Microform is a general term for anything containing microimages. There are a number of different microforms that serve various records management needs. Factors which must be considered in to determine which microform will be most useful include:
- Frequency and volume of data retrieval
- Frequency that paper copies are required
- Frequency of file updating
- Retrieval speed requirements
- What locations need information
- Security and file integrity needs
- System compatibility
- Status of active or inactive data
Roll microfilm is the least expensive microform to produce and duplicate and it is the most widely used.
Microfilm comes in rolls 100 feet long (215 feet for thin film). Once filming is completed, adding a new frame (page) somewhere in the middle of the film is difficult. If files are added to frequently, microfilm is not the best option. Microfilm can be set up so that users can move to bookmarks (called "blips") quickly anywhere on the film reel. This does require film reader machines to utilize the "blip" system, however.
Microfiche or "fiche" are made from 105 mm film divided into cards. Each fiche contains multiple microimages in a grid pattern. Reduced 24 times (24X), 98 pages can be put on one fiche. At 48X, 270 pages will fit. Documents may be exposed on microfiche in a variety of styles. Identification information placed at the top of the fiche in a title area can be easily read without magnification. Each fiche holds approximately 90 pages of information. Microfiche are somewhat easier to handle and information can be found quickly. They allow additions more easily than microfilm because extra fiche can be filed behind the first, keeping data intact. The Archives no longer has equipment for microfiche duplication, except for converting to a digital format.
Cine: Pages or frames are arranged as on motion picture film, with writing perpendicular to the edges of the film.
Comic: Pages and frames are arranged with writing parallel to the edges of the film.
Title card: A printed sign with a large letter or number on it is photographed between separate file segments or sets of pages.
The following are not offered by the Archives, and are here for reference:
Bar code lines: A special camera exposes progressively larger lines between frames of microfilm. A scale, which can be attached to an ordinary reader, is used to index the lines. This system is for general indexing but it is not accurate to the frame.
Photo-optical binary code: A special camera records numbered codes on microfilm. A special retrieval machine locates the desired number code. The photo-optical binary code system is inferior to the blip system because each code requires a whole frame of microfilm which makes it impractical to index individual frames of information. This method can only be used for general indexing.
Image counter (blips): Blips are marks microfilmed below the exposed frames along the length of the film with a special camera. With this method, frames can be retrieved quickly by using a machine equipped with a push-button retrieval system that counts the blips electronically.
Silver-based film: The film used in the camera is silver-based film. Because it has an extremely long life expectancy, it is also used as a master storage copy. The emulsion is easily scratched, so it is not ideal as a working copy.
Diazo: Diazo is used by the Archives to make working copies from the silver halide original. The diazo copies maintain the image of the original film. Diazo film is scratch-resistant and durable, although it has a shorter life expectancy than the master.
Vesicular: This is another type of working copy film. It is not used by the Archives. Vesicular copies reverse the film of the original, so they have natural-appearing images.
Documents with permanent retention periods must be reformatted on the most stable medium possible if they are to be used into the indefinite future. Silver halide film can last more than 500 years if it is manufactured, processed, and stored properly. Diazo copies last approximately 20-50 years. When choosing a microfilm system, it is important to decide ahead of time if the film must be of archival quality.