IFLA Core Programme
Preservation and Conservation
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 photographic images.
Deteriorated photographs of extreme artifactual value may require specialized conservation treatment by a professional photograph conservator, often a costly, skill-demanding, and time-consuming procedure. For the majority of photographs in research collections, single-item conservation of deteriorated photographs is probably not a feasible or a cost-effective preservation solution. Instead, promoting proper care, handling, and storage through staff and user education will have a more lasting, positive impact on the preservation of a collection.
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 gelatin prints, glass plate and film base negatives, and color transparencies.
Photographs are composite objects. A typical photograph consists of three different parts:
Many different final image materials and binders have been used over the years. Today, however, almost all black-and-white photographs are composed of silver suspended in gelatin.
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 differ with types of photographic materials. Photographs made by processes that may offgas and damage other materials must be stored separately. The ability to identify photographic processes is also a prerequisite for selecting appropriate 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 historic photographic processes are available.
Salted paper prints
Glass plate negatives (general)
Collodion wet plate glass negatives
Gelatin dry plate glass negatives
Nitrate negatives (introduced by Kodak; ceased production in 1951; dates of production outside the United States vary)
Gelatin and collodion printed-out photographic prints
Black-and-white gelatin developed-out photographic prints
Acetate negatives introduced for sheet film
Chromogenic color film and transparencies (introduced by Kodak; Kodachrome was the first process)
Instant black-and-white process (introduced by Polaroid; sepia first, then black-and-white in 1950)
Polyester film introduced
Instant color print process (introduced by Polaroid; Polacolor was the first process; SX 70 was introduced in 1972 and Polacolor 2 in 1975)
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, dating it, and assigning an accession number.
Materials in the collection, as well as all incoming materials, should be screened systematically during the inventory and appraisal steps in order to identify items with special preservation problems that require conservation treatment or stabilization until treatment can be obtained. Such actions may include protective boxing or stiff card supports underneath brittle or broken photographs. The main problems to look for are: (a) inherent problems affecting the structure of the print, such as extreme fragility, flaking binder layers, or other physical damage; and (b) external problems, such as active mold, insect infestation, or the use of inappropriate pressure- sensitive tape or rubber cement adhesives.
Catalog records should be prepared for each item in the collection that state the nature of the object, its physical description, and an evaluation of its condition. Where large numbers of similar materials are concerned, a finding list containing general or characteristic information may suffice in lieu of individual item records. Cataloging and access tools can support preservation by minimizing the need for researchers to handle original photographs or one-of-a-kind images, including negatives for which no reference copy exists. If good cataloging and finding aids are provided, the need for researchers to browse through originals is reduced. Some examples of finding aids that promote access to images (but not to originals) are: (a) a small 35mm photo duplicate contact print of the original attached to a catalog card; (b) photographic images stored on videodisk; (c) photographs reproduced on microfilm or microfiche; and (d) photocopies of originals.
Once the collection has been inventoried, appraised, cataloged, and arranged to library and archives standards, each photographic medium--prints, film base and glass plate negatives, and slides--should be housed and stored separately if possible. Items that are too deteriorated to be handled without damage should be duplicated. A photocopy can be made from the duplicate for research purposes. Once a deteriorated original is duplicated it may be withdrawn from service to researchers.
Comprehensive collection management includes proper maintenance of and storage for the collection. Protective housings (to be discussed later) can minimize handling damage and wear and tear. A proper storage environment is the best defense against deterioration, since photographic processes are affected by harmful chemical gases, high temperature, and improper relative humidity levels.
Four principal factors contribute to photographic deterioration: poor environmental storage conditions, the presence of residual photographic processing chemicals or the use of exhausted processing chemicals, poor storage enclosures and shelving conditions, and rough or inappropriate handling that results in unnecessary wear and tear.
The environmental factors that affect the preservation of photographic materials are relative humidity and temperature, air pollution, light, and housekeeping practices.
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.
High temperature speeds up the rate of deterioration. The higher the temperature, the faster a photograph deteriorates, especially at high RH levels. High humidity and temperature, combined with the damaging effects of air pollution, are especially damaging and cause silver images to oxidize and color dyes to shift and fade.
High temperature and high humidity conditions may contribute to the growth of microscopic mold spores on the image-containing layer and on primary and secondary paper supports. Once active mold infests photographic materials it is usually impossible to remove without damaging the photograph. Mold tends to develop when the temperature is above 75-80° F and the RH is greater than 60%.
Temperature and RH fluctuations, or "cycling", result in chemical and mechanical changes that are especially damaging to photographs. Cycling promotes the movement of moisture in and out of a photograph, speeds up the rate of chemical deterioration of primary and secondary supports, and promotes the breakdown of the binder that holds the final image material to the support. When both humidity and temperature are high, or when materials undergo temperature and RH cycling, structural damage and the rate of chemical deterioration are greatest.
The ideal RH for storage of a mixed collection containing historical photographic prints, slides, and negatives is between 30% and 50% without cycling more than 5% a day. If only photographs are stored in a given area, 30-40% RH is best. If photographs are stored with paper, parchment, or leather materials, it may be necessary to maintain 40-50% RH to avoid placing unwanted stress on non-photographic materials. However, some materials, such as negative films and transparency films (nitrate and acetate plastic) and some historic glass plate negatives, will deteriorate further at 40-50% RH. The deterioration of acetate and nitrate is strongly dependent on RH even at moderate levels of 40-50%. Recent American National Standards Institute (ANSI) specifications recommend 20-30% RH for long-term storage of "safety" film (acetate and polyester base) to assure maximum life expectancy. Recent research (Reilly, 1991) indicates that historic nitrate film also benefits from these same storage conditions. Glass plate negatives should be stored at 30-35% RH to minimize glass decomposition and flaking (McCabe, 1991).
Storage temperatures should be kept as low as possible but high enough to allow reasonably comfortable working conditions for staff. The highest recommended storage temperature for black- and-white negatives and prints is between 65° and 70° F. Daily fluctuations greater than 5° should be avoided. Color materials, which fade more in elevated temperatures, should be kept in cool storage whenever possible (a set point within the range of 40-65° is best), or in cold storage (25-40° F) whenever feasible. Generally, the colder the storage the better. When choosing a system, keep in mind that cold storage units are expensive to maintain, especially units for lower temperatures. Refrigerators may present low cost options for small, valuable collections of color materials (Wilhelm, 1990). Caution must be exercised if using cold storage systems to avoid elevated RH or water condensation on valuable original photographs. All cool or cold storage systems limit access to the collections because the photographs must equilibrate to ambient temperature and RH before they are used in order to avoid moisture condensation.
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. Oxidant gases cause photographic images to fade by chemically interacting with the silver image material.
Particulate matter, such as soot and ash particles from manufacturing processes, exists in abundance outdoors and can enter the library or archives through heating and cooling ducts, doors, and windows. Particulates, which may be greasy, abrasive, and chemically or biologically active, settle on shelves and on collection materials and create dust that is spread to other materials when they are handled.
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 acid. These acids attack all components of photographs and cause silver images to fade and paper and board supports to 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 gaseous and particulate matter. A well-designed filtration system includes cellulose or fiberglass filters that remove particulate matter, and a charcoal 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 gases. Many photocopiers 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 the silver image material causing it to fade. Use only mild solvents such as soaps and water-based latex paints in a well-ventilated area to clean and 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.
Well-processed black-and-white silver gelatin prints and negatives are essentially stable to moderate amounts of light. Primary and secondary supports can be seriously damaged, however, when exposed for extended periods to visible light in the 400- to 500-nanometer range, and to ultraviolet (UV) light in the 300- to 400-nanometer (near ultraviolet) region. Damage caused by light is cumulative and depends on the intensity and length of exposure. Sunlight and standard fluorescent light are both strong sources of UV. Color slides are particularly susceptible to fading when exposed to both visible and UV light. For example, Kodachrome slides can fade significantly within 10 minutes of projection, although Kodachrome has excellent color stability in dark storage.
Historic photographs and color photographs should be kept at lower light levels than modern black-and-white photographs. Light levels in exhibits should be kept as low as possible, but high enough to allow patron viewing. Levels for historic and color photographs should be in the range of 3-10 footcandles (30- 100 LUX). Although some modern photographs can be exhibited under much brighter conditions (up to 20 footcandles), it is best not to exceed 10 footcandles whenever possible. Ultraviolet light levels should not exceed 75 microwatts per lumen. A UV meter is required to measure ultraviolet light levels; incandescent light levels can be measured with a photometer or even a camera light meter (Canadian Conservation Institute, Notes).
Reading room lights should be kept at a comfortable viewing level. Windows and fluorescent lights in reading rooms and storage areas are often chief sources of damaging ultraviolet light. The installation of low-UV-emitting bulbs or UV-absorbing fluorescent bulb sleeves can help eliminate this problem. Window glazing or the installation of window shades may also help. Low- UV-emitting bulbs and sleeves are available from several manufacturers. Light levels in storage areas can also be controlled by the use of timed shut-off switches. Dark cloths or sheets of folder stock (heavyweight paper) or mat board should be available in reading rooms for covering objects when not in use by readers. Photographs should be covered if they are not immediately returned to storage after use.
Insects (silverfish, cockroaches, beetles) and rodents (rats, mice, and squirrels) are all attracted to photographic materials. In addition to eating materials, they also foul the storage area and materials with their droppings. They make nests that can be difficult to locate and remove. A good policy is to prohibit eating or drinking where collections are stored. Floors, shelves, boxes, and cabinets should be dusted or vacuumed, or both, on a regular basis. Avoid storing collection materials on the floor where they are more likely to be damaged by insects and rodents or water leaks.
Major silver deterioration occurs when photographs are not correctly processed and washed, that is, when exhausted fixer is used or when photographs are not fixed for a sufficient time, or when washing is inadequate. Improper washing fails to rinse residual thiosulfate complexes (fixer) from the film or paper. Residual fixer left in the photograph reacts over time and causes the image, binder, and support to turn yellow or brown and the silver image to fade. High temperature and humidity speed this process. Photographs that were not well fixed remain light sensitive and may darken when exposed to light. Damage from residual chemicals occurs with time and can go unnoticed for years. To prevent this type of damage insist that all photographic chemical processing and development be done to ANSI standards, especially when duplicating negatives, making reference prints from collection negatives, and if feasible, when acquiring new photographs from photographers.
Proper storage for photographic materials is an important preventive measure that stabilizes delicate or fragile materials and provides basic care for all materials in the collection. Storage cabinetry and enclosures must be chosen and used carefully, however, so that they do not contribute to the deterioration of collection materials. Photographic materials can be seriously damaged if stored in cabinets made of inferior materials that offgas harmful chemicals or that do not provide adequate physical protection. Damage is also caused when photographs are stored loosely in oversized containers or too tightly in overstuffed drawers. Prints stored loosely in a file drawer will slump and curl, for example, and be vulnerable to damage each time the drawer is opened and items are handled. Glass plate negatives are especially fragile and will break when crowded into file cabinets unprotected or stacked on top of one another.
Storage furniture, including cabinets and shelves, should be made of non-combustible, non-corrosive materials such as stainless steel, anodized aluminum, or steel with a powder-coated finish. Shelves made of wood and wood by-products should generally be avoided since they contain lignin, peroxides, and oils that can offgas or migrate to photographic materials. New baked enamel shelving units may offgas harmful chemicals if not properly cured during manufacture.
Prints, negatives, and slides can be damaged by enclosures that are poorly designed or are made of inferior materials. Acidic chemical agents from poor quality materials can migrate to photographs and destroy the images they were meant to protect. Poorly designed enclosures can produce the same result.
Many commercially available enclosures are labeled "archival" or "acid-free". However, some of these same items may contain lignin, dyes, sizing agents, coatings, plasticizers, or other harmful additives. Never use enclosures made from unprocessed woodpulp paper, glassine, or polyvinyl chloride (PVC) to house or store photographs. Avoid products made from colored papers because they often contain dyes or inks that are unstable and will migrate or bleed onto photographs or otherwise adversely affect the photographs stored within. For an enclosure material to be completely safe it must meet or exceed the specifications in ANSI standard IT9.2-1991 (or the latest revision) including the Photographic Activity Test (PAT). Purchase enclosure materials from a reputable supplier.
Paper envelopes are often used to store prints and negatives. Adhesives used to seal envelopes may cause staining and fading of the silver image. Thus, the emulsion (or image) side of a print or negative should be placed away from the seam so that staining or fading of the front is less likely. When envelopes with seams are used, the seams should run along the sides of the envelope rather than down the center. A good approach to housing photographs is to provide several layers of protection by first placing photographs into sleeves or envelopes, then into folders, and finally into document storage boxes. This procedure may not be feasible in every institution or with every type of collection. In some cases, grouping photographs into folders and then into storage boxes may suffice.
The choice between paper or plastic enclosures should be based on the type of photographs to be housed and their condition, the anticipated amount of use the materials will receive, financial resources, and environmental storage conditions. Paper enclosures usually cost less than plastic, but items that are used frequently can be abraded by repeated removal from and insertion into paper enclosures. Paper sleeves and envelopes should be made according to ANSI specifications, which recommend that the paper have an alpha cellulose content of 87% and contain no lignin, groundwood, or alum-rosin sizing. The paper should be buffered to a pH of 7-8.5. Unbuffered paper (tending to have a pH of 6-7) may be preferable for some processes such as cyanotypes. Buffered paper is preferred for acetate and nitrate films, platinum prints, and prints mounted on acidic boards.
Plastic enclosures are preferred for frequently used collections because they protect photographs from finger prints and provide physical support. Plastic enclosures should be made from an inert plastic such as polyester, polyethylene, or polypropylene. These plastics are generally considered non-damaging and may be used safely with many photographic materials. Avoid all plastics that have fillers, coatings, or UV absorbers. Avoid the use of polyester, polyethylene, and polypropylene that has a hazy film on the surface, which indicates that the plastic film is coated or is heavily plasticized. Avoid using adhesives or fasteners that may cause chemical or physical damage, such as rubber cement, pressure-sensitive tape, paper clips, or rubber bands. Plastic enclosures should not be used with nitrate or early acetate films.
PRINTS. An ideal storage method for artifactually valuable photographs is to place the print inside a polyester "L" sleeve with a piece of 2-ply board behind the print for added support. A polyester "L" sleeve is made from two pieces of polyester placed on top of one another and joined along two adjacent edges. Place the sleeved photograph into a buffered pH folder and into a document box. Prints larger than 11 by 14 inches should be shelved horizontally. If vertical storage is chosen, be sure the box is snugly filled, or use a spacer to fill unused space to prevent photographs in the box from slumping. If vertical shelving is chosen, make certain the document box is well supported on the shelf. A less costly approach for large collections or collections that receive little use is to place the photograph into an "L" sleeve or a folder and use the 2-ply support only for brittle items.
OVERSIZED PRINTS. Place oversized prints in a folder, interleave with paper, or sleeve in polyester as above. The housed photographs should then be stored in a large document box on shelves or in map storage drawers. Rolling should be avoided since the photograph may crack when it is unrolled for use.
FRAMED PHOTOS. Remove the photograph from the frame and store as above. If framed storage is available, the framed photographs should be protected from light exposure with dark cloth coverings. If the photograph is stored framed, check that the matting is appropriate and of high quality materials.
GLASS PLATE NEGATIVES. Intact glass plates may be stored individually, in seamed or seamless paper enclosures. The plates should then be arranged vertically on their long edges in document storage boxes, which can then be stored on open shelving or in cabinets. Seamless sleeves are best for low-use negatives, such as those that have been retired from darkroom use. Shelving with adequate strength is needed to hold the weight of the boxed glass plate negatives. Boxes should be clearly labeled "fragile/glass" and "heavy". Filler 2-ply board or corrugated board should be used to fill out partially filled boxes to minimize jostling of plates during handling. Plates larger than 5 by 7 inches are ideally stored in cabinets with rigid metal dividers spaced every 1 to 1 1/2 inches. Plates should always be placed on their long edge for vertical storage.
BROKEN GLASS PLATES, OR THOSE WITH DETERIORATED IMAGE LAYERS. Damaged plates should be stored in sink mats constructed to guidelines suggested by McCabe (1991) with materials that meet the ANSI PAT test. Cracked plates should be supported with a piece of glass or lignin-free ragboard until they can be duplicated, safely sink matted, or examined by a professional conservator. The storage and stabilization of damaged glass plate negatives should be done with the consultation of a conservator.
NITRATE NEGATIVES. Cellulose nitrate film was manufactured between 1889 and 1951 in the United States. It was produced into the 1960s in other countries. Kodak was the first to manufacture nitrate film, but it was manufactured by other companies worldwide. Nitrate film is inherently unstable and becomes acidic, sticky, and brittle with age. In large quantities nitrate film can also be a fire hazard, although this risk pertains more to motion picture film than to still photographs stored in individual paper enclosures. Nitrate deteriorates in stages, beginning with a breakdown of the cellulose nitrate plastic support. As nitrate deteriorates it poses a threat to other types of photographs stored in the area by emitting oxides of nitrogen, which attack the silver image, the gelatin binder, and eventually the support base of other papers and films. Nitrate materials should be identified, accurately duplicated, housed in buffered paper enclosures (never plastic), and stored away from other collection materials in a well-ventilated room. Fire codes may require that the nitrate materials be stored separately in fireproof cabinets, or in vaults, or completely off-premises. Storage at low temperature and low RH greatly slows the deterioration of nitrate film.
CELLULOSE ACETATE NEGATIVES. Starting in the 1930s cellulose nitrate base film was gradually replaced by "safety film" or cellulose acetate films (diacetate, triacetate, acetate propionate, acetate butyrate). All cellulose ester films, including diacetate and triacetate, tend to shrink when plasticizers and solvents introduced during manufacturing evaporate out over time and cause the film base and the gelatin emulsion to cockle and distort. When this happens, the emulsion layer wrinkles and delaminates from the film base support. Eventually the image is distorted by the network of wrinkles or channels formed in the emulsion layer. In addition, the film base becomes increasingly acidic and decomposes. The smell of acetic acid is a sign that the cellulose acetate film base itself is deteriorating and that damage is occurring. Triacetate film, introduced in 1948, is the most stable of the acetate films and is in wide use today. All acetate films should be inspected periodically for signs of deterioration. Deteriorated items should be duplicated before damage worsens and should be stored in buffered paper sleeves, under very stable environmental conditions, while awaiting duplication. Unstable, early acetate negatives should be stored separately from prints in a well- ventilated storage room. Plastic enclosures may be used for recently produced safety film negatives (acetate or polyester) that are expected to receive use. Storage at low temperature and low RH greatly slows the deterioration of acetate film.
COLOR TRANSPARENCIES. Virtually all color processes are inherently unstable because the final image material consists of organic dyes rather than silver or pigment particles suspended in gelatin. Of the many color processes commercially available, the Cibachrome process is the most stable. Exposure to light will cause most color dyes to fade, but some color dyes will also fade in the dark. In general, high temperatures speed the rate of color fading. Color slides should be housed in suitable plastic sleeves or lignin-free slide storage boxes. Color separations of deteriorated color materials can be made that preserve in silver the three dye layers of the original color image. This, however, is a costly process and may not be feasible for institutions with many color slides. An alternative is to place slides in cold storage (25-40 deg F and 20-40% RH), which will slow color fading and image loss.
ALBUMS, SCRAPBOOKS, AND MOUNTED PHOTOGRAPHS. Historical print mountings were often made of acidic, unstable materials. Many over-the-counter adhesives used to mount photographs into albums and scrapbooks are acidic and will eventually discolor, become brittle, and damage materials. When acidic paper mounts become brittle, the photographic image itself is at risk because of breakage. Mounted photographs that are fragile or brittle may be stabilized with a rigid support such as 4-ply matboard inside a protective enclosure or by placement into a sink mat for protection.
Albums can be wrapped in paper and placed in a document box or in a fitted protective enclosure. On rare occasions albums may be given full conservation treatment, especially if they are particularly valuable. However, this should be the exception rather than the rule. Heavily used albums or scrapbooks should be photographically reproduced. Interleaving should be done judiciously because it adds bulk to an album and places undesirable stress on the binding. Examples where album pages may benefit from the protection provided by interleaving include the following: photographs that are glossy or easily abraded, or both; photographs that have fixer stains; platinum prints; and photographs with tape or adhesive applied in such a way that it may come in contact with other items in the album.
The risk of damage to materials is increased when researchers and staff who are responsible for photographic materials are not trained in the proper care and handling of those materials. Ignorance, neglect, and carelessness account for a significant percentage of damage to photographs. Repair of photos with pressure-sensitive tape, marking original prints with ink or felt-tip pens, and exhibition of materials under inappropriate conditions are examples of negligence. Neglect also includes the lack of a disaster response plan, inadequate security precautions, and poor collection management procedures that require valuable originals to be handled repeatedly. Carelessness includes rough handling during cataloging, housing, and viewing; and damage to materials as a result of inadequate transport systems.
When handling photographs and negatives, be sure that hands are freshly washed, wear clean lint-free cotton gloves, and avoid touching the photograph surface. If a photograph must be moved a short distance or turned over during examination, use an auxiliary support (such as a piece of Plexiglas, 2- or 4-ply rag board, or folder stock) to protect the item from damage caused by unnecessary bending and flexing. Use a stable, appropriately sized book cart with horizontal shelves to transfer materials between storage and research areas. Provide book cradles in research areas that allow photograph albums to be viewed safely. Cradles permit a tightly bound book to be opened enough to be read but not so far that it is damaged. Felt covered "snakes" filled with sand can be used to hold pages open as long as they do not touch the surface of photographic materials.
Avoid projecting a color slide longer than ten seconds because the intense projector light causes color dye shift and fading. Slides made for frequent projector use should be on Ektachrome film, which is less prone to color fading under intense projection light. However, Ektachrome is more prone to fading in dark storage than Kodachrome slides. Thus Kodachrome is the preferred slide material if it is not subjected to frequent projection. Recent research suggests that Fujichrome is a good compromise for frequently used slides (Wilhelm, 1990).
Train staff to arrange, describe, and rehouse newly acquired materials with care. Instruct them in the proper method for handling films, glass plates, and prints, as well as brittle, broken, or flaking photographs of all types. Provide adequate storage enclosures and other necessary supplies during housing and cataloging so that materials will be housed properly. Evaluate training procedures on a regular basis and revise them as needed.References
Canadian Conservation Institute. Using a Camera to Measure Light Levels. Notes 2/5.
McCabe, Constance. Preservation of 19th Century Negatives at the National Archives. Journal of the American Institute for Conservation 30, no. 1: 41-73 (Spring 1991).
Reilly, James M., Peter Z. Adelstein, and Douglas W. Nishimura. Preservation of Safety Film. Final Report to the Office of Preservation and Access. National Endowment for the Humanities (Grant no. PS-20159-88). March 1991.
Wilhelm, Henry. Going, going, gone. Popular Photography 97: 6 (1990).
This project was made possible in part by the International Federation of Library Associations and Institutions (IFLA) and the Council on Library Resources. The author is particularly indebted to all those who reviewed and commented on draft versions of this document, including Constance McCabe, Debbie Hess Norris, and Mary Lynn Ritzenthaler. Special thanks in particular go to Sarah Wagner (Technical Editor), Carrie Beyer (Production Manager), and Merrily Smith (Managing Editor). In addition, the author would like to thank the Library of Congress, the National Archives and Records Administration, and the University of Delaware.Mark Roosa
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