Layman's guide to microfilm

Microfilm Terminology FAQ

1. Question: What is Microfilm made from?

Answer:

When talking about microfilm construction, we’re going to be interested in the film base and the emulsion. What follows are the most common forms of both, although you should bear in mind that there are some other varieties if you’re trying to identify film in your collection. Backstage prefers to use polyester and silver halide for its projects due to its stability and reliability.

The film base is the actual reel of film upon which images are produced.

  • Cellulose Nitrate: Used in film and photography between 1880s and the early 1950s. Its use was discontinued due to its flammability and rate of deterioration. While its life expectancy (LE) can be up to 500 years1 it is autocatalytic once deterioration begins and the stages therein are likely to destroy the film past readability or the ability to duplicate.
  • Acetate: Used between 1920s and 1980s, acetate became the “answer” to nitrate bases. However, it is autocatalytic like its predecessor. Deterioration is easily identified by its vinegary odor, also known as vinegar syndrome. Acetate film can survive for about one hundred years if stored correctly.2 
  • Polyester: Used since the 1980s, polyester is much more durable, boasting a LE of 500 years, and it is chemically stable.

NEDCC3 has an excellent resource that can assist in identifying the types of microfilm in your collection. 

Emulsion is the substance that allows for images to appear on the film base.

  • Silver Halide: The archival standard of ANSI and AIIM guidelines, silver halide emulsion is the most reliable when it comes to accurately representing an original source material. Mostly used in creating archival and print masters with a LE of up to 500 years.
  • Diazo: Sensitive to light, the LE of Diazo is closer to 100 years. Where silver halide is distinctive with a dull and shiny side, diazo is identifiable with its shininess on both sides of the film.

2. Question: Can microfilm with an unstable base, such as nitrate or acetate, be duplicated onto polyester? 

Answer:

Yes – however, Backstage does not work with cellulose nitrate film due to its instability. We regularly work with clients to identify acetate film and slow the process of deterioration. We have worked with film suffering from vinegar syndrome and been able to duplicate several collections that would have otherwise been lost!

3. Question: What are microfilm generations, masters, and copies, and how does polarity relate?

Answer:

A microform will exist in either positive or negative polarity. “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.”2  The generation refers to how many times the original resource has been duplicated. Standards recommend three generations of microfilm to preserve the images in pristine condition while providing access to patrons and distribution to other institutions and remote researchers.

  • Archival Master: The first generation, known as the archival master, is the film used in the microfilm camera. It may also be referred to as the camera master, camera negative, or master negative. After processing, these original images are stored for preservation purposes. This is filmed in negative polarity.
  • Print Master: The second generation is the print master, a film negative duplicated from the archival master. The print master is used to create service copies, protecting the archival master from machine wear. It is stored in a separate location from the archival master to mitigate risks. This is also filmed in negative polarity.
  • Service Copy: The third generation, the service copy, is a positive image duplicated from the print master. This film is made accessible to end users who may view it and capture digital images of the content using a microfilm reader. Depending on distribution plans and user needs, extra service copies may be made when the film is initially processed or at a later date as replacements are needed or inter-library loan (ILL) and other resource-sharing requests are made. 

4. Question: How long does microfilm last if we’re considering it as a preservation solution for our collection?

Answer:

Using silver halide on polyester film, and assuming you are storing your archival masters in correct conditions, there’s no reason why it shouldn’t have a LE of 500 years. You can add an additional level of security if you ask Backstage to apply a Silverloock® Polysulfide treatment which converts the metallic silver remaining in the emulsion to stable silver sulfides. This helps prevent patches of fading and keeps the film free of the common effects of atmospheric pollutants.

Remember that microfilm can be viewed with nothing more than a light box and magnifying device, and digitized files can be created from microfilm to couple accessibility and preservation to your original materials.

1 Vitale, Tim. “History, Science, and Storage of Cellulose Acetate Film Base.” cool.culturalheritage.com, June 5, 2009. https://cool.culturalheritage.org/videopreservation/library/history_science_storage_of_acetate_base_film_16b.pdf.

“3. Microform Terminology”, American Library Association, August 20, 2013. http://www.ala.org/alcts/resources/collect/serials/microforms03 (Accessed April 4, 2022) Document ID: cfb6a4f6-8f86-4716-8ed3-c9f80941f9a8

3 Fischer, Monique. “5.1 A Short Guide to Film Base Photographic Materials: Identification, Care, and Duplication.” Northeast Document Conservation Center, 2020. https://www.nedcc.org/free-resources/preservation-leaflets/5.-photographs/5.1-a-short-guide-to-film-base-photographic-materials-identification,-care,-and-duplication.

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