2–4 °C (35–40 °F) temperature, and 30–35% relative humidity), which might be used by archival institutions for large and medium-sized collections, to free-standing freezer units, which can be cost-effective for small collections, but necessitate vapor-proof packaging of the films to protect against relative humidity extremes and condensation. [13] [14] Commercial storage facilities may offer varying environmental conditions at different rates. [15] [16]

Microenvironments—the conditions inside an enclosure—can also affect 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. [17]

Rescuing damaged film

During early stages of decay, the film content can be rescued by transferring it to new film stock. Once the film becomes too brittle or the shrinkage is excessive, it cannot be copied. 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 base off the emulsion. 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. [18]

Digitization is now the best way to preserve the contents of cellulose acetate film. Current standards now allow for scanning at more than ample resolution to produce a copy of the same picture and sound quality as the original. Transfer processes at 10K (pixel) resolution are not uncommon. Transferring is now done without film-damaging sprocket transport, hence, the original film stock suffers little, if any, damage. The Godfather trilogy is one of the best and earliest examples of full resolution digital transfer and ultimate restoration. This seminal project was completed several years ago, and the process has significantly improved since then.

4K digital resolution, often available for home viewing, will deliver quality equal to an original analogue 35 mm film. The 10K transfer resolution standard seems to accommodate most, or all 65–75 mm wide-screen variants. These film variants were developed in the 1950s and 1960s, (e.g., Spectra-vision, Vista-Vision, CinémaScope, etc.)[ citation needed ]

Other uses

Cellulose acetate film is also used to make replicates of materials and biological samples for microscopy. 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. [19] [20]

Related Research Articles

<span class="mw-page-title-main">Film stock</span> Medium used for recording motion pictures

Film stock is an analog medium that is used for recording motion pictures or animation. It is recorded on by a movie camera, developed, edited, and projected onto a screen using a movie projector. It is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast and resolution of the film. The emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use. Instead, a very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, all films are sensitive to X-rays and high-energy particles. Most are at least slightly sensitive to invisible ultraviolet (UV) light. Some special-purpose films are sensitive into the infrared (IR) region of the spectrum.

<span class="mw-page-title-main">Nitrocellulose</span> Highly flammable compound

Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and sulfuric acid. One of its first major uses was as guncotton, a replacement for gunpowder as propellant in firearms. It was also used to replace gunpowder as a low-order explosive in mining and other applications. In the form of collodion it was also a critical component in an early photographic emulsion, the use of which revolutionized photography in the 1860s.

<span class="mw-page-title-main">Film preservation</span> Historic preservation of motion pictures

Film preservation, or film restoration, describes a series of ongoing efforts among film historians, archivists, museums, cinematheques, and non-profit organizations to rescue decaying film stock and preserve the images they contain. In the widest sense, preservation assures that a movie will continue to exist in as close to its original form as possible.

<span class="mw-page-title-main">Cellulose acetate</span> Organic compounds which are acetate esters of cellulose

In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and as a frame material for eyeglasses; it is also used as a synthetic fiber in the manufacture of cigarette filters and playing cards. In photographic film, cellulose acetate film replaced nitrate film in the 1950s, being far less flammable and cheaper to produce.

<span class="mw-page-title-main">Cellulose triacetate</span> Chemical compound

Cellulose triacetate, triacetate, CTA or TAC is a chemical compound produced from cellulose and a source of acetate esters, typically acetic anhydride. Triacetate is commonly used for the creation of fibres and film base. It is chemically similar to cellulose acetate. Its distinguishing characteristic is that in triacetate, at least "92 percent of the hydroxyl groups are acetylated." During the manufacture of triacetate, the cellulose is completely acetylated; whereas in normal cellulose acetate or cellulose diacetate, it is only partially acetylated. Triacetate is significantly more heat resistant than cellulose acetate.

<span class="mw-page-title-main">Vinegar syndrome</span>

Vinegar syndrome, also known as acetic acid syndrome, is a condition created by the deacetylation of cellulose acetates and cellulose triacetate. This deacetylation produces acetic acid, giving off a vinegar odor that gives the condition its name; as well, objects undergoing vinegar syndrome often shrink, become brittle, and form crystals on their surface due to the migration of plasticizers. Vinegar syndrome widely affects cellulose acetate film as used in photography. It has also been observed to affect older magnetic tape, where cellulose acetate is used as a base, as well as polarizers used in liquid-crystal display units and everyday plastics such as containers and tableware. High temperatures and fluctuations in relative humidity have been observed to accelerate the process. The process is autocatalytic, and the damage done by vinegar syndrome is irreversible.

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<span class="mw-page-title-main">Cellulose diacetate</span> Chemical compound

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References

  1. ↑ Ram, A. Tulsi (1990). "Archival Preservation of Photographic Film-A Perspective". Polymer Degradation and Stability. 29 (1): 4. doi:10.1016/0141-3910(90)90019-4. ISSN   0141-3910.
  2. ↑ National Film Preservation Foundation (2004). The Film Preservation Guide: The Basics for Archives, Libraries, and Museums. San Francisco: National Film Preservation Foundation. p. 9. ISBN   9780974709901. Archived from the original on 14 April 2019. Retrieved 5 January 2013.
  3. 1 2 Educational Film Magazine in the April 1919 edition (p. 22-25. p. 136 in the linked PDF file)
  4. ↑ Adelstein, P.Z.; Reilly, J.M.; Nishimura, D.W. & Erbland, C.J. (May 1992). "Stability of Cellulose Ester Base Photographic Film: Part I-Laboratory Testing Procedures". SMPTE Motion Imaging Journal. 101 (5): 336. doi:10.5594/J02284. ISSN   1545-0279.
  5. 1 2 Ahmad, Ida R. (19 May 2020). "Historical films may be decaying much faster than we thought thanks to 'vinegar syndrome'". The Conversation.
  6. ↑ Laser recording system colour microfilm creating digital copies tate.org.uk
  7. ↑ "Filmmaker Stories".
  8. ↑ Image Permanence Institute (2001). User's Guide for A-D Strips: Film Base Deterioration Monitor. Rochester, NY: Image Permanence Institute.
  9. ↑ Allen, N.S.; Edge, M.; Horie, C.V.; Jewitt, T.S. & Appleyard, J.H. (1998). "Degradation of Historic Cellulose Triacetate Cinematograph Film: Influence of Various Film Parameters and Prediction of Archival Life". The Journal of Photographic Science. 36 (6): 194. doi:10.1080/00223638.1988.11736999. ISSN   0022-3638.
  10. ↑ Reilly, James M. (1993). IPI Storage Guide for Acetate Film: Instructions for Using the Wheel, Graphs, and Table: Basic Strategy for Film Preservation. Rochester: Image Permanence Institute. pp. 5–6. OCLC   28283222.
  11. ↑ Adelstein, P.Z.; Reilly, J.M.; Nishimura, D.W. & Erbland, C.J. (May 1992). "Stability of Cellulose Ester Base Photographic Film: Part II-Practical Storage Considerations". SMPTE Motion Imaging Journal. 101 (5): 353. doi:10.5594/J02285. ISSN   1545-0279.
  12. ↑ Reilly (1993), p. 4.
  13. ↑ National Film Preservation Foundation (2004). The Film Preservation Guide: The Basics for Archives, Libraries, and Museums. San Francisco: National Film Preservation Foundation. p. 62. Archived from the original on 14 April 2019. Retrieved 5 January 2013.
  14. ↑ Wagner, Sarah S. (2007). "Cold Storage Options: Costs and Implementation Issues" (PDF). Topics in Photographic Preservation. 12: 224–238. ISSN   1048-4388. Archived (PDF) from the original on 28 April 2021.
  15. ↑ Wagner (2007), p. 226; The Film Preservation Guide (2007), p. 63–64.
  16. ↑ "Film and Media Storage". Bonded Services Group. Archived from the original on 14 September 2010.
  17. ↑ Bigourdan, Jean-Louis & Reilly, J. (May 2000). "Effectiveness of Storage Conditions in Controlling the Vinegar Syndrome: Preservation Strategies for Acetate Base Motion-Picture Film Collections". In Aubert, Michelle & Billeaud, Richard (eds.). Archiver et communiquer l'image et le son: les enjeux du 3ème millenaire. Joint Technical Symposium Paris 2000. Paris: CNC. pp. 14–34. ISBN   9782910202033. Archived from the original (PDF) on 16 September 2019.
  18. ↑ Reilly, James M (November 2007). "Basic Strategy for Acetate Film Preservation". Microform and Imaging Review. 31 (4): 118. doi:10.1515/MFIR.2002.117. ISSN   0949-5770. S2CID   161088393.
  19. ↑ Vander Voort, G.F. & Roósz, A. (February 1984). "Measurement of the Interlamellar Spacing of Pearlite". Metallography. 17 (1): 1–17. doi:10.1016/0026-0800(84)90002-8. ISSN   0026-0800.
  20. ↑ Higham, P.A.; Stott, F.H. & Bethune, B. (1978). "Mechanisms of Wear of the Metal Surface During Fretting Corrosion of Steel on Polymers". Corrosion Science. 18 (1): 3–13. doi:10.1016/S0010-938X(78)80071-7. ISSN   0010-938X.

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