The Abbey Newsletter

Volume 16, Number 4
Aug 1992


Storage of Microforms: What are They Doing in the Dark?

ALCTS Preservation Microfilming Committee Program, June 29, 1992, at the ALA Annual Conference in San Francisco

Reported by Carol Unger
Assistant Head, Preservation Section, National Library of Medicine

The program was well attended, with an audience of around 160, and reached many microform reading room managers who do not usually go to preservation meetings. Nancy Elkington of the Research Libraries Group opened the program by reviewing some of the questions librarians have about their microform collections, in particular the "dangers of cohabitation," a reference to the effects of storing together different types of microfilm, and the effects of enclosures on the film. She then introduced Suzanne Dodson, Facilities and Preservation Manager, University of British Columbia Library, who has been actively concerned with microfilm issues for many years, working with ISO/TC 171/Working Group 3 for microfilm standards, and the Canadian General Standards Board Committee on Micrographics and Image Management.

Mrs. Dodson began by recounting her experiences managing the microform collection at UBC, which grew from 70,000 items in 1964 to about four million items today. Over the years microfilm was found to be susceptible to deterioration from a number of causes. In the early 1960s redox blemishes were discovered. In the late 1960s the problem was Kalvar vesicular film, which released hydrogen chloride, causing metal corrosion among other things. In 1984 she learned of an earlier instance of the deterioration of acetate film, which was evidenced by a vinegar smell (from the production of acetic acid). Any such film, if not removed, could affect the rest of the collection, causing it to break down as well. In November 1987, Mrs. Dodson discovered large gold blobs, wavy gold lines, and a "bloom" down the middle of some of her film, some of which was barely 15 years old. She immediately consulted with Robert Mottice at UMI, who early in 1988 referred the problem to the Image Permanence Institute (IPI) and Jim Reilly. IPI had begun to work on this problem, which had been reported by a number of libraries and archives, and which was identified as "mirroring," or "silvering," a form of oxidation of the silver in the film. It was caused by many factors, and Mr. Reilly told her that only the best of conditions would have prevented it in the long run-conditions impossible for most libraries to achieve.

Mrs. Dodson described three types of microform collections: archival, i.e., those meant to last a very long time; disposable, those meant to be superseded and discarded; and middle, the "survivable-for-as-long-as-possible" collection. Most microform reading room collections are of the middle type. The microforms are bought to be part of the library's permanent collection, often at great expense. Film intended for long term storage should be silver halide. Microfilm standards now refer to "permanent value records" rather than "archival records," and rate a film in terms of its LE, or Life Expectancy, rather than in terms of whether it is "archival" or not.

Hazards will vary with the type of film. Diazo film images will fade, and exposure to light causes faster fading. There are different types of formulations for diazo films which means that some will fade faster than others. One test of fifteen diazo films found that the time it took to fade each

film ranged from 3 to 20 hours' exposure to light. Vesicular films also come in different formulations. Current vesicular films do not exhibit the problems of the old Kalvar film. The image is formed by bubbles: if the bubbles are squashed the image is gone. It is also vulnerable to heat, and the extent to which it is resistant to heat depends upon the formulation of that particular film. In tests of some vesicular film the image was lost in 15 minutes' exposure to 158°F. AIIM MS 20 specifies an allowable maximum temperature of 167°F for the film gate of readers, but a quarter of the microfiche readers rated by Library Technology Reports in one of their reviews of this equipment exceeded this temperature-some by many degrees. Vesicular film is also easily scored. Hence dirt in the machine will destroy the image.

Mrs. Dodson feels it is best to avoid storing different film types together, but this is not always practical. The film base is also a consideration, and a library might have nitrate acetate, and polyester base films in its collection. Polyester, which is very stable and durable, is the current best choice.* While most microfilm storage managers are aware of the dangers of nitrate film, fewer are aware that all acetate based films can be expected to deteriorate over time, if kept under poor conditions. In some instances cellulose nitrate film might be in better shape than cellulose acetate film, in which case the latter should be duplicated first, to preserve it. Age and storage history are more important than film types.

Mrs. Dodson then discussed the four most important causes of damage to film. She placed environment as the number one factor and referred to recommended storage conditions listed in ANSI/AIIM IT9. 11. The life of materials can be increased by lowering temperature and humidity. Recent IPI studies show that lowering the temperature from 68° to 37°F increases the life of film 10 times. Lowering the relative humidity from 50% to 20% can increase the life of film 3-10 times. She felt we should educate patrons and library administration to accept a cooler situation. She mentioned an article in the June 1992 Abbey Newsletter describing a kit to monitor environmental conditions. Pollutants which can harm film include peroxides (from paper and wood), chlorine compounds, oxides of nitrogen, sulfur dioxide, hydrogen sulfide (ordinary rubber bands could contain sulfur), impurities in adhesives, gases from paint, ozone produced by photocopiers and certain lamps and electrical equipment, ammonia, smoke, insecticides, dust, abrasive particles, and fungus. She recommended activated charcoal air filters and looped, rather than cut, pile carpeting in reading areas because bits of fibre can be released from a cut pile for a very long time, and these are abrasive. To avoid water damage, she recommended keeping cabinets 6" off the floor. If film does get wet, she advised dumping film, boxes and all, into cold clean water in plastic containers until it can be sent to be professionally cleaned and dried.

The second cause of damage is improper processing of microfilm. She encouraged librarians to be aware of standards for processing of film and to insist that those standards are met.

A third cause of damage described by Mrs. Dodson is storage enclosures. Enclosures should not contain lignin. "Acid-free" is not a guarantee of chemical inertness. Adhesives in envelopes may cause damage. Plastic enclosures should not contain chlorine or plasticizers. Enclosures must pass the Photographic Activity Test (PAT) described in ANSI/AIIM IT9.2. Storage cabinets should have finishes which do not emit harmful gases.

*ANSI IT9.1 gives an LE 500 (500 years) rating to silver halide film on polyester base, but a rating of only LE 100 to silver film on a cellulose triacetate base.

Mrs. Dodson emphasized the importance of proper handling. Machines for viewing and copying microforms must be kept clean to avoid scratches and deposits on the film. Patrons must be educated in careful handling to avoid damage.

The second speaker was Jim Reilly, director of the Image Permanence Institute at the Rochester Institute of Technology, who discussed the Institute's current research on the stability of photographic images, focusing on the materials that microfilm is composed of, i.e., the film base, emulsion and silver, what they are and how they deteriorate. Mr. Reilly first discussed problems with the materials in our existing collections and then turned to how these problems might be prevented in new filming.

Many films in existing collections have acetate bases which chemically decompose, giving off the vinegar smell and ultimately leading to shrinkage and emulsion damage. IPI's research has shown that all cellulosic films are susceptible to deterioration. The rate of deterioration of the film base proceeds gradually until it reaches the autocatalytic point, at which time the rate rapidly increases. Temperature and humidity have a significant impact on how long it takes the film base to reach the autocatalytic point. For instance, film stored at 90° F and 70% RH will reach that point in about 10 years; at 80° and 60% RH, about 20 years; 70° and 30% RH, about 100 years. Cool or cold storage is highly desirable. For instance, the latest edition of ANSVAIIM IT9. 11 recommends a maximum temperature of 72° and 20-30% RH for black and white film.

Silver image problems have arisen because of oxidation which may cause redox blemishes, silver mirroring or overall fading. The causes of silver image deterioration are airborne contaminants such as generalized air pollution, paint vapors, building materials, and chemicals in enclosures such as boxes and jackets. It is very difficult to pinpoint specific causes when redox blemishes are found in a collection. High relative humidity is an accelerating factor. Some film degradation is likely to be found in any older microform collection. Reilly reiterated that control of temperature and humidity, replacement of damaging enclosures and air filtration will help to protect existing collections. IPI has performed research in the area of enclosures and has developed the Photographic Activity Test (PAT) now specified by ANSI Standard IT9.2-1991. The PAT indicates whether the enclosure will harm silver. It can also be used to test inks, adhesives and labels. IPI has recently developed a PAT for diazo film. Again he stressed that the label "acid-free" is not sufficient: a film enclosure should pass the PAT. In new filming, he discussed the importance of using film that has a long life span. Polyester film base has a life expectancy at least five times longer than that of acetate stored under similar conditions.

Protecting the silver image from redox or mirroring is possible with a new technique developed and tested by IPI. This is the IPI Silverlock™ Polysulfide Treatment. The polysulfide treatment may be applied during or after processing, but is not currently recommended for film older than 10 years. The treatment works by chemically reacting with silver to form silver sulfide. However, good environmental conditions should still be maintained for storage. Silverlock is available from IPI and some vendors such as MAPS and UMI. IPI is now researching the effects of polysulfide treatment on film with some redox blemishes and with age-weakened gelatin.

Mr. Reilly stated that IPI's research on color microfilm has led them to conclude that color microfilm is a viable preservation option. There are two types of color film available now which may be considered. The image dyes in Cibachrome silver dye bleach microfilm (now known as Ilfochrome color micrographic film) should remain stable in dark conditions for 200-300 years at room temperature. Chromogenic color film, which is currently used in motion picture film, requires cold storage to maintain the same degree of dye stability as Cibachrome.

Abbreviations used:

AIIM - Association for Information and Image Management ALA - American Library Association ANSI - American National Standards Institute MAPS - MicrogrAphic Preservation Service UMI - University Microfilms International

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