All plastic and paper materials used to house and store valuable and heirloom photographs should pass the Photographic Activity Test (PAT), a test to detect image fading resulting from harmful chemicals in enclosures and to detect staining reactions between enclosures and gelatin), as specified in ISO 14523: 1999. Refer to NEDCC Preservation Leaflet Storage Enclosures for Photographic Materials for a full discussion of the advantages and disadvantages of paper and plastic storage enclosures as well as an examination of pH buffered vs. unbuffered paper materials in housing photographic collections.
Photographic prints and negatives are best stored in individual enclosures. This reduces damage by giving the photograph or negative physical support and protection. Enclosures can be made of paper or plastic.
- protect from light and buildup of moisture and gases inside the enclosure;
- require more handling, as the object must be removed from the enclosure for examination; and,
- are cheaper and easier to write on than plastic enclosures.
- allow the user to view the image without handling it;
- can abrade the photograph during insertion and removal from the enclosure;
- can trap gases and moisture within the enclosure;
- can be difficult to write on and sometimes flimsy; and,
- usually have heat-sealed seams, which eliminate potential damage from adhesive seams.
There are several types of individual plastic enclosures, including L-Velopes (sealed on two adjacent sides); plastic folders that can be used within paper envelopes; and plastic sleeves that are open at two opposite ends, with a self-locking fold on one of the remaining sides. There are also a number of styles of ring-binder pages for prints and negatives.
In the past, conservators were concerned that certain photographic formats, such as color prints, cyanotypes, and albumen prints, could be damaged by the alkalinity in buffered enclosures. But recent research indicates that the pH level of enclosures is less important than their chemical makeup. Paper enclosures should pass the Photographic Activity Test (PAT), which determines whether the enclosures contain harmful chemicals that can cause image fading or staining.
If envelopes with adhesive seams are used, the adhesive must be stable, pH-neutral, and it must not react with silver; the seams should be on the sides or the bottom of the envelope; and the emulsion of the photograph should face away from the seams.
Once they have been individually enclosed in paper or plastic, photographs must be placed in archival-quality boxes. Where possible, items of similar size should be stored together; the mixing of different sizes can cause abrasion and breakage and can increase the risk of misplacing smaller items. Horizontal storage of photographs is usually preferable to vertical storage, since it provides overall support and avoids mechanical damage such as bending or slumping. The photographs should be stored flat in drop-front boxes of archival quality housed on shelves or in metal cabinets. All enclosures within a box should be the same size, fitting the size of the box. Acid-free, lignin-free file folders may be used to organize photographs within the box.
If necessary, vertical storage can be used. Small photographs of uniform size can be individually enclosed and placed vertically in boxes the same size as the photographs. Boxes of various sizes and types are available from conservation suppliers. For vertical storage in a filing cabinet, protected photographs should be placed in archival folders that are themselves placed in hanging file folders. Several photographs may be stored in each folder, and several folders may be placed in each hanging file. Lightly filled hanging file folders will prevent photographs from sliding down under each other in the drawer and will facilitate their handling. Alternatively, folders can be placed in archival document boxes, but the folders should not slump, and the photographs must be well supported.
Give special care to the storage of oversized photographic prints mounted on board or heavy paper. These supports are often acidic, causing the mounts to become brittle with age. Embrittlement of the board can endanger the image itself if the cardboard breaks in storage or during handling. Such prints should be placed in individual folders in archival-quality boxes of appropriate size and stored flat on shelves. Users and staff should be instructed to use these items with caution.
This category of media includes black and white or color negatives and slides, as well as more specialized formats like lantern slides, collodion wet and dry plate negatives, and silver gelatin wet and dry plate negatives.
Glass plate negatives and transparencies should be housed upright or vertically along their longest edge. Use four-flap envelopes or other housings that do not require the glass plate or transparency to make contact as it is removed and replaced into its enclosure. Padded boxes with slots or stiff dividers between the negatives and transparencies are best, and make sure the boxes are not too heavy. Label the boxes to indicate that the contents are heavy and fragile. Broken or cracked glass plates require special housings such as sink mats to prevent further damage. Do not allow two glass plates to touch together.
Oils and dirt from fingerprints can cause chemical damage to negatives and transparencies. Wear non-vinyl gloves (latex or nitrile) when handling negatives and transparencies. Cotton gloves can be slippery, especially when handling glass plates.
Handle glass plates as infrequently as possible, but when required be certain to hold them on opposite edges with both hands. Do not hold them by one edge or by the corners.
Exposure to light greatly accelerates the fading of the color dyes used in various types of film-based materials. Exposure to strong sunlight can also cause damage due to the resulting heating of the exposed materials. Color slides in particular are very vulnerable to fading when projected in a slide projector (due to both heat and light exposure). It is important to note that Kodachrome slide film is very stable in the dark but fades rapidly when exposed to light, while Ektachrome slide film is more resistant to projection damage but fades more quickly than Kodachrome in dark storage. Fujichrome is generally the most stable slide film overall.
For glass plate negatives and transparencies, storage should be cool (approximately 65°F with low, stable humidity (30-40% RH +5%). Lower humidity will cause the image emulsion to flake off while higher humidity may corrode the glass support.
Scrapbooks pose challenging preservation problems because they frequently contain a variety of components and media. In addition, they are often unique, fragile, damaged, or of significant associational value. If they must be interfiled within archival collections, they should be well-supported and separated from direct contact with other materials.
Scrapbooks that have informational value alone (for instance, clippings scrapbooks) can be photocopied onto archival-quality paper and/or microfilmed. The originals would then be retired from use and copies made available to researchers. Scrapbooks that have enduring value in their original form should be individually wrapped in archival-quality paper and/or boxed in custom-fitted boxes. Valuable scrapbooks may have a high priority for evaluation by a conservator. See Preservation of Scrapbooks and Albums on the Library of Congress website for more information.