Photographs record and store information regarding events, history, and people and provide through study a basis for the development of new information. Photographs are also an art form, comprising images created with a variety of techniques, such as the daguerreotype, tintype, and black-and-white and color prints. The process used to create each format is unique, however, the basis for producing photographs remains constant: exposing a mixture of chemicals on paper, film, or glass to light. The outcome of photography is both an image negative and a positive print image. Photographs and photographic paper are chemically complex structures and as such are more fragile and susceptible to adverse conditions than paper. Many steps can be taken to assist in the preservation of the information provided in photographs.
Photographs are susceptible to destruction caused by excessive exposure to light and physical and environmental fluctuations and hazards. They should be stored in an environment that does not have high temperature and high humidity or excessive fluctuations in temperature and humidity. An ideal temperature is 68° Fahrenheit with a relative humidity range from 35 percent to 40 percent.
Direct handling of photographs or touching the surface of a photograph should be avoided because oils and chemicals on human skin can permanently damage a photograph. Photographs should be protected from airborne pollutants, improper handling, as well as fingerprints, abrasions, dirt, pencil or pen marks, paper clips, and cracked surfaces. Photographs should be stored individually in paper that is acid-free or in plastic enclosures that are chemically inert. Paper enclosures protect images from light and avoid potential moisture buildup. Plastic or polypropylene or polyethylene enclosures allow an image to be seen without removing the image from the enclosure. Photographs are best stored in a dark closet on the first or second floor of a house, never in a basement or attic.
Slides consist of a transparent base, made from glass or film, that allows an image to be projected onto a screen. Both black-and-white and color slides are affected by the same environmental factors as photographs on paper. When slides are projected, the image is exposed to a great amount of both heat and light that adds to the deterioration of the slide. Slides are also affected by the acid content of cardboard sleeves or by the type of plastics used in the sleeves for the transparent image. Slides, as well as negatives, need to be treated with the same care and environmental considerations as print photographs.
Motion Picture Film, Audiotape, and Videotape,
Films provide information in visual and audio form and are also considered to be artistic works. Motion picture film, both black-and-white and color, is composed of multiple layers that, due to their chemical components, can react to bad environmental and physical factors. Motion picture film is plastic that is made of nitrate, acetate, or polyester. Each of these types of film is coated with a chemical emulsion that holds the actual images.
Nitrate-based film, used prior to the 1950s on 35-mm format, is particularly unstable and can deteriorate rapidly in most storage conditions. It is highly flammable and the gasses emitted from the nitrate can invade and affect surrounding films. Because of these factors, nitrate film should be stored separately from all other materials in a collection. It should never be stored in an area that also serves as a living, working, or archival storage space for other materials. The deterioration of nitrate film can be slowed through stable cold storage at a temperature of less than 25° Fahrenheit. However, the best preservation option is to transfer nitrate film to modern, chemically inert polyester-based film.
Acetate has been used for 8-mm, 16-mm, and 70-mm film formats. Acetates are known as “safety” film because, unlike nitrate, they are not combustible. The plastic of the film can react with the atmosphere and create an acidic byproduct that gives off a vinegary odor, a form of deterioration known as “vinegar syndrome.” This cannot be reversed and can spread to other films. Again, the best preservation method for nitrate-based film is transfer to polyester film.
Polyester is chemically inert and does not exhibit the same problems as nitrate-based and acetate-based films. All films are best stored horizontally, in chemically inert canisters, and in a controlled environment. High or fluctuating temperature and relative humidity can damage film by attracting mold, separating the emulsion layer of a film from its base, and accelerating chemical deterioration. Motion picture film should always be protected from light, dust, dirt, and fingerprints. All motion picture film is fragile and its base and emulsion layers can be easily damaged with improper handling or use in either a viewer or projector. For this reason, alternative copies may be produced for greater access to the information or content of the film.
Videotape, another common format for moving images and sound, may contain information that is considered highly popular, such as a copy of a popular movie, or may contain personal information, such as home videos. Videotape is an electromagnetic medium and as such is also highly affected by fluctuations in temperature and humidity, dust and dirt, use in poorly maintained playback machines, and magnetic fields. Videotape is not considered an appropriate medium for long-term preservation. Each time a videotape is played it loses some of the picture quality or signal. One way to ensure that the content of a videotape is not lost is to transfer it to polyester motion picture film and store it accordingly.
Audiotape, commonly found in cassette and reel-to-reel format, is subject to the same environmental and handling concerns as videotape. Analog reel-to-reel tape offers high-quality sound reproduction and is still considered the best preservation format for recordings on magnetic media. Audio-cassettes, which also consist of a magnetized plastic ribbon, are more accessible and less easily mishandled that reel-to-reel tapes, but their sound quality is significantly inferior. The temperature and humidity should not fluctuate and a temperature range from 60° to 70° Fahrenheit and a range of 20 percent to 30 percent relative humidity is best for storage. As with any audiovisual format, the equipment used to play tapes should be maintained in proper condition, kept free of dust and dirt, and the tape ribbon should be aligned properly on the reels to avoid distortion. It is also best to create copies of original tapes for access and use.
Preservation of moving images on film and videotape and of sound recordings on audiotape is important due to the unique information these formats contain. Yet their chemical and magnetic components, and their dependence on machinery that may become difficult to maintain or become obsolete, makes the preservation of the original format a challenge. For these reasons, audiovisual materials become candidates for transfer to a new format.