Black and white negatives on plastic support
| Page Information | |
| Date initiated | March 2023 |
| Contributors | Sarah Casto, Luisa Casella |
Black and white negatives on plastic support[edit | edit source]
Historical Facts[edit | edit source]
Photographic negatives have evolved significantly since their inception. Initially captured on paper and glass substrates, the discovery of cellulose nitrate in the 1840s revolutionized the medium, leading to the production of flexible, lightweight film bases like cellulose acetate and polyester. These materials enabled easier handling and broader use in both professional and amateur photography. Major developments included the collodion process in the early 1850s, the introduction of gelatin as a binder in 1871 by Richard Leach Maddox, and the widespread adoption of cellulose acetate and polyester film bases in the mid-20th century due to their stability and safety.
Identification Characteristics[edit | edit source]
Black and white negatives on plastic supports can be identified by their physical characteristics and deterioration signs. These negatives, typically made from cellulose nitrate, cellulose acetate, or polyester, exhibit various forms of degradation, such as brittleness, discoloration, and shrinkage, which are crucial for their identification and subsequent conservation efforts.
Image material[edit | edit source]
Developed silver is the primary image material in black and white negatives. This material interacts with light to capture and develop the photographic image, encapsulated within a gelatin binder on the film base. The image quality and durability heavily depend on the type of plastic support and the conditions under which the negative is stored.
Color[edit | edit source]
Monochromatic tones characterize black and white photographic negatives. These tones range from deep blacks to various shades of gray.
Support[edit | edit source]
The support for these negatives has transitioned from paper and glass in the early days of photography to various types of plastics, such as cellulose nitrate, cellulose acetate, and polyester. Each material has distinct handling, preservation, and storage requirements due to its chemical stability and physical properties.
Polyester supports can be identified using a cross polarized filter[1].
Deterioration[edit | edit source]
The deterioration of film-based photographic materials, specifically those made from cellulose nitrate, cellulose acetate, and polyester, varies due to their chemical compositions and environmental sensitivities. Each type of film has distinct stability issues and deterioration paths, influenced by the inherent properties of the material and the storage conditions.[edit | edit source]
Deterioration of Cellulose Nitrate[edit | edit source]
Cellulose nitrate film, historically used across various formats, is highly unstable chemically. This instability manifests as autocatalytic degradation where nitrate groups break off, forming nitric acid in the presence of moisture, accelerating the decay process. Common signs include yellowing of the film, stickiness, strong nitric acid odor, and eventual disintegration into a powdery substance. The degradation can catalyze further deterioration in nearby materials, particularly other film types. Notably, degraded cellulose nitrate poses severe fire risks as it can ignite at temperatures as low as 41°C, with the ability to burn rapidly, producing toxic gases.[edit | edit source]
Deterioration of Cellulose Acetate[edit | edit source]
Known as "safety film" due to its non-flammability compared to cellulose nitrate, cellulose acetate still suffers from significant stability issues, commonly referred to as "vinegar syndrome." This deterioration results from the hydrolysis of acetyl groups in the cellulose acetate, leading to the formation of acetic acid, which imparts a strong vinegar smell. The film becomes brittle, shrinks, and may exhibit channeling, curling, and bubbling of the emulsion. The deterioration accelerates in high-humidity environments and can lead to the emission of acids that may further degrade other materials stored alongside it.[edit | edit source]
Deterioration of Polyester[edit | edit source]
Polyester film bases, such as polyethylene terephthalate, are known for their exceptional chemical and dimensional stability. They resist most common forms of chemical degradation and do not exhibit the same rate of deterioration as nitrate or acetate films. The primary concerns with polyester are physical damage and the potential for adhesive failures during splicing, as polyester is highly tear-resistant. This resilience makes polyester an ideal choice for applications requiring long-term stability, such as archival film and important photographic works. However, challenges include its slick surface, which initially hindered emulsion adhesion, and its strength, which can cause damage to equipment during jams.[edit | edit source]
Conservation[edit | edit source]
Surface Cleaning[edit | edit source]
Dust and accretions on negatives can be removed using low-intervention methods, though care is needed to avoid scratching, especially on degraded emulsion.
Dusting can be done using compressed air tools like bulb blowers or gas dusters, and physical contact should be minimized to avoid damaging the emulsion.
Grease or fingerprints, which are particularly harmful, can be cleaned with specialized solvents in well-ventilated areas and using protective gear. This should be done cautiously to prevent damage, especially in areas with retouching media.
Conservator Interventions[edit | edit source]
Tenacious particulates may require gentle brushing with soft bristle brushes or micro-fibre cloths. Anti-static tools can help in managing dust buildup.
Solvent cleaning should be approached with caution, using appropriate solvents and materials to avoid damaging the negatives.
Water-based cleaning methods are generally not recommended unless by a trained conservator due to the high risk of emulsion damage.
Emulsion Separation[edit | edit source]
In cases where the plastic film base deteriorates, the emulsion may need to be separated to preserve the image. This process, known as stripping, is intricate and typically reserved for highly valuable items. The separated emulsion (pellicle) is chemically stable and can be scanned and stored appropriately if physical recovery is feasible[2].
Housing and Storage Considerations[edit | edit source]
Housing[edit | edit source]
All negative enclosures must pass the Photographic Activity Test as per ANSI Standard IT 9.2-1991. Before housing, negatives should be dusted with a wide, soft brush.
Enclosures should be labeled with permanent, archival ink complying with ANSI Standard IT 9.2-1991, with labels placed away from the emulsion side of the negatives.
Handling procedures differ based on the condition of the negatives; use nitrile gloves for negatives in good condition, and neoprene gloves, goggles, and a respirator for seriously deteriorated negatives.
Deteriorated negatives should be isolated and stored individually in paper envelopes avoiding glue seams next to the emulsion. These materials should also comply with ANSI Standard IT 9.2-1991.
Negatives should be stored snugly in reinforced, acid-free boxes with high alpha-cellulose content, fitting tightly with clam-shell type lids, and should not mix different formats or film types.
Sheet film should be stored flat in drop-front boxes unless they show severe deformations and brittleness, in which case they should be stored vertically. Information from original acidic boxes should be transferred to acid-free, buffered paper and stored separately or discarded.
Special precautions for nitrate materials include isolation to prevent acidic gas emissions, notification to fire services due to flammability, and replacement in general storage with acid-free separation sheets indicating new locations.
Rehousing should be in new buffered paper four-flap envelopes or L-weld sleeves that meet ANSI IT9.2 specifications, placed within archival boxes in Ziplock bags in frost-free freezers with a humidity indicator inside. Perforated film cans should be used for nitrate motion picture film to allow gas escape.
Ensure all old information is transferred to the new housing and seek immediate funding for duplication programs to preserve content.
Temperature and Humidity Control[edit | edit source]
The longevity of cellulose nitrate and cellulose acetate film bases can be significantly extended by controlling environmental factors. Research indicates that humidity control can improve film longevity by three to four times, while temperature control offers even more substantial benefits, especially when combined with low humidity. High temperatures and relative humidity (RH) levels accelerate the deterioration process of these materials, whereas lower temperatures and RH levels are crucial for their long-term preservation.
Polyester film, due to its high chemical stability, requires less stringent temperature and RH controls, though it is still necessary to protect the image silver from oxidation.
Legal and Safety Standards for Storage[edit | edit source]
Cellulose nitrate film, known for its high flammability, is subject to strict legal storage standards. NFPA 40 is the primary standard for storing cellulose nitrate film and is widely adopted internationally, although local regulations can vary its implementation and interpretation. Storage requirements stipulate that quantities exceeding 11 kg (25 lbs) must adhere to NFPA 40 standards, while smaller quantities should still be segregated and handled with care similar to other plastic films.
International Standards and Recommendations[edit | edit source]
Environmental standards for the preservation of photographic materials have been established by entities like the International Organization for Standardization (ISO). These include ISO 18934:2011, which pertains to the storage environment for multiple media archives, and ISO 18911:2010, which focuses on storage practices for processed safety photographic films (ISO 18911:2010 Imaging materials — Processed safety photographic films — Storage practices) and ISO 18928:2013 Imaging materials — Unprocessed photographic films and papers — Storage practices.
Contemporary guidelines suggest maintaining specific temperature and humidity set points to prolong the life of photographic collections, especially those prone to vinegar syndrome and other forms of deterioration. While earlier recommendations from ANSI in 1985 suggested that 18°C and 25% RH were adequate for storing cellulose acetate film, practical experiences have demonstrated that these conditions might not prevent the progression of vinegar syndrome.
The recent adjustments in museum and archive environmental standards have allowed for greater flexibility and cost savings. However, stringent environmental controls remain necessary for storing materials like cellulose nitrate and cellulose acetate, particularly if deterioration has already begun.
Cold Storage[edit | edit source]
Cold storage significantly benefits all photographic materials, including black and white and color prints and negatives. It is particularly crucial for materials like cellulose nitrate and cellulose acetate due to their chemical instability. Research supports that lower temperature storage greatly enhances the longevity of these materials. Humidity-controlled, sub-zero temperature storage can slowichemical activity and degradation to a minimal level. This is especially vital for deteriorating plastic film bases. Though costly, cool, cold, and sub-zero storage environments can be adapted to collection size, with more economical options available for smaller collections[3].
Proper acclimatization is essential when removing negatives from cold storage to prevent condensation and potential water damage. Negatives should be warmed gradually to ambient temperature while still wrapped to avoid any moisture condensation.
Managing humidity is critical as photographic materials, particularly gelatin, are highly hygroscopic and can absorb moisture, leading to physical and chemical degradation. The equilibrium moisture content (EMC) of photographs should be managed by adjusting relative humidity (RH) in conjunction with temperature changes to maintain the stability of photographic gelatin and prevent it from becoming too soft or brittle.
Monitoring the condition of collections is crucial to detect early signs of deterioration, such as acidity levels indicated by specific odors from degrading film bases. Techniques include the use of acid indicator strips (A-D Strips) to monitor "vinegar syndrome" in cellulose acetate films and regular surveys to assess the physical state of the negatives.
By focusing on controlled storage environments and proactive monitoring, institutions can effectively manage the preservation needs of photographic materials, especially those susceptible to rapid deterioration like cellulose nitrate and acetate films.
Emergency Recovery[edit | edit source]
Keep wet material submerged until it can be professionally rinsed in distilled water and dried.
Prepare a receiving area before moving items.
Maintain wetness by packing in containers lined with plastic bags and adding distilled water.
Separate any dry material from the wet materials.
Handle with plastic gloves and avoid touching the image area.
Deteriorated acetate should be frozen or air-dried quickly due to a low recovery rate. For air drying, lay negatives flat with the emulsion side up on polyester web over absorbent paper, changing the paper as needed. If the negative is only slightly deteriorated, it may be hung to dry on clotheslines using plastic or rustproof clips, ensuring the objects do not touch.
References[edit | edit source]
- ↑ "Completing the Polarization Test" provides instructions for creating a film viewer are available via the National Parks Service (https://www.nps.gov/museum/coldstorage/pdf/2.3.1b.pdf).
- ↑ Munson, Doug. 1997. The Pellicular Burlesque. Topics in Photographic Preservation, Volume 7. p. 55-65. Available at: https://resources.culturalheritage.org/pmgtopics/1997-volume-seven/07_08_Munson.pdf
- ↑ NPS. 2009. Conserv-O-Gram 14/12: Cold Storage for Photograph Collections – Vapor-Proof Packaging. Available at: https://www.nps.gov/museum/publications/conserveogram/14-12.pdf
Further Reading[edit | edit source]
- Adelstein, Peter Z. 1989. "History and Properties of Film Supports." Proceedings of Conservation in Archives, International Symposium Postprints. Ottawa, Canada: 89-101
- Fisher, Monique. 2020. "5.1. A Short Guide to Film Base Photographic Materials: Identification, Care, and Duplication." Northeast Document Conservation Center Preservation Leaflet, Andover, Mass. https://www.nedcc.org/free-resources/preservation-leaflets/5.-photographs/5.1-a-short-guide-to-film-base-photographic-materials-identification,-care,-and-duplication
- P. Z. Adelstein, J.-L. Bigourdan & J. M. Reilly. 1997. "Moisture Relationships of Photographic Film." Journal of the American Institute for Conservation, 36:3, 193-206, DOI: 10.1179/019713697806124475
- Hill, Greg. Care of Plastic Film-based Negative Collections – Technical Bulletin 35. Available at: https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/technical-bulletins/care-plastic-negative.html#a3
- Horvath, David. The Acetate Negative Survey. 1987. Available at:https://gawainweaver.com/images/uploads/Horvath_AcetateNegativeSurvey.pdf
- Messier, Paul. Preserving Your Collection of Film-Based Photographic Negatives. Available at: https://cool.culturalheritage.org/byauth/messier/negrmcc.html
- McCabe, Constance. 1991. "Preservation of 19th-Century Negatives in the National Archives." Journal of the American Institute for Conservation, 30:1, 41-73, DOI: 10.1179/019713691806373213
- National Parks Service. No Date. Completing the Polarization Test. https://www.nps.gov/museum/coldstorage/pdf/2.3.1b.pdf
- Valverde, Maria Fernanda. 2005. "Photographic Negatives: Nature and Evolution of Processes, 2nd Edition." Advanced Residency Program in Photographic Conservation, George Eastman House, Image Permanence Institute. https://s3.cad.rit.edu/ipi-assets/publications/negatives_poster_booklet.pdf
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