Preservation Microfilm
Preservation microfilm is a microphotographic reproduction of an information resource originally available in paper or other format. This reproduction consists of microimages that are created in a silver-gelatin emulsion applied to a polyester film base. A preservation microfilm should be a camera original film (i.e., "first generation") with the microimages appearing in negative polarity.
The film product, consisting of the base and emulsion, is expected to exist in perpetuity through its manufacture, use, processing, housing, and storage in accordance with established standards and recommended practices without degradation. Applying the term "preservation" to a microform in general carries the expectation that the information sources available for reformatting are as complete as possible and presented in a coherent arrangement; that the physical materials of the film product are of a recognized and established stability; and that efforts need not be undertaken to recreate a microform of the same information source. A preservation microfilm should include explanatory information so that, when a copy is made from the original film, there is easier access and identification of information appearing in the microphotographic reproduction.
Preservation Microfilm*
*Microfilm rolls are stored in single reel storage boxes found on pages 21 and 22. All rolls should have wrappers placed around them for identity purposes. These wrappers are displayed on pages 24 and 25.
Microfilm, Negative, 35 mm, roll:
on acetate base up to approximately 1980, on polyester base after 1980
First Generation = Preservation Master Negative - stored on a core
(This film is exposed in the camera and then developed in a processor as a roll of film with a negative image. This is the most significant film for preservation purposes.)
Second Generation = Direct Duplicate or Printing Master or Duplicate Negative - stored on a reel
(This film is copied from the Preservation Master Negative and is still a roll of film with a negative image.)
Microfilm, Positive, 35 mm, roll:
on acetate base up to approximately 1980, on polyester base after 1980
Third Generation = Service Copy or Use Copy or Distribution Copy - stored on a reel
(This film is copied from the Direct Duplicate, processed and now has a positive image on a roll of film. It is for use in the Reading Rooms, as Loan Copies or as Sale Copies, subject to Copyright restrictions, from the Photoduplication Service.)
Microfiche*
on acetate base up to approximately 1980, on polyester base after 1980
*Standard size microfiche sheets are stored in the 4"x 6" paper envelopes displayed on page 6.
The Microfiche Service Copy is a third generation positive film cut into single sheets with multiple images (one or many) in a proscribed sequence comprised of a standard number of images. The number of images generally depends on the reduction ratio, but outside dimensions of the microfiche sheet are one standard size that will fit into microfiche readers in the LC Reading Rooms.
