Former Director of Field Service
Northeast Document Conservation Center
Amidst the bells and whistles of the digital revolution, preservation microfilming quietly maintains its status as a highly valued and widely practiced preservation reformatting strategy. And why not?
The enduring popularity of preservation microfilm is because of its practicality. Unlike its digital counterpart, microfilm is the product of a nearly static, tested technology that is governed by carefully crafted national standards. When created and stored according to these standards, microfilm boasts a life expectancy of 500+ years. 1 It is also worth noting that, while digital data require use of a sophisticated retrieval system to access their treasures, microforms (i.e., microfilm and microfiche) can be read by the naked eye using only light and magnification.
The access potential of microforms admittedly pales in comparison with that of digital technology. Still, microforms can enhance access to information that would otherwise be unavailable because the original item is at a distant site or is vulnerable to damage and/or loss through handling. Also, microforms are relatively inexpensive to produce and to copy.
One key indicator of the continuing relevance of preservation microfilming is its ongoing support at the national level.
The National Endowment for the Humanities (NEH) continues to support the preservation microfilming of brittle books and serials through its Division of Preservation & Access.
In 1989, the U.S. Congress authorized NEH to implement a twenty-year initiative to preserve the intellectual content of approximately three million brittle volumes from research collections across the United States. According to George Farr, Director of NEH's Division of Preservation & Access, seventy-two libraries and library consortia, located in forty-two states, have participated in this cooperative effort thus far. When currently funded projects are completed, an estimated 862,418 volumes will have been microfilmed.
Through the years, microforms have appeared on various film bases, including cellulose nitrate, cellulose acetate, and polyester.
Cellulose nitrate-based microforms, like other cellulose nitrate films, are highly flammable, prone to releasing hazardous gases over time, and subject to natural decomposition. By the early 1950s, commercial production of all formats of cellulose nitrate film had permanently ceased.
Cellulose acetate film, touted as safety base film and non-flammable, will still naturally degrade over time. This degradation process is accelerated when acetate film is not properly stored. Although a great deal of acetate microfilm exists, acetate film is not acceptable as a preservation medium for microforms.
Polyester is the only film base currently recommended for preservation microfilming. Both stable and durable, black-and-white polyester film has a life expectancy of 500+ years under proper storage conditions.
Microforms come in a number of formats. The most familiar of these are 16mm or 35mm roll microfilm and microfiche, the latter resembling a plastic file card. Roll microfilm, in either 16mm or 35mm formats, can be cut into short strips and housed in clear "jackets" to produce a microfiche. Three types of film are common in microform collections: silver-gelatin, diazo, and vesicular.
Silver-Gelatin (or Silver-Halide) Microfilms
These are based on the familiar technology of black-and-white photography and are the only microform medium appropriate for archival purposes. The image is produced by exposing light-sensitive silver compounds in a film emulsion to light. The resulting image is chemically developed, but potentially harmful chemicals are washed out in processing. The original (master) silver-gelatin microfilm is almost always a negative image, but positive or negative duplicates can be made. The emulsion side of this film is matte, while the non-emulsion side is glossy. Modern silver-gelatin films are long-lived under appropriate storage conditions and normal library use.
These contain diazonium salts in the coating layer that combine with dye couplers to produce strong, dense colors. Exposure to UV radiation causes the salts to decay and to lose this coupling capacity. In the diazo process, film is exposed by contact printing from a master. Acids used in the coating to prevent the coupling reaction are neutralized by exposure to a strong alkali (usually ammonia), and dyes form in unexposed areas of the film. The image duplicates the master directly. Diazo film is available in a variety of colors, including black. It may have an acetate or polyester base, although polyester is increasingly popular because of its stability and resistance to environmental factors. Resistance to fading depends on the choice of salt and dye coupler; black requires a combination of dyes. Processed black diazo resembles silver gelatin film but is glossy on both sides. Diazo film is reasonably stable but eventually fades, even in the dark. Fading is accelerated by prolonged exposure to light (as in a film reader).
These take advantage of the fact that diazonium salts produce nitrogen as they decompose upon exposure to UV radiation. In vesicular films, diazonium salt coating is sandwiched between two base layers. The film is exposed via contact printing from a master, and the image is developed by heating the film. This momentarily softens the base material and causes expanding nitrogen to form tiny bubbles (or vesicles) that remain when the film is cooled. Typically, residual photosensitive material is then fixed by exposing the film to UV radiation, causing complete decay of the diazonium salts. Incident light passes through the clear areas of the film but is scattered and reflected by the bubbles, causing those areas with vesicles to appear dense. The image will always exhibit slightly raised areas. The film base is always polyester because acetate cannot tolerate the heat used in processing. Vesicular film can easily be damaged by mechanical pressure, which can collapse the bubbles. Another major vulnerability of vesicular film is bubble migration or movement. At high temperatures, the base material softens allowing the gas contained in the bubbles to expand. As the bubbles grow in size, they can rupture, leaving patches of clear film where the image was formerly visible. Vesicular film may suffer damage at temperatures below 167°F, the American National Standards Institute (ANSI) permissible temperature for film readers; so special care is warranted when this film is used in a film reader.
In recent years, interest in color and continuous-tone microforms has grown in the preservation community. A brief discussion of these microform types follows.
Color Microfilms and Microfiche
Though there are many potential applications for color microforms, use of this technology cannot accurately be considered a preservation strategy because the life expectancies of most 35mm color films fall far short of preservation goals. Yet there is one (positive) color transparency film, Ilfochrome, that is considered quite promising for preservation. Unlike other color microfilms, which generate their dye image during processing, this film has color layers built directly into its emulsion. Testing at the Image Permanence Institute (Rochester, NY) suggests that the life expectancy of the dyes is excellent — possibly 300 to 500 years — when the film is not exposed to light. The research also suggests, however, that the film's polyester base may be less resistant to deterioration than some other polyester bases. Even so, the life expectancy of the base may be as much as 200 years or more. No testing of light stability (important to estimate permanence in use) has yet been done.
Quality black-and-white microfilming yields a high-contrast negative with excellent text resolution. Unfortunately, high-contrast microfilm cannot ordinarily capture a broad spectrum of gray tones; thus, what is gained in text resolution is lost in reproducing halftone photographic images and illustrations. Continuous-tone microfilming attempts to maximize gray scale reproduction without sacrificing textual resolution. A variety of methods can be used to create continuous-tone microfilm. For example, one preservation microfilming vendor uses Kodak 2470 direct duplicating silver gelatin microfilm in the camera and exposes the film for a prolonged time (exposure time can vary) under halogen lamps. Another, uses Fuji SuperHR20 film at normal shutter speed and achieves continuous-tone results primarily through processing in a low-contrast developer at a slower than normal processing speed. In either case, a wide range of gray tones can effectively be captured.
Microforms used for long-term preservation of information require careful production and examination in addition to well controlled storage and handling conditions. Curators and managers of collections that use microforms should establish specifications to insure that vendors provide films to meet their use and preservation needs. ANSI/Association for Information and Image Management (AIIM) standards, as well as specifications developed by the Research Libraries Group (RLG) and by the Library of Congress, are useful guidelines. Each institution's requirements will differ, however, and these requirements should be contractually specified and systematically monitored to protect the collections themselves and the institution's interests.
The AIIM Standards Catalog can be browsed online at: www.aiim.org/industry/standards/97stdcat.htm .
In order to ensure that contractual specifications regarding film quality have been achieved, microfilm vendors should thoroughly inspect processed first-generation film, including: a frame-by-frame inspection to detect filming errors (e.g., focus problems, overexposed images, underexposed images, etc.), visible defects (e.g., fingerprints, scratches, etc.), missing pages, and the number of splices on each reel; a resolution test using either the Quality Index or the systems resolution method described in ANSI/AIIM MS23-1998; density readings, interpreted according to the guidelines in the RLG Preservation Microfilming Handbook; and a methylene blue test to detect the presence of residual thiosulfate (see ANSI/NAPM IT9.1-1996). The microfilming vendor should also take density readings on all second- and third-generation duplicates to ensure compliance with specifications, and should subject all duplicates to a lightbox inspection for legibility and contrast. Results of all quality-control inspection done by the vendor should be submitted to the contracting institution on a quality-control report form.
The responsibility for quality control should not rest exclusively with the vendor. The institution should also conduct its own inspection to determine compliance with contractual specifications. A practical guideline can be found in Appendix 18 of the RLG Preservation Microfilming Handbook (listed in the bibliography under "Elkington").
Temperature and Relative Humidity
In general, microform requirements resemble those of other photographic materials. Year-round relative humidity lower than 50% is recommended for all film types. An upper limit of 40% is recommended for silver-gelatin films to minimize the likelihood of microscopic blemishes from silver oxidation (sometimes called "measles"). Temperature should not exceed 70°F; cooler temperatures are preferable. Master films should be stored at maximums of 65°F, 35% RH, ±5%. ANSI/NAPM IT9.11-1993 and ANSI/PIMA IT9.2-1998 specify exact conditions for archival storage of film.
If low temperatures are maintained for the storage of collections, and if readers are located outside of the storage areas, a conditioning period is required to allow gradual warming of cold films before they are read. Rapid transfer from a cold to a warm space may cause water condensation on the surface of the films.
Dehumidification systems should be refrigerant based. Desiccant-based systems can generate fine dust particles that may scratch the surface of films. Desiccant-charged storage cabinets are not recommended for use with microform collections; the relative humidity in such a system is difficult to monitor and control, and dust may abrade film surfaces. If humidification is required to stabilize fluctuations in the storage environment, it should be derived from a system with a contaminant-free water source. Corrosion inhibitors used in many large-scale systems can leave reactive deposits on library and archival materials. Film is particularly susceptible to chemical and abrasive damage from this source. Trays of water or chemical solutions should never be used to humidify storage cabinets.
As in the case of paper artifacts, fluctuations in temperature and relative humidity must be controlled for long-term preservation. Relative humidity and temperature for microform collections in use should not vary more than ±5%, and ±3% is preferable. The cooler the storage and the better controlled the relative humidity, the longer the expected life of the films.
Particulate air pollutants are an obvious source of scratches and abrasions for microfilm. Silver-gelatin films are particularly vulnerable to such damage. House cleaning, including regular vacuuming, is important in storage and use areas.
Gaseous air contaminants, e.g., oxides of sulfur and nitrogen, paint fumes, ammonia, peroxides, ozone, and formaldehyde, damage film bases and emulsions. These contaminants may produce oxidizing or reducing effects that cause microblemishes on silver-gelatin films; precautions must therefore be taken to reduce the risk of exposure. Microforms should not be stored near photocopiers, which may be a source of ozone. Also, microforms should be removed from any area to be painted; good air circulation should be provided by fans and open windows, and paint should be allowed to cure for three months before films are returned to the space. Wooden shelving or cabinets should not be used in areas where microforms of long-term value are stored.
Diazo, vesicular, and silver-gelatin films should not be rolled on the same spools, sleeved in the same enclosures, or (ideally) stored in the same containers. Space and access problems usually make separate cabinets for different film types impracticable, but separate spools and fiche sleeves should always be used. In addition, older vesicular films may be a source of acidic deterioration products. They should be physically separated from other films and systematically replaced.
While perfectly controlled storage environments are ideal, multiple copies of microforms can provide a pragmatic solution for archival preservation. Most collections with film of enduring value use a three-generation system to allow some flexibility in storage requirements.
The first generation film (or master negative) should be a silver-gelatin negative produced from the original artifact and processed according to standards given in ANSI/AIIM MS23-1998. This is the archival copy, which is used to produce a duplicate negative (see below) for the generation of use copies. The master negative should be stored in a different location from secondary copies and under conditions as close as possible to the ideal. There are a number of repositories that rent space for the archival storage of microfilm. These are recommended, but the user should be sure the storage conditions at the chosen facility meet ANSI standards outlined in ANSI/NAPM IT9.11-1993. The only subsequent use of the master negative should be the reproduction of a duplicate negative lost to damage or disaster.
Duplicate Negative (or Print-Master Negative)
This copy is almost always silver-gelatin. The duplicate negative is used to generate use copies (see below) for the collection. It should be stored under the best available conditions, since it serves as a working master, to protect the master negative. Ideally, it should be physically separated from use copies.
Use Copies (or Service Copies)
Any of the available media or formats may be acceptable, and images may be positive or negative. Good storage and handling will extend the life of use copies, thus protecting previous generations of microforms.
Since it is difficult with available technologies to completely remove gaseous contaminants, it is important to enclose polyester films well. (Older acetate films, however, can off-gas acetic acid and should therefore be well ventilated or sealed with molecular sieves.) If master polyester negatives must be stored in poorly controlled environments, sealed metal cans or inert plastic containers may provide a solution. Kodak publication D-31, Storage and Preservation of Microfilms (Eastman Kodak Company, Rochester, New York, 14650) offers valuable guidance for the use of sealed containers. This strategy is not a panacea and must be used judiciously. Cans, to be acceptable, must meet chemical composition requirements. It will be necessary to examine the film periodically to make sure that no deterioration is occurring. Guidelines for inspecting silver-gelatin film are offered in ANSI/AIIM MS45-1990. If no deterioration is evident, the film can then be returned to the conditioned cans. The preferred means of storing master film is in a preservation-quality box and in a temperature- and relative-humidity-controlled facility.
Enclosures should be chosen following established guidelines for archival storage and should all pass the Photographic Activities Test as performed by the Image Permanence Institute. NEDCC recommends that paper enclosures be of high-quality, lignin-free, buffered or neutral paper. MicroChamber storage boxes (produced by Conservation Resources International, Inc., of Springfield, Virginia) are made from a board impregnated with zeolites, which neutralize gaseous pollutants. Use of these boxes appears to increase film life significantly in environments that are heavily polluted with ozone, peroxides, and other compounds that attack microfilm; it may also slow deterioration from chemicals off-gassed by older, non-preservation-quality film.
If the relative humidity of the storage environment is stable and below 50%, buffered enclosures should present few, if any, problems. Where possible, adhesives should be avoided. Safe plastics, such as polyester, polyethylene, or polypropylene, but not polyvinylchloride (PVC) or vinyl, are acceptable. Microfiche should be sleeved with the emulsion side away from the interior enclosure edges to prevent abrasion; this also adds protection from adhesives on sealed edges. Microfilm reels should be individually boxed, with film held in the wound position by a preservation-quality paper tag secured with a string and button tie. Rubber bands contain residual sulfur, a source of film and emulsion damage, and must never be used.
Steel filing cabinets are most desirable for microform storage, but inert plastic containers are acceptable for library shelf use. Microfiche enclosures should fit without buckling into drawers. Dividers and placement guides should be made of pH neutral materials. Do not compress fiche in filing, and use space dividers to prevent curling. As noted, different types of film should be stored in different containers to prevent chemical interactions. Filing systems should be designed to minimize handling, and storage cabinets should facilitate the location and retrieval of information. Wear is inevitable in used collections, but its speed and severity can be controlled.
Since acidic oils and fingerprints can damage film, users should always wear gloves when handling master negatives. All films should be handled by the edges or leaders. Only one microform at a time should be removed from its enclosure. Fiche should be resleeved immediately after use; film should be immediately reboxed. In addition, rolled film should never be pulled tight on the reel as this can cause abrasions. Education of staff and users regarding the proper handling of microforms is essential to the longevity of the film.
Ease of use and maintenance should be considered in choosing equipment. Microform readers generate heat; ANSI standards specify an upper limit of 167°F for temperature at the film plane. Some diazo films are damaged at this temperature, and prolonged exposure of small areas of film (e.g., a single frame) should be avoided for this reason. As mentioned above, vesicular film damage can occur at temperatures below the ANSI limit, so special care is warranted. Microform-reading machines should be turned off if the user leaves the equipment.
Reader lens size should take into account the reduction ratios used for filming. In preservation microfilming the image is usually reduced between 8x and 14x, so lens magnification should be in similar ratios. Zoom lenses, which allow for changing magnification, are available.
Equipment should be inspected weekly and maintained daily. Dirty equipment will decrease image quality. A staff member should have assigned responsibility for equipment maintenance and should be trained by the manufacturer's personnel. Dust on the glass flats will be magnified by the optics of the reader. Dust can also be transferred to the microform, where it might obscure details and even damage film. Dust covers should always be used whenever the film reader is not in use. Grime builds up on the edges of glass flats to create another source of film abrasion. For this reason, glass flats and carriers should be cleaned daily. A regular schedule for cleaning lenses, mirrors, and the matte surface of viewing screens should also be established, but this cleaning must be done with extreme care as these items can be easily damaged and/or made to appear smeared or mottled. Instructions for equipment maintenance are beyond the scope of this report. General instructions are given in Francis Spreitzer's Microforms in Libraries (see Further Reading, below).
Disaster planning is critical for microform collections. Microforms are highly susceptible to water damage. They must be protected from flooding or burst pipes. Once wet, this material must not be allowed to dry in rolls or enclosures as it will stick to itself and to the enclosures. Wet microforms must be removed from their enclosures. Rolled film must be unrolled for drying. Air drying is acceptable, but it is most efficient to locate, in advance, a local film processing lab that can provide this service in the event of an emergency. Microfiche can be dried flat, emulsion side up, in single layers or clipped to a line by an edge that bears no image. Diazo is prone to water spotting, and squeegees or lint-free pads should be used to control beading.
Wet microforms should not be frozen or freeze-dried since film layers may separate as a result and handling damage is difficult to prevent. If microforms cannot be air-dried immediately, they must be immersed in clean, cold water and sent to a laboratory for safe washing and drying. Mold growth must be prevented on all film types. Moldy diazo and vesicular films may be cleaned with a slightly moistened lint-free pad; if mold infects silver gelatin-film, seek professional assistance.
Commercial microfilmers are often a cost-effective provider for converting books and documents to microform. As stated above, each institution should develop standards for its microfilm, and these standards should be part of the contract for services. It is a good idea to visit the microform provider to make sure that environmental control, fire protection, housekeeping, and security meet the needs of the collections that will be filmed. This is especially important to prevent damage to original materials that will be returned to the collection rather than being discarded.
In some cases, a special-service filmer is appropriate. Many objects are filmed because they have become too fragile to survive handling by researchers. If that is the case, or if the institution wants to retain bound materials in their original form, a special-service filmer should be considered. High-volume commercial microfilmers lack the equipment, time, and expertise to process fragile materials without damage to brittle paper or deteriorated bindings. Costs for special service will be higher, but valuable artifacts or hard-to-film originals (e.g., tightly bound volumes with narrow gutters or documents with fading or inadequate contrast) may require this expense. Contact a preservation professional for advice.
The author is grateful for the significant contributions made by Karen Motylewski, who wrote the original preservation leaflet updated here, and Robert Mottice of Mottice Micrographics, who served as technical editor for this revised version.
Elkington, Nancy E., ed. RLG Archives Microfilming Manual . Mountain View, CA: Research Libraries Group, 1994, 218 pp.
Fox, Lisa L., ed. Preservation Microfilming: A Guide for Librarians and Archivists , 2nd ed. Chicago: American Library Association, 1996, 394 pp.
McKern, Debra, and Sherry Byrne. ALA Target Packet for Use in Preservation Microfilming . Chicago: American Library Association, 1991.
Recommended Practice for Operational Procedures/Inspection and Quality Control of Duplicate Microforms of Documents and from COM , ANSI/AIIM MS43-1998.
Recordak . Storage and Preservation of Microfilms . Kodak pamphlet no. P-108. Rochester, NY: Eastman Kodak Company, 1985.
Reilly, James, et al. "Stability of Black-and-White Photographic Images, with Special Reference to Microfilm." Abbey Newsletter 12.5 (July 1988): 83–87.