Microfilm may not enter our spheres of interaction as often as once it did, but it remains a reliable and long-lasting archival medium. There are some exceptions to this rule, and any material may become compromised if not handled correctly. If you’ve got a microfilm collection that you’re learning how to maintain, take heed to how your storage conditions will affect the longevity of your materials.
Most of what we talk about in this blog is going to center around the types of deterioration you may encounter and how the resilience of microfilm correlates directly with your storage environment’s humidity, average temperature, and air quality. When these three factors are controlled, you really can rely on your microfilm to last centuries.
Microfilm Terminology Refresh
- What is microfilm? Microfilm is a medium by which you can store high-density visual media in a small-scale format, stable and long-lasting, for archival purposes. Images are reduced, captured side-by-side on film, and stored in reels. Photographic film consists of several layers. Those of primary concern for preservation are the plastic film base and the photographic emulsion layer. The base is the flexible plastic that forms the structure of the film. “The emulsion layer is the part of the film that actually contains, or holds, the image.” (Selle 2003, 2) Microfilm emulsions have a finer grain than other films, engineered to capture miniscule text detail at high reduction ratios.
- How is it created? Blank microfilm stock is loaded into a specialized microfilm camera. Materials are placed in a media cradle below the camera and photographed. The film is then developed and usually duplicated to create separate master and service copies.
- What are the common varieties of microfilm bases? Cellulose Nitrate was used for early commercial films through the first half of the 20th century. Nitrate base microfilm is rare. Cellulose Acetate (also called Cellulose Triacetate or Safety Film) became the standard base for all kinds of film in the 1950s. Polyester (also called Polyethylene or PET) replaced acetate as the standard base for preservation microfilm in the 1980s. Today, only Polyester is considered chemically stable for archival purposes.
- What are the common varieties of film emulsions? Silver Halide, Diazo, and Vesicular are three common emulsions used to generate images upon a film base. Silver Halide is the most secure and long lasting of the three. The first generation camera negative, the archival master, is always Silver Halide film. Diazo and Vesicular emulsions are inexpensive alternatives to Silver Halide used for duplication films but neither are considered archival quality. The Diazo chemical process is unstable in the presence of light and will fade easily. With frequent or heavy use, it can even be affected by the lights of microfilm readers. Vesicular film images are created when heat ruptures dye vesicles in the film emulsion. The processed film remains sensitive to heat.
- What are the ANSI/AIIM guidelines? ANSI is the American National Standards Institute. ANSI codifies standards proposed by a host of expert groups. AIIM is the Association for Intelligent Information Management, the group that oversees technical microfilm processing standards in the United States.
- What are the RLG guidelines? The Research Libraries Group established a community of practice around preservation in libraries and archives. Collaboration among research libraries led to the adoption of microfilming standards for newspapers, brittle books, and other archival materials.
RLG was absorbed into OCLC in 2006, but the RLG guidelines remain the microfilming standard for cultural heritage preservation. RLG preservation guidelines recommend 35mm silver halide polyester base microfilm for master and service copies.
The Sour Elephant in the Room: Acetate Film
We aren’t going to talk about Nitrate film in this blog (notorious for its tendency to spontaneously combust at sustained high temperatures), but it’s worth noting that Nitrate film shares many of the same risks for disease and deterioration as Acetate. If microfilm has a bad reputation, it’s almost certainly because of the stories surrounding Nitrate and Acetate films.
While all film types can suffer from issues with humidity, temperature, and pollutants, Acetate is especially sensitive. Vinegar Syndrome occurs when “chemically, the cellulose acetate composition changes, causing acetyl groups to break from the chemical chain.” (Selle 2003, 2). The acetic acid that is released begins inside the plastic initially before eventually rising to the surface. (Reilly 1993, 10). You can use A-D strips, produced by the Image Permanence Institute, to determine the severity of acetate deterioration. You can also contact Backstage for a small test kit if you only have need of a few strips. While a vinegar smell is a clear sign of deterioration starting, the intensity of smell may not necessarily correlate with the degree of damage being done. Once a certain amount of acid has developed within the base, the rate of deterioration will exponentially increase in an autocatalytic reaction.
What happens when the base starts to deteriorate? Film may become brittle, shrink, or bubble up – all issues starting with the film base that render the emulsion layer unusable by different mechanisms. The onset of Vinegar Syndrome, however, does not necessarily herald the certain loss of your materials. There are ways to slow it down. Above all, duplicating your preservation copies of microfilm to a Polyester base with Silver Halide emulsion, or even just digitizing it, before it begins to seriously degrade is the safest course of action.
Your Storage Environment Is Your First Defense
The IPI Storage Guide for Acetate Film describes the connection between temperature and humidity, and how these two factors particularly will greatly influence how long Acetate film survives. There are few resources that discuss how these factors can affect Polyester, but this is largely due to the current research and shared experience that Polyester base is more resilient than its predecessors. While Polyester base is stable, the emulsion layer can still be susceptible to the following problems.
Mold: High relative humidity (RH) for even short lengths of time can negatively affect your microfilm. “Any time the ambient RH remains above 70% RH or so for several days, mold growth is possible.” (Reilly 1993, 17) Prevention remains the best practice and your microfilm should be consistently stored in a moderately dry environment, between 30% and 50% RH.
Accidents can still happen, such as flooding or faulty HVACs, and there are multiple cases of libraries inheriting microfilm that hadn’t been stored in optimal conditions for one reason or another. These days, companies exist that can help remediate the damage that’s been done and prevent deterioration. The sooner you can respond, the better!
Pollutants: It is possible for images to fade. The standards for microfilm storage typically recommend having some sort of air filtration. Managing the presence of oxidizing agents such as ozone, peroxides, and nitrogen and sulfur oxides (NOx and SOx) can help reduce the impact of oxidation on silver images. This factor goes hand in hand with relative humidity, making humidity management your greatest concern when it comes to storing film.
Redox, or reduction-oxidation, is a well-known phenomenon that directly correlates to the presence of pollutants and is an issue exacerbated by humid environments. Pink, orange, or yellow spots can be seen when “viewed in transmitted light.” These are the result of metallic silver particles in the image emulsion oxidizing, then migrating as silver ions along the silver filament structure of the image to gather in pockets and reduce to colloidal silver in rust-colored spots.
Packing your microfilm tightly helps to prevent redox spots. Acid-free wraps and string ties can keep film tightly wrapped on its reel. SilverLock polysulfide treatment is an effective chemical guard against redox, converting roughly 65% of the metallic silver to more stable silver sulfides, which interrupts the ionic migration of the remaining silver. Polysulfide treatment is best performed when film is developed, but it can be applied to existing film.
Redox is not reversible. There is no way to restore the information that has been obscured by redox blemishes, but you can duplicate the film to preserve what remains onto a stable base and emulsion layer.
Recommendations for Storage and Quality Assurance
Another factor that can damage your microfilm is a pretty obvious one – physical damage. Microfilm that isn’t stored in the correct enclosures is susceptible to dust, pest problems that might crop up, or the simple wear-and-tear of being handled. This, and all the reasons stated previously, is why your microfilm should be stored with intentionality and care.
Make sure to review your film according to a quality assurance schedule. Many of the diseases mentioned in this blog are issues that can spread or are directly correlated to storage problems; regular check-ups will help you catch unseen issues with your storage environment and monitor the overall health of your film.
“An important aspect of film storage is regular film inspection. No matter how carefully the film was manufactured and processed, and no matter how carefully the storage facility was constructed, or the storage enclosures chosen, there is a possibility that something may go awry.”
(Gwinn 1996, 223)
Your guide will be the ANSI/AIIM MS45-1990 Recommended Practice for Inspection of Stored Silver-Gelatin Microforms for Evidence of Deterioration. Over the course of two-year periods, you should make sure that you have inspected film from each drawer or cabinet for the following:
- Mold or fungus
- Discoloration
- Changes in film density
- Redox blemishes
In Acetate collections, also check for:
- Vinegar odor
- Film curl
- Excessive brittleness
- Emulsion separation from base
- Adhesion of film to itself
Key Takeaways
Managing your storage environment will nearly eliminate the opportunities for your microfilm to deteriorate. Acetate film is the exception; before, or when, your microfilm enters a state of deterioration, duplicate it to new polyester film. Proactive maintenance will secure the longevity of your materials.
There’s a lot of information here, and it may help to have an abbreviated breakdown of the key considerations for microfilm storage based on how we have modeled our own storage facility.
- Store in a temperature-controlled environment. The temperature should not exceed 60°F. Control moisture and keep humidity below 50%, with ideal conditions of around 40%.
- Store your records in a dark place and limit exposure to light. Keep your storage facility clean.
- Don’t paint rooms without removing your microfilm first.
- Microfilm storage boxes described in the IPI guide “must meet the general requirements outlined in ANSI Standard I9.2-1991 and must pass the ANSI Photographic Activity Test (ANSI Standard IT9.16-1993)” (Gwinn 1996, 223). The Library of Congress maintains a highly detailed list of the supplies required to store archival microfilm.
If you’d like to know more about microfilm or have questions about evaluating the health of your microfilm collection, call us at 1.800.288.1265, visit us online at www.bslw.com, or send an email to info@bslw.com.
References
“FilmCare.org.” n.d. Www.filmcare.org. Accessed March 14, 2024. https://www.filmcare.org/vd_redoxblemishes.php.
Gwinn, Nancy E, Lisa L Fox, and Association Of Research Libraries. 1996. Preservation Microfilming : A Guide for Librarians and Archivists. Chicago: American Library Association.
“Preserving Microforms | Naa.gov.au.” 2024. Naa.gov.au. 2024. https://www.naa.gov.au/information-management/storing-and-preserving-information/preserving-information/preserving-microforms.
Reilly, James M. IPI Storage Guide for Acetate Film. Rochester, NY: Rochester Institute of Technology, 1993. https://s3.cad.rit.edu/ipi-assets/publications/acetate_guide.pdf
Selle, Tyler. 2003. Acetate Microfilm, publication no. 15: 1–6. https://www.archives.nysed.gov/sites/archives/files/mr_pub15.pdf.
