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 in the context of U.S. National Archives procedures may be found at http://www.archives.gov/federal_register/experimental_format/proposed_changes.pdf. 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.
Click on the link below to view a select list of standards content from ANSI and ISO.
