MICROFILM: STILL MY TOP CHOICE FOR A PRESERVATION MEDIUM
Suzanne Cates Dodson
Vancouver, British Columbia, Canada
Microfilm seems, to many, outdated and behind the times. In our computer-driven society electronic imaging must, surely, be the way to go if one needs to preserve information for posterity. I disagree, and here's why microfilm is still my choice of preservation medium for any information that needs to be around for a long, long time.
Microfilm possesses two simple advantages over most other media used for recording information: it is long-lived and it is readable by humans. These are pretty basic attributes but they are also crucial. Information retained in an electronic format is only retrievable when you have the appropriate hardware and software to do the retrieving, and few will argue that all the equipment we have today will still be around tomorrow. Even if appropriate equipment is available in ten or twenty years the electronic medium chosen to carry some specific information could well, by then, have deteriorated to the point of being unusable. Unfortunately, we have many examples of this kind to reflect upon.
Proponents of electronic imaging make keeping up with advancing technology sound easy. One simply "refreshes" the files, transferring them to the latest version in order to assure that the data are not lost. I worked in a large university library and the prospect of transferring our collections from one format to a new one was daunting. If your collection consists of a small number of files perhaps you could contemplate redoing them every few years, but for collections of any large size it's close to impossible. Furthermore, I suspect that in many cases people would forget to do anything until it was too late.
Microfilm, on the other hand, is a medium proven capable of lasting in excess of one thousand years, given reasonable care. And, equally importantly, the information on microfilm can, in a pinch, be retrieved with an instrument that has been around for centuries and will continue to exist for as long as humanity exists - the magnifying glass.
Microfilm is available in a number of types and it's important to differentiate among these. Each type suits the purpose for which it was manufactured, but I have found that many people fail to understand the differences between film types and as a result may choose the wrong film for their application. Since you cannot always rely on vendors to be as knowledgeable about which film type is the best choice for your application as you might expect, it's important for you, as a consumer, to be educated in the characteristics of each type. By choosing the appropriate film, and by being aware of the hazards to the longevity of each type of film the users can assure themselves of a successful outcome.
Technical Report for Information and Image Management - Preservation of Microforms in an Active Environment - Guideline, ANSI/AIIM TR13-1998, of which I was the primary author, is published by the Association for Information and Image Management International. It gives (I hope) the reader the basic information needed to make an informed choice of which film type to use and how to look after it. The following information is taken from that report and I would urge anyone responsible for a microfilm collection to buy a copy, because there is a great deal of additional information in it which isn't repeated here. I can assure you that I have no ulterior motive in suggesting this because I have never received, nor will I ever receive, one cent for the work I put into the report. People who work on standards do so because of their interest in the subjects, not for any material gain!
Three types of microfilm are currently most commonly in use: silver halide, diazo, and vesicular. Of these, only silver halide is considered by the preservation community to be suitable for preservation purposes. Diazo and vesicular films can be used for the retention of records for varying periods of time but only silver halide film on a polyester base, processed and stored in accordance with the existing standards, has been proven to be capable of lasting more than 1,000 years. In the past cellulose acetate was used as a base for microfilm but since the mid-1950s nearly all microfilm is on a polyester base, which contributes to the durability and longevity of the film. "The longest accelerated aging studies to date on polyester base films have now been completed . Under reasonable storage conditions, film life greater than 1,000 years is expected." (Reilly, et al, New Approaches, p.ii.)
In considering the three film types (and assuming that they are all on polyester bases) only silver halide, as I have already mentioned, is suitable for long term preservation of information. Most films used to create a microfilm original (the camera films) are silver halide films. In addition, duplicates of the original film can be made using silver halide film, although many prefer to use less expensive diazo or vesicular films for working copies. Silver halide film is quite resistant to heat and to light, unlike its two main alternatives, as I've noted below. Many standards governing the manufacture, processing, and storage of silver halide film exist, which means that the purchaser of this film type can be assured that if the standards have been adhered to the film will meet expectations. ANSI/AIIM TR13 includes a list of the most important standards. It is important to note that standards are always evolving, and although those cited in TR13 were current in 1998, one should check for the current version of any standard, as well as for new ones which may have appeared since.
The two other film types often used are diazo and vesicular. Each of these films has its strengths and weaknesses and each can be a wise choice for an application where the records are not expected to be kept for a long time, or where a duplicate working copy is needed. These films are usually less expensive than silver halide film so using them makes sense where the films are expected to be expendable.
The main weakness of diazo film is that the images on this film fade. Depending upon the type of diazo you use the rate of fade varies considerably. In one test, the time in which individual diazo films from different manufacturers faded to the point of being unusable when exposed to the light of a reader ranged from 30 hours to 3 hours (Jones, p.12.). Diazo films are manufactured for different purposes but in my experience when they used diazo films, micropublishers' choices often reflected an ignorance of the appropriate type for their specific application. Since most consumers have no idea of what they should be getting the result can be disappointing, if not disastrous. To further compound the problem, diazo films can vary in colour from blue to black, and some hapless customers have undoubtedly thought they had silver halide film when in fact they had black diazo. (A quick check of both sides of a film can let you readily distinguish between the two: silver halide film has one shiny side and one dull side (emulsion), whereas black diazo is shiny on both sides.)
Vesicular film gets its name from the fact that the image is made up of many tiny bubbles (or vesicles). Its two main drawbacks are that it is sensitive to pressure damage and it can be easily scored by dirt on a reader (a special hazard for roll film) leaving streaks or what looks like scratches where the image used to be. Also, if it gets too hot the bubbles burst and the image is gone. With respect to the former problem, I have seen vendors of vesicular film claim that it is superior to silver halide film because it is not as prone to being scratched. Perhaps, technically speaking, it doesn't get scratched as easily, but it is very easily scored and although the film itself may not looked scratched, the projected image certainly does. I have seen examples of silver halide, diazo, and vesicular films which were tested in a special device designed to scratch film, and in this instance the vesicular film was most damaged, followed by the diazo, with the silver halide the least damaged. Since emulsion on silver halide film is vulnerable to scratching this result was somewhat unexpected, but the damage to the vesicular film was exactly what I have observed in our own collection.
As far as overheating goes, again the problem varies depending upon the particular vesicular film you have. Some are more heat resistant than others are, but no purchaser of vesicular film I ever met had any idea of how heat resistant his or her film was. Many film readers reach film gate temperatures beyond the resistance limit of any vesicular films. "The essential fact to keep in mind about vesicular film stability is that even very short exposure times to elevated temperatures will destroy the image." (Adelstein, p.336.)
In libraries, patrons often forget to switch off the readers and wander away, leaving the film to bake. After a few hours, if the film is diazo or vesicular, the images in the area exposed to the light and heat may be gone. I'm sure this kind of thing can, and does, happen with office records.
Microfilm is subject to damage from a variety of sources, including atmospheric pollutants. Such things as sulphur-based gases (which are especially prevalent in urban and industrial atmospheres) can produce detrimental effects. Peroxides (given off by some papers) are harmful to microfilm, as are ozone and ammonia, out-gassing from wood and particleboard, adhesives, paint fumes, and other gaseous impurities. High humidity and high temperatures are harmful and can lead, among other things, to mould. However, among the main threats to the longevity of any film types are improper storage and careless handling. Users of microfilm represent one of the worst environmental hazards: careless handling results in scratches, tears, and surface pollution. To preserve microfilm for as long as possible, good housekeeping and cleanliness are, obviously, of prime importance.
Proper storage is crucial to the longevity of all film types. ANSI/AIIM TR13 gives specific advice for Extended-term storage (LE-100+), and Medium-term storage (LE-10). LE stands for "Life Expectancy" and the numbers represent the minimum number of years a film should last. The temperature and relative humidity required for extended-term storage are, however, not that difficult to achieve: temperatures for extended-term storage must not exceed 21 C (70 F), and the relative humidity range must be 20% to 50%. Conditions are somewhat stricter for colour films, but in any case these are shorter-lived than black and white films.
ANSI/AIIM TR13 explores, in some detail, the topics I have mentioned, and explains how to store your films correctly and how to inspect them for signs of deterioration. It includes a list of sixteen signs of deterioration and the probable causes. One of the worst problems in older collections is the deterioration of the cellulose base in cellulose acetate films. This is known as "vinegar syndrome" because the breakdown of the film base produces acetic acid (vinegar). Any films found in this condition must be removed immediately, because once the process begins it can infect other cellulose acetate base films stored in the same area, so great care must be taken to detect the problem as soon as it begins. Another problem that is common in silver halide films is redox blemishing (reduction-oxidation), sometimes known as "measles," "red spot," or "mirroring." These blemishes are caused by the oxidation of the silver in the film but now, thanks to the Image Permanence Institute at the Rochester Institute of Technology, there is a way to prevent these or to halt their progress. The IPI has produced an invaluable publication entitled IPI Storage Guide for Acetate Film (Reilly, James M.) which, although it is directed to films with cellulose acetate base, provides information relevant to the storage of all film types.
Microfilm is, in my opinion, an eminently suitable medium for the preservation of information. It is durable (depending upon the type of film you choose), long-lived, and relatively inexpensive. But most of all – and I don't think this can be stressed too often - the information on it is retrievable by the human eye. Only printing or chiseling on stone can match this!
Adelstein, Peter Z.
"Preservation of Microfilm." Journal of Micrographics
11, no. 6 (July/August 1978): 333-37.
ANSI/AIIM TR13-1998. Technical Report for Information and Image Management -
Preservation of Microforms in an Active Environment - Guideline. Silver
Spring, MD: Association for Information and Image Management International,
Jones, Mark L. Fading of Diazo Microfilms in Readers. Hatfield, England:
National Reprographic Centre for documentation, 1978. (NRCd Publication
Reilly, James M. IPI Storage Guide for Acetate Film. Rochester, N.Y.:
Image Permanence Institute, Rochester Institute of Technology, 1993.
Reilly, et al, New Approaches to Safety Film Preservation. NEH Grant
PS-20445-91. Rochester, N.Y.: Image Permanence Institute, Rochester
Institute of Technology, 1994.