Microforms
Microforms includes both microfilm and microfiche. Microfilm comes in roll form. It was developed more than 100 years ago as a part of conventional photographic technology. Early microfilm has been generally stable. If microfilm has a quality polyester film base, is exposed and processed to international standards, is housed in stable protective enclosures, and is stored under the appropriate conditions. It will last for a minimum of 500 years. The longevity issue is vitally important, as it defines the main difference between microfilm and other reformatting technologies such as digital imaging.
Microfiche usually replicates multiple individual pages in single fiche sheets. It can be made up of strips of film cut from rolls and placed in polyester jackets, or made by filming with a “step and repeat” camera, with images imposed directly onto a single sheet of film.
Microfilm is available in 16 or 35 millimeter widths with 35 millimeters the norm for preservation filming. Microform is now available as silver-gelatin, diazo, and vesicular**.**
Silver-gelatin
Silver-gelatin is the only type recognized for preservation or archival purposes. The image is captured by exposing silver compounds to light. Wet-processed silver film is the only type that can be recognized as archival, as dry silver film is not fixed by chemical processing and washing.
Diazo
Diazo refers to the diazonium salts used in the coating layer. The salts are combined with dyes to produce the image. Because diazo is strongly affected by ultraviolet radiation, especially in a reader machine, this type of film can fade.
Vesicular
The word vesicular derives from vesicles, or bubbles that form when an image is developed through heating, which causes nitrogen from diazonium salts to expand. Ultraviolet is then used to decay the salts. Pressure on the film can damage the image-bearing bubbles, and faulty processing can cause the bubbles to burst, resulting in damage to the image.
Other types
Other microform types include color and continuous tone. Color film is vulnerable to fading. years Continuous-tone film techniques can produce gray tones not captured by the high-contrast film used for normal filming. Continuous tone can be produced by various methods. These include processing silver-gelatin film by varying exposure time, and processing with a low-contrast developer.
Standards
An influential longevity estimate is stated in the International Organization for Standardization (ISO) standards, especially ISO 18901-2002. This standard refers also to other ISO standards that establish requirements affecting the longevity of microfilm. The 500-year estimate is based on independent laboratory tests using artificial aging techniques and observation of film over a considerable time. (ISO standards are available at www.iso.ch, or may be purchased in paper from the ISO offices in Geneva.) The American National Standards Institute (ANSI) also has stringent standards for the production and storage of microfilm; they may be accessed through www.ansi.org.
Another important document that describes longevity is in the context of U.S. National Archives procedures. The information in this document also addresses issues relating to the use of dry silver film as opposed to wet-processed silver-gelatin film. Dry silver film is never “fixed” (with light-sensitive silver salts removed), and it can be developed for an indefinite period of time. Thus if dry silver film is exposed to temperatures exceeding 50°C, it will continue to develop and turn black.
The storage of microfilm is an especially vital issue, and one that has been difficult to address in developing countries, although there are standards available. In 1998 a detailed survey of master microfilm negatives in one Southeast Asian country demonstrated that poor storage conditions had resulted in the loss of the textual content of most master microfilms filmed less than twenty years before. Fortunately, because positive copies of the microfilm had been deposited in other countries, it will be possible to reconstruct the negatives, albeit at a reduced level of quality and a high cost. It will be difficult to persuade a funding agency to invest in recreating these negatives.
Standards exist for every aspect of microfilm production, housing, and storage, and producers of preservation microfilm must honor these standards, whether the work is to be performed in house or by a vendor. With microfilm vendors, it is imperative that standards be incorporated in a “request for proposal” (RFP) and embedded in contracts. Knowledge of standards and evidence that they are followed are important points to make in seeking external funding to support microfilming projects.
View a select list of standards content (will open a new window) from ANSI and ISO.
Film Generations
Preservation microfilm is intended to be permanent, and for this reason, three generations are produced: the camera or master negative, the print master negative, and the positive-use copy.
Camera negative
The camera negative should be regarded as the archivalgeneration, and it should be used to produce one other negative for printing or reproducing positive copies. The archival storage of the master negative is important, as it ensures that the camera-negative quality is not reduced by generational loss or the making of multiple copies. The camera negative must be stored in a secure place remote from other film generations, and under consistent environmental conditions.
Print master negative
The print master negative is used to create the original positive copy and any additional copies requested by outside libraries. Under no circumstances should the print master negative, or the camera negative, be used by readers.
Positive copy
The positive copy is what readers use. If the copy is of a popular work, such as a national newspaper, it can suffer considerable damage through careless handling and poor storage. Review of the positive copy is important so that new copies can be made from the print master when necessary. Some institutions are able to support the cost of their microfilming efforts through the sale of positive microfilm copies.
Storage
As noted, the storage of microform is critical to ensuring its longevity. Even if the film base, capture procedures, and processing conform to standards, substandard storage can rapidly negate all the care taken. Master negatives are used only when the other generations of film are exhausted from use, and it is devastating when they are found to be unreadable because of poor storage. One of the basic lessons is to duplicate and distribute film copies to avoid the possibility of complete loss. Ideally, master negatives should be stored in a safe, fire- and flood-proof environment with a constant temperature of 18°C and relative humidity of 35 percent. The air filtration system in the storage facility should remove harmful chemical pollutants and provide adequate air circulation.
To repeat, the camera negative must be stored far from the other film generations. In the United States, research libraries store their camera negatives in very stable underground storage complexes such as the National Underground Storage/Iron Mountain facility in Boyers, Pennsylvania. (See http://www.ironmountain.com/ for services available.) Such storage opportunities are rarely available in developing countries, so some consideration should be given to inter-institutional cooperation in securing facilities.
The enclosures in which film is housed should also be taken into account when trying to extend the life of preservation film. If the storage facility is acceptable, high-quality acid-free, buffered board/paper boxes are the best and most economical way to house film reels. There is some evidence that sealed, nonferrous metal or certain plastic containers might slow down the process of deterioration in unsatisfactory storage conditions, but not for acetate film. One type of enclosure that can combat industrial pollutants is made from a MicroChamber board, which uses zeolite to absorb and neutralize most pollutants (see http://www.conservationresources.com/).
Microfilm Production
Generally, before microfilming a book, newspaper, or collection, it is important to discover whether or not the title has been filmed by some other institution. If the library belongs to a consortium, has access to an interactive bibliographic database such as OCLC or RLIN, can access an up-to-date list of master microforms for the region, or has printed lists of filmed titles, some careful checking should be done before the risk of duplicate filming is taken. However, given the generally poor standard of microfilm storage, claims by other institutions of having the microfilm available for purchase should be treated with caution, especially for titles filmed ten years or more ago. The preservation professional should use careful inquiry to discriminate between credible and suspect film holders.
Titles that are microfilmed should be fully catalogued. If possible, the interactive database record should be marked to show that the title has been “queued” for filming. This informs other libraries that you intend to film the title. Filming must be done soon after the queue has been recorded. When the filming is complete, the record should be altered to reflect that the title has been filmed and a new record created.
Over the last several years, printed lists of master microforms have been published for various regions of the world, and while these are useful, there is inevitably a publication lag, with some microform created but not reported for one to two years. Lists, whether paper or electronic, reflect only those titles reported to them, and there is no guarantee that older film will be usable. Clearly, an active consortium of dedicated librarians could play a critical role in reversing this problem.
Materials queued for microfilming should be collated to ensure completeness and should have eye-legible targets to be captured, along with the title, by the camera. There are standards for bibliographic and technical targets to ensure consistency of approach.
Special processing
Protection for microfilm can be improved through the use of polysulfide treatment, which greatly retards damage from pollutants. Polysulfide treatment, developed by the Image Permanence Institute of Rochester, New York, USA, can be added at the film-processing stage. Polysulfide solutions prevent “redox” blemishes by converting a percentage of the silver in the film into more stable silver sulfide. The treatment can be used during initial processing of film or for film already processed.