007  Physical Description Fixed Field (Microform) (R)

Microform. The item is a microform, which is a generic term for any medium, transparent or opaque, bearing microimages. A microimage is a unit (e.g., a page) of textual, graphic, or computer-generated material that is contained on aperture cards, microfiche, microfilm, microopaques, or other microformats and that is too small to be read without magnification. A microform may be reproductions of existing textual or graphic materials or they may be original publications.

Aperture card. A card with one or more rectangular opening(s), or aperture(s), specifically prepared for the mounting or insertion of a piece of photographic film containing one or more microimage(s). The cards are usually EAM (Electrical Accounting Machine) punched cards, commonly known as IBM cards, that are standardized for use in card-handling machines. Such cards contain only one aperture and most frequently have only one microimage.

Microfilm cartridge. A microfilm cartridge consists of a strip of photographic film wound onto a single core (or hub), housed in a protective container. Microfilm cartridges require reading equipment (readers and reader-printers) that is specifically adapted for their use. Normally, the end of the film is left free for threading into such equipment. Common film lengths, widths, and reduction ratios are the same as those of microfilm reels.

Microfilm cassette. A microfilm cassette is analogous to a sound tape cassette. It consists of a strip of photographic film wound onto a double core, housed in a protective container. Microfilm cassettes require reading equipment (readers and reader-printers) that is specifically adapted for their use. Because they are double-cored, they are not threaded when used in such readers and reader-printers. Usual film lengths are 100 feet (approximately 30 m) or less. Common film width is 16 mm and usual reduction ratios are those of microfilm reels and cartridges.

Microfilm reel. A microfilm reel consists of a strip of photographic film wound onto an unenclosed flanged holder (or reel). Microfilm reels require manual threading when used in readers and reader-printers and require equipment that is adapted for their use. Film lengths are usually 100 feet (approximately 30 m) or less. For microimages produced by filming textual and graphic materials, the most common film widths are 35 mm and 16 mm and reduction ratios commonly range from about 10:1 to about 20:1. Sixteen millimeter film with effective ratios of either 24:1 or 48:1 is most often used for COM (Computer-Output-Microfilm) microimages.

Microfiche. A microfiche is a transparent sheet of photographic film containing microimages arranged in a grid pattern (a two-dimensional array) and having a heading that contains identifying information in text that is large enough to be read without magnification. Grid patterns vary with reduction ratios.

Microfiches are grouped in five ranges of reduction ratios: low reduction (ratios up to and including 15:1), normal reduction (ratios greater than 15:1 up to and including 30:1), high reduction (ratios greater than 30:1 up to and including 60:1), very high reduction (ratios greater than 60:1 up to and including 90:1), and ultrahigh reduction (ratios greater than 90:1).

The most common microfiche are made by filming textual or graphic material at a reduction ratio of approximately 24:1. Such microfiche are 105 mm high and 148 mm wide (approximately 4 x 6 inches) and have a grid pattern that accommodates 98 microimages made from documents that are no more than 11 inches high and 8 1/2 inches wide. The heading area is the width of one row and is found directly above the first row of microimages.

The most common COM (Computer-Output-Microfilm) microfiche are made by recording computer-generated data at an effective reduction ratio of 48:1 on a 105 mm x 148 mm sheet of film. Such microfiche have a grid pattern of 15 rows and 18 columns, comprising 270 microimages. The heading area is the width of one row and is found directly above the first row of microimages.

Microfiche made at ultrahigh ratios are commonly called ultrafiche. Ratios and grid patterns have not been standardized for these microfiche and differ according to application and method for production.

Microfiche cassette. A microfiche cassette is a cassette containing uncut microfiches.

Microopaque. A microopaque is a sheet of opaque material bearing a number of microimages arranged in a two-dimensional array. Microopaques resemble microfiche. Common dimensions are 3 x 5 inches and 6 x 9 inches. Common reduction ratios are approximately 24:1 or 20:1. Microopaques usually have identifying information in text that is large enough to read without magnification.

Microfilm slip. A microfilm slip is short strip of microfilm cut from a roll.

Microfilm roll. A microfilm roll is a wound length of microfilm not on a reel, cartridge, etc.

Unspecified. A microform for which the special material designation is not specified.

Other. A type of microform for which none of the other codes is appropriate. Some microform types that use code z include:

• microchip - A sheet of photographic film of very small dimensions.
• microdot - A minuscule piece of photographic film with ultrahigh reduction ratio.
• microform scroll - A roll of unusually wide photographic film.

Positive. Indicates a positive microform in which lines and characters appear dark against a light background. Microopaques are always recorded as code a.

Negative. Indicates a negative microform in which lines and characters appear light against a dark background.

Mixed polarity. Indicates a microform with mixed polarity, i.e., a microform that is a mixture of positive and negative images.

Unknown. Indicates a microform the polarity of which is not known. (Some colored negatives may appear to be positive if the colors of the original are not known.)

8 mm. Indicates the width of the microfilm in millimeters.

16 mm. Indicates the width of the microfilm in millimeters.

35 mm. Indicates the width of the microfilm in millimeters.

70 mm. Indicates the width of the microfilm in millimeters.

105 mm. Indicates the width of the microfilm in millimeters.

3 × 5 in. (8 × 13 cm). The height and width of the microfiche or microopaque in inches or centimeters.

4 × 6 in. (11 × 15 cm). The height and width of the microfiche or microopaque in inches or centimeters.

6 × 9 in. (16 × 23 cm). The height and width of the microfiche or microopaque in inches or centimeters.

3 1/4 × 7 3/8 in. (9 × 19 cm). The height and width of an aperture card in inches or centimeters.

Unknown. The dimensions are not known.

Other. Dimensions for which none of the other codes is appropriate.

Low reduction ratio. A reduction ratio less than 16:1 (that is, less than 16x or less than 016).

Normal reduction. A reduction ratio between 16:1 and 30:1 (that is, between 16x and 30x or between 016 and 030).

High reduction. A reduction ratio between 31:1 and 60:1 (that is, between 31x and 60x or between 031 and 060).

Very high reduction. A reduction ratio between 61:1 and 90:1 (that is, between 61x and 90x or between 061 and 090).

Ultra high reduction. A reduction ratio over 90:1 (that is, over 90x or over 090).

Unknown. A reduction ratio that is not known.

Reduction ratio varies. Not all parts of the microform have the same reduction ratio (e.g., the contents of two books may be microfilmed onto one piece of film; the type face on the books may differ, so that one of the books may be filmed at a 14:1 ratio and the other at a 18:1 ratio).

The second, third, and fourth character positions of subfield ǂf (007/06-08) represent the reduction ratio itself, the number specifying the reduction ratio for the microform, recorded as three digits. If you are entering a ratio that is under 100, enter leading zeros for the second and/or third positions (e.g., 008, 015, 048). If you do not enter the specific ratios, a hyphen is used for any unknown portion of the reduction ratio (e.g., 03-, 1--). If no specific reduction ratio is recorded, enter a hyphen in each of the second, third, and fourth positions (that is, ---).

Generally, the specific reduction ratio should be recorded when it is ultra high (code e in the first character position of subfield ǂf). If the ratio is not ultra high, recording the specific ratio is less essential and therefore optional, in which case three hyphens should be entered.

Black-and-white. The microform image is in black-and-white (usually black-and-transparent). Includes only one color or hue other than black, for example, blue-and-white (blue-and-transparent). Always used for microopaques.

Multicolored. The microform image has more than one color.

Mixed. The microform is a combination of one-color and multicolored images.

Unknown. The color of the microform is not known.

Other. A microform coloration for which none of the other codes is appropriate.

Silver halide. Silver halide emulsion is a compound of silver and halogens. Silver halide microforms are always appear black-and-white (black-and-transparent). Most commercial microforms are silver halide.

Diazo. Diazo emulsion is sensitized layers composed of diazonium salts that react with couplers to form dye images. The color of the image is determined by the composition of the diazonium compound as well as the couplers used in the process and may be black, violet, or another color.

Vesicular. Vesicular emulsion describes films in which a light-sensitive component is suspended in a plastic layer. On exposure, the component creates optical vesicles (bubbles) in the layers. These bubbles form the latent image. The latent image becomes visible and fixed by heating the plastic layer and then allowing it to cool. Vesicular films are commonly blue or beige in color. They do not appear to have much contrast (very high density) until projected in a microform reader.

Mixed emulsion. A microfilm may have slices of film with one type of emulsion and other slices of film with another type of emulsion.

Not applicable. The microform does not have emulsion on film. Use for microopaques. Microopaques are not on film.

Unknown. The type of emulsion on the film is not known.

Other. A type of emulsion for which none of the other codes is appropriate.

First generation (master). The first generation is the camera master or COM recorder master. Use for all master films made on archival stock in accordance with archival production standards and given archival storage under relevant ISO standards.

Printing master. A printing master is a microform of any generation employed mainly for the production of other microforms. Used for all masters not manufactured, produced, and stored in accordance with archival standards.

Service copy. A service copy is a microform made from another microform that is intended primarily for use rather than for production of other microforms. Most microforms used in libraries are service copies. Always used for microopaques.

Mixed generation. A microform copy that is made up of a combination of generations of film.

Unknown. A microform for which the generation aspect is not known.

Safety base, undetermined. A safety base film whose type has not been identified.

Safety base, acetate undetermined. An acetate safety base film whose exact type cannot be determined (i.e., if you do not know whether the type is diacetate or triacetate).

Safety base, diacetate. A cellulose diacetate film base. Introduced before World War I for home movies, diacetate base was more expensive and unpredictable than nitrate base and so failed to gain acceptance in professional 35 mm film production. Diacetate film base was at times used for microfilming of documents.

Nitrate base. A cellulose nitrate film. Cellulose nitrate support or base was used in the manufacture of 35 mm film (and some 17.5 mm film) until 1951. Nitrate base film is no longer manufactured. Nitrate film is highly flammable. It does not meet the requirements for safety base film. Nitrate film base was at times used for microfilming of documents.

Mixed base (nitrate and safety). A combination of nitrate base and safety base film. The use of mixed bases, spliced together, can be found in microforms from the early 1950s.

Not applicable. A microform item that does not have a film base. Such items are primarily microforms on a reflective rather than transparent base. Microopaques (also called microcards or microprints) are examples of microforms not produced on a film base. Use code n for microopaques.

Safety base, polyester. A film base made of a synthetic resin (e.g., ESTAR Base). During the 1980s, it became the most widely used base for microfilming of source documents.

Safety base, mixed. Spliced together safety base films, with no nitrate film. Do not use if the spliced film is nitrate based.

Safety base, triacetate. A cellulose triacetate film base. Cellulose triacetate is a high acetal compound with very low flammability and slow burning characteristics. From 1951, triacetate has been used for professional as well as amateur produced moving image film. It has also been used at times for microfilming of documents.

Unknown. The base of film of the microform is not known.

Other. A film base for which none of the other codes is appropriate.