3. Microform Terminology
Chapter 3 of Managing Microforms in the Digital Age
During the twentieth century, many types of microforms were developed. Some types were short-lived, while others became standardized and were widely used. The presentation format of microforms, the composition of microforms, and the components of quality.
Microfilm or roll film is wound onto a standard size spool or reel. Reels can accommodate up to 125 linear feet of 4 or 5 millimeter-thick microfilm. Roll film comes in standard widths of 16mm and 35mm. Rarely, 105mm film is used for architectural drawings or blueprints with one image per frame. 35mm film is used most commonly for books, journals, newspapers and archival materials. Business and agency records are often filmed on16mm film. An advantage of 35mm microfilm is that it permits small reduction ratios (3.3.1) and thus larger, clearer images.
Some micropublishers offer these formats in cartridge or cassette form. A cartridge is a plastic enclosure around the roll of film. It protects the film, makes it easier to handle, and, frequently, is self-threading. When in use, film from a cartridge is wound on a separate spool. A cassette is similar to a cartridge but has a double core so that film never leaves the container. The suitability of these two convenience packaging devices depends on the library's equipment and long-term plans for its microfilm program. It is far more common to have 16mm, rather than 35mm, microfilm packaged in cartridges.
All microfiche are a series of microimages on a flat sheet of 105mm film arranged in a grid pattern. The content is filmed onto 105mm film stock, and then the roll film is cut into sheets. The most common size of microfiche now being produced measures 4 x 6 inches (105mm x 148mm). Some 3 x 5 inch (75mm x 125mm) microfiche are still available, but this size is gradually falling out of use. The standard 4 x 6 inches format is usually offered in a format of 60 or 98 pages per fiche. These two formats are usually filmed at reduction ratios (3.3.1) of 20:1 (20x) or 24:1 (24x). Microfiche filmed at much higher reduction ratios are called ultrafiche. Technically, microfiche filmed at high reduction ratios are classed as follows: high reduction, 30x to 60x; very high-reduction, 60x to 90x; and ultrahigh reduction, 90x plus. For the same size fiche, microfiche produced at these high reduction ratios can accommodate many more pages per fiche than those filmed at conventional reduction ratios. The disadvantage to high-reduction documents on fiche is that the clarity of the text will be diminished.
Microfilm and microfiche reading equipment comes in many sizes and feature many functions. Some are simply readers with no printing functions. Some are dedicated to one format: roll film or fiche. Others are multifunctional machines with viewing, printing, and digital functions serving 16mm/35mm film and fiche formats. Some patrons prefer the large format screen of some readers, particularly for browsing newspapers on film. Others are satisfied with smaller, more compact screens that feature zoom and crop capabilities.
Microopaques contain a series of images arranged in a grid-like pattern on a paper or card substrate rather than a film base. Microopaques, also known as Microlex cards, Microprint or simply microcards, are no longer produced. The original microcards were produced on 3 x 5 inch cards and contained approximately forty document images. Other microcard formats measured 6.5 x 8.5 inches, containing two hundred images and 6 x 9 inches, containing one hundred images. Microopaque collections require specialized reading and printing equipment.
An aperture card is a tabulating card with a single frame of 35mm film mounted within the open aperture. Aperture cards were widely used by the engineering and architectural industries to preserve drawings, blueprints, and maps. The standard aperture card measures 3¼ inches wide x 7 3/8 inches in length (86mm x 187mm). The reduction ratio is typically 24:1 (24x) to 30:1 (30x). Aperture cards require specialized aperture card readers and reader/printers.
Computer Output Microforms
Computer output microforms (COM) are made by writing a data stream directly from a computer to microfilm. The data stream, once printed to film, translates into miniaturized paper documents. COM are used in many records management applications. COM include 16mm and 35mm roll film, microfiche, and aperture cards. One specific type of COM is made with an electron beam recorder. E-beam technology produces high-quality microfilm and is used in some hybrid (digital and film) preservation projects. Kodak, Zeutschel, and other companies offer 16mm/35mm ArchiveWriters that ingest high-quality digital images and then write the images to 16mm or 35mm microfilm.
In the 1970s updatable microfiche systems were popular for active records management programs that required removal and destruction of obsolete information and the interfiling of information accumulated since the last update. Microfilm jackets are another form of updatable microfiche still in use in records management systems. A 16mm (or 35mm, which is far less common) strip of film can be inserted into a clear plastic carrier with channels that stabilize four to six strips of film. Out-of-date information can be removed, and new information can be inserted. Neither of these formats are suitable for records of permanent or long-term retention value.
Composition of Microfilm and Microfiche
All microforms are composite objects consisting primarily of a base, an emulsion and a binder that adheres the emulsion to the base. The chemical properties of the base and emulsion contribute to the longevity and quality of the film.
Types of Film Base
Cellulose Nitrate. Cellulose nitrate was the first stock used in film production. It was used commonly for motion picture film, government records, and studio photographic film applications. Nitrate stock was used less commonly for commercial microform production. Use of nitrate film was discontinued because it was highly flammable, even pyrophoric, and was prone to rapid deterioration when housed in improper storage environments. In the 1950s new, safer film stocks like cellulose acetate and cellulose triacetate were developed to replace cellulose-nitrate stock.
Acetate. Acetate film stocks were used during the heyday of large commercial microfilming projects from the 1950s through the mid-1980s. Acetate film, if properly prepared and properly stored, has a life expectancy (LE) of one hundred years. Acetate film stock can deteriorate rapidly in the presence of fluctuating temperature and humidity, particularly high temperature and humidity. The chemistry of the film breaks down and yields acetic acid which produces the noticeable aroma of vinegar, hence the name vinegar syndrome. At the point that the smell of vinegar is even faintly detectable, the rate of deterioration precipitously increases.
Vinegar syndrome results in the shrinking of the acetate base and the cockling and distortion of the emulsion which renders the films unusable. Storage of acetate films in cold or cool storage is the only way to diminish the rate of deterioration and is obviously not a practical solution for collections in a public service area. Institutions, however, which possess master negative collections comprising acetate films should make every attempt to store them in the proper environment to ensure their preservation. Another unfortunate feature of acetate films is that they tear easily and are easily torn during use on readers. The Image Permanence Institute’s IPI Storage Guide for Acetate Film and the ANSI/AIIM MS23 1998—Standard Recommended Practice—Production, Inspection, and Quality Assurance of First-Generation Silver Microforms of Documents provides the best advice about proper storage of acetate films.1 The American National Standards Institute (ANSI) establishes methods and practices that produce a consistent result. The Association of Image and Information Management (AIIM) identifies best practices for the consistent results for imaging technologies. Together, ANSI and AIIM work with curators, librarians, engineers, chemists, administrators, and other vested parties to produce standards that are rigorously vetted, accepted, and periodically revised.
Polyester. Polyester film stock is used almost exclusively today for microform production. Polyester is very chemically stable and physically durable. It is very tear-resistant. Libraries, archives, and micropublishers adopted polyester films in the 1980s. Polyester films have a life expectancy of five hundred years (500-LE) if properly prepared and stored. Once again, if an institution possesses a first-generation master negative collection, every effort should be made to store the negatives in the proper environment. And if the institution holds both master negatives and print masters of identical content, each generation should be stored in a different location in a climate-controlled environment to hedge against catastrophic disaster. The ANSI/AIIM MS23 1998 standard provides the best advice about proper storage of polyester films.2
The Difference between Acetate and Polyester. If a tiny sliver of film can be torn off, the film is acetate. Polyester is extremely strong and is very unlikely to tear. Tearing film is a destructive test, so consider employing other tests to help identify the base. If acetate film has started to deteriorate, the characteristic vinegar odor may be present. Old acetate fiche and films might have a cupped or curled appearance that develops as the acetate base shrinks. Polyester film wound on open-flange reels (reels that show the wound film) will pipe light through the wound pack. Hold the open-flange reel of polyester film up to a light source. Gray-white light pipes through the very translucent film. When acetate reels are held up to light, very little light pipes through, and the film appears dark and brown-yellow in color. Long-term microfilm managers, sound recording professionals, and other people who rely on their sense of hearing can identify roll film base by the sound it makes when a long strip (about two feet) is shaken. Acetate has a deep, dull sound, and polyester has a thin, tingly sound.
Types of Film Emulsions
Although there are many types of film, three are most commonly offered to libraries by micropublishers and suppliers.
Silver Halide. Silver halide is a specific type of silver gelatin film composed of very finely divided grains of silver. Silver halide is the most light-sensitive of all the films used in microforms, hence it can record the greatest amount of detail and provides the richest tonal variance. It provides the most faithful reproduction of the source document. ANSI and AIIM have established standards for the production, processing, and storage of this film as an archival medium. If properly prepared and properly stored, silver halide polyester microforms have a 500-LE.
Silver halide films have distinct dull and shiny sides. The dull side is the silver emulsion side of the film and the shiny side is the base side. Many librarians insist that microforms for their permanent collections be silver halide films. It is unlikely that most libraries have the proper environment in their microforms reading rooms for storing 500-LE film, so it is unlikely that many service collections will exist for a full five-hundred years. That said, properly prepared silver halide microfilm ensures the most faithful reproduction of the original documents and provides a researcher with the clearest images and easiest reading experience. The International Organization for Standardization’s, ISO 18901:2001 Photography, Imaging Materials—Processed Silver-Gelatin-Type Black-and-White Films—Specifications for Stability set forth the methods, materials, and processes that ensure a permanence factor of 500-LE.3
Diazo. Diazo is the generic name for films composed of light-sensitive diazonium. Ammonia fumes are used in the chemical processing of the exposed diazonium salts to produce azo dyes. The azo dyes of some diazo films may be subject to fading and loss of image. These films are frequently blue-black, purple-black, or brown-black in color, compared with the gray tones of silver halide. Diazo films appear equally shiny on both sides. Diazo films are very unstable in the presence of light and will fade easily, even when film is heavily used on microfilm readers. Diazo films are not considered archival quality and are primarily used for dispensable or frequently updated materials. Diazo films on polyester base and stored properly have a 100-LE. If improperly stored or if the diazo is on acetate, the LE is can be significantly shorter. ANSI IT9.5-1992—Imaging Materials—Ammonia-Processed Diazo Photographic Film—Specifications for Stability outline products and procedures for achieving 100-LE.4 Libraries often purchase diazo films because they are less costly than silver halide; however, as a long-term investment it is probably more prudent to invest in silver halide film.
Vesicular. Vesicular is a generic term for films having images consisting of small bubbles or vesicles. Vesicular film uses diazonium salts. Vesicular films are not chemically processed; rather heat is used to develop the vesicles that harden into images as the film is processed. All vesicular film is polyester-based. Vesicular film typically has light-blue tone and is considered fairly scratch-resistant; however, with heavy use or in the presence of high heat from readers, the bubbles can collapse or deform, distorting the images. ANSI IT9.12-1991—Imaging Materials— Processed Vesicular Photographic Film—Specifications for Stability articulate the processes and materials that achieve from 10-LE to 100-LE.5 Vesicular is a reasonable choice for materials of short-term retention or relevance. The issues of economy versus fidelity and permanence are the same as those when comparing diazo to silver halide.
Components of Film Quality
Reduction ratio is the degree to which a document is photographically reduced in size (miniaturized). Reduction ratio is expressed as a proportion between the linear size of the original and the linear size of the microform image. An item filmed at 14 to 1 (14:1) would have been reduced fourteen times. Reduction ratios are also commonly expressed as 14x, 16x, and so on. Average-size monographs, journals, and archival collections are usually filmed at reduction ratios from 8x to14x on 35mm film. Newspapers and oversize volumes are usually filmed at reduction ratios from 16x to 20x on 35mm film. Four-by-six-inch microfiche or 16mm microfilm contain documents filmed at from 20x to 50x reduction.
Polarity refers to the relationship of the color of the film’s background to color of the film’s image. Negative polarity means that white (or clear) images appear on a black background, while positive polarity signifies that black images appear on a white (or clear) background, as on a printed page.
Density refers to the opacity of the film. Density is determined by the length of time the film is exposed to light and by uniform illumination of the light source. To the viewer of the microform, the density could translate as the darkness or lightness of the film or, perhaps, as underexposure or overexposure. Micropublishers aim to have uniform density throughout the film, and they try to achieve a density that produces the clearest and crispest text. For black text on white paper in good condition, this is easy to achieve. For compromised source documents such as damaged newspapers or brittle books, uniform densities can be hard to achieve. A densitometer is used to derive the density values. During quality-control inspections, densities are checked throughout the microform to ensure that the densities are tightly controlled.
The generation of a microform refers to the number of duplication steps between the original source documents and the microform copy. There is a reduction in quality, legibility, or both in each successive duplication step. The camera film is the first generation, being one step removed from the original document. First-generation films sometimes are called camera masters or master negatives. Copies made from master negatives are the second-generation films. Most micropublishers make second-generation service negatives or print masters from which they produce multiple service copies for distribution.
Master negatives should be stored in a cold and dry environment to ensure long-term preservation. If silver halide polyester microfilm is properly prepared and stored, it has a life expectancy of five hundred years. Positive or negative microfilm or microfiche created from print masters are the third-generation copies.
Microfilm standards, fine-tuned in the 1980s, describe the methodology of creating third-generation films according to a metric for excellent legibility. This is known as the quality index, which operates on a point scale that guarantees high-quality third-generation film if the resolution of the first-generation negative falls into the high range of quality points. Generally, the fewer the generations, the better the legibility. Therefore, librarians and archivists should generally seek distribution films that are as few generations removed from the original material as possible, remembering, of course, that the first-generation camera master is not available for purchase.
Targets are the noncontent part of a microform. Targets are used to evaluate the quality of the film or fiche and are used to help the user understand the content of the microform. Targets are also used to help properly navigate a film or fiche. Some targets are required to certify that source documents merit long-term retention or that they are admissible as legal documents. Technical targets include resolution charts that are evaluated using a microscope to determine the focus and clarity of the text. Uniform density targets are evaluated using a densitometer to determine the level of density and its uniformity throughout the film.
Some targets are eye-legible, including brief title and author information, call numbers, accession numbers, and container or set numbers. Bibliographic records are included to identify the content and edition. Targets record the date of image capture, the name and address of the filming agency or micropublisher, the condition of the material prior to image capture, the type of image capture device, the type of film, and any of information about the source documents and the image capture technology that will help future researchers understand how and why the microform production occurred. Targets also indicate missing content and publication anomalies like issues not published on holidays, special supplement included, or change of frequency. The standards and specifications for the use of targets evolved in the mid-1980s. Early micropublishers rarely included detailed targets. In some cases, identification targets have been added over time, but if the technical and density targets were not included at the time of image capture, there is no way to objectively measure the resolution or the density of the film.
Standards, specifications, and guidelines are descriptions of methods, materials, tolerance, and processes that ensure a desired outcome or result. Standards ensure predictable and consistent results and in the case of preservation microfilm, they ensure high-quality results.
Standards and specifications are established by standards-making bodies such as ANSI, AIIM, ISO and others. Over the years, librarians and archivists have identified the relevant standards that certify preservation quality microforms. In the 1990s, Research Libraries Group (RLG) developed guidelines using the standards as a basis for developing more descriptive procedures and guidelines. Taken together the ANSI, AIIM, ISO standards and the RLG specifications outline a very prescriptive formula for creating, maintaining, storing, and inspecting microforms and for determining their life expectancy if properly prepared and stored.
Additionally, state and federal agencies have similar sets of specifications and guidelines that ensure the long-term stability of agency records of lasting and enduring value.
- James M. Reilly, IPI Storage Guide for Acetate Film (Rochester, NY: Image Permanence Institute, 1993), www.imagepermanenceinstitute.org/shtml_sub/acetguid.pdf; American National Standards Institute/Association for Information and Image Management (ANSI/NISO), ANSI/AIIM MS23 1998—Standard Recommended Practice—Production, Inspection, and Quality Assurance of First-Generation Silver Microforms of Documents, 1998, https://law.resource.org/pub/us/cfr/ibr/001/aimm.ms23.1998.pdf.
- International Organization for Standardization (ISO), ISO 18901:2001—Photography, Imaging Materials—Processed Silver-Gelatin-Type Black-and-White Films—Specifications for Stability.
- American National Standards Institute (ANSI), ANSI IT9.5-1992—Imaging Materials—Ammonia-Processed Diazo Photographic Film—Specifications for Stability.
- American National Standards Institute (ANSI), ANSI IT9.12-1991—Imaging Materials—Processed Vesicular Photographic Film—Specifications for Stability.