NARA recommends buffered paper stock for the storage of all photographic materials. The degradation of all paper products over time means that the use of non-buffered, neutral paper stock results in short order in an acidic folder that becomes increasingly acidic. Recent research has shown that the only hazard to alkaline-sensitive photographs is in the event of prolonged exposure to water. Since buffered paper has been shown over time to drop in pH, this is only an issue for the first 10 years or so of the package's lifetime, after which the enclosure is neutral pH or slightly acidic.
A photographic image is formed through the exposure of a photosensitive emulsion to light: this is the essence of a photograph. Photo emulsion, which is carried on a paper or plastic support, is composed of a light-sensitive image material (e.g. silver particles) dispersed in a binder substance (e.g. gelatin). Most prints are typically positive images. Photo prints may be full-color or monochrome, which means that the image is rendered using a single color (e.g. B&W prints). Monochrome prints are split into three categories: 1-layer (image material only), 2-layer (image material in a binder), or 3-layer (image material in a binder atop a baryta coating).
Photo emulsion is composed of a light-sensitive image material (e.g. silver particles) dispersed in a binder substance (e.g. gelatin). The emulsion is carried on a paper or sometimes a plastic support. Monochrome photographic prints are split into the following three categories popularized by James Reilly: 1-layer (image material only), 2-layer (image material in a binder), or 3-layer (image material in a binder atop a baryta coating).
When we talk about the binder layer, we are talking about the layer that suspends the photographically sensitive material. In the case of silver gelatin processes, gelatin binds the evenly-dispersed silver particle image into what is in total called the emulsion.
Photographic materials have complex physical and chemical structures that present special preservation challenges to the librarian and archivist. Since the birth of photography in the late 1830s, many different photographic processes and materials have been utilized, each subject to deterioration through time and with use. Although deterioration is an ongoing natural process, nevertheless much can be done to slow the rate at which it takes place in photographs.
This publication is intended to provide a basic understanding of how and why photographs deteriorate and what can be done to slow this process. The information below focuses on the photographic formats most commonly found in research libraries and archives, namely black-and-white silver prints, glass plate and film base negatives, color chromogenic dye photographs (including negatives, prints, and transparencies), and digital output or hardcopy: ink jet prints, dye sublimation prints, and electrostatic prints.
Photographs are composite objects. Since the advent of photography, many different materials have been used to make a wide variety of photographic materials. A typical photograph consists of three different components:
Identification of various types of photographs requires a basic knowledge of the history of photographic processes. Curators and archivists charged with responsibility for photographic collections must be at least somewhat familiar with the various photographic processes and know when they were used. This information is needed not only for cataloging but also for making informed preservation decisions. Processes must be identified in order to distinguish between later copies and vintage originals. In addition, storage needs may differ with types of photographic materials. Photographs that are hazardous (such as cellulose nitrate), or may give off harmful gases as they deteriorate (such as nitrate and acetate negatives), or damage other materials (such as nitrate, acetate, and diazo) must be stored separately. The ability to identify photographic processes is also a prerequisite for selecting appropriate storage environments and storage enclosures for photographs. For example, acetate and nitrate film negatives should be stored in individual buffered paper sleeves because plastic enclosures trap harmful offgassing from the film base, which further accelerates deterioration of the image and film. Many excellent books devoted to photographic processes are available. (Coe and Booth 1983, Reilly, 1983, Jarry 1996, Juergens 1999)
Collection management includes four basic components: inventory, appraisal, cataloging, and proper housing and storage. Inventory is needed to determine which photographic processes are represented in the collection and which prints are mounted, unmounted, or in albums. Appraisal of the collection entails evaluation based on value, appropriateness of the collection to the mission of the institution, and an assessment of housing and preservation needs. Cataloging and arrangement involves identifying each item or collection, dating it, and assigning an accession number.
Once the collection has been inventoried, appraised, cataloged, and arranged to library and archives standards, certain photographic materials (such as cellulose nitrate and cellulose acetate film base materials, and chromogenic dye photographs) should be housed and stored separately if possible. By isolating these photographs, these items may be stored in colder and drier environments that will maximize their lifespan. In addition, segregation of some photographic materials, such as deteriorating film base materials, reduces the risk of damage caused by acidic offgasing that can damage other photographs stored nearby. Lastly, fire safety codes may require separate storage for cellulose nitrate materials. (NFPA 40) However the nature of many collections does not allow for separation of different materials and a compromise frequently must be made between the conflicting needs of the photographs in the collection. High-quality reproductions should be made for items that are too deteriorated to be handled without damage. Once a deteriorated original is duplicated or reproduced it may be withdrawn from service to researchers. Increasingly digitization projects are providing these types of surrogates.
Four principal factors contribute to the deterioration of photographs: poor environmental storage conditions, poor storage enclosures, rough or inappropriate handling that results in unnecessary wear and tear and shelving conditions, and in some cases, the presence of residual photographic processing chemicals or the use of exhausted processing chemicals.
Environmental Factors The environmental factors that affect the preservation of photographic materials are relative humidity and temperature, air pollution, light, and housekeeping practices. Relative Humidity and Temperature All photographic materials are sensitive to high, low, and fluctuating relative humidity (RH), which is a measure of how saturated the air is with moisture. High RH affects all components of photographs. High RH causes a gelatin binder to become soft and sticky, making it vulnerable to mechanical damage and image deterioration. Low RH causes the binder to shrink and crack and the secondary support to curl.
Air Pollution Air pollution attacks photographs in the form of: (1) oxidant gases, (2) particulate matter, (3) acidic and sulfiding gases, and (4) environmental fumes. Oxidant gases are composed primarily of pollution created by burning fossil fuels such as coal and oil. Nitrogen oxides (oxide and dioxide) and ozone are the two main gases that threaten photographic images. Nitrogen oxides are produced by combustion, as in automobile engines. Ozone occurs naturally in the upper atmosphere, but can be formed in the lower atmosphere when sunlight interacts with nitrogen oxide. Ozone is also produced by some electrostatic copiers and printers. Oxidant gases cause photographic images to fade by chemically interacting with the final image material. Silver photographs and some ink jet prints are both especially sensitive to pollutants.
The by-products of combustion combined with moisture in the atmosphere pose another risk to photographic materials. When fossil fuels such as coal and oil are burned, nitrogen and sulfur dioxide are produced. The reaction of nitrogen and sulfur dioxide with water in the atmosphere produces nitric and sulfuric acids. These acids attack all components of photographs and cause silver images to fade and paper and board supports to discolor and become brittle.
Environmental fumes can be especially damaging to photographic images even in small quantities. Peroxides from untreated wood, paints, and varnishes; poor quality paper or plastic products in close proximity to photos; and the fumes from common cleaning solvents can cause images to oxidize and fade.
Air entering the storage area should be filtered and purified to remove particulate and gaseous matter. A well-designed filtration system includes cellulose or fiberglass filters that remove particulate matter, and chemical absorption system that filters out gaseous pollutants. Air filters must be changed regularly to be effective. Air circulation should also be checked periodically. There should be no stagnant air pockets, or drafts that bring unfiltered outside air into storage areas. Storage cabinets, enclosures, and boxes may provide some protection from pollutants and harmful gases. Many photocopiers and printers emit ozone, which is damaging to photographs, so their use near collection storage areas should be avoided. Do not permit unsupervised cleaning or painting of storage areas. Do not allow unknown cleaning materials or those containing chlorine and other bleaches, oil- based paints, or varnishes to be stored or used near photographic materials. Avoid storing photographs in freshly painted rooms since paint vapors can interact with image materials causing them to fade. Detergents and soaps without chlorine are recommended for cleaning storage areas. Use only water-based latex paints to paint photographic storage areas. Ideally, latex-painted display cases or storage areas should be allowed to dry for at least a week before use with photographs. When ordering metal furniture, specify a powder-coated finish. 2b1af7f3a8