Anticipating Preservation Needs of Archived Audio Tapes

The following is a post by Andrew Davis, a chemist in the Preservation Research and Testing Division. Andrew works to understand polymeric materials in the Library’s collection, such as paper, adhesives, and audiovisual materials and also researches the effects of light and the environment on collections objects.

For archivists, audio professionals, and audio hobbyists, the decay of some open reel audio tapes is well-known. Open reel tapes are typically made from plastic film, coated with a layer of magnetic particles dispersed in a binder. This material is notorious for developing a range of physical maladies, such as “sticky-shed” syndrome, where deterioration of binders on the tape occurs and causes sound or information loss due to squealing, slowdown, or shedding when played back.  Fortunately, there exist some generally accepted remedies that can help access many of these tapes’ recordings for long enough to transfer their contents, but what should we do with older tapes that still seem in good playable condition? Are they about to imminently turn sticky? How worried should we be about those seemingly good ones? These are interesting questions for us because the Library of Congress has a LOT of recordings on audio tapes.

We recently published some results addressing that question for polyester-based magnetic tape, as an outcome of a scientific study undertaken in collaboration between scientists at the Library with colleagues at FUJIFILM. This report is available from the Council on Library and Information Resources.

A big takeaway from our work is this: we probably don’t need to worry too much about those “good” polyester-based magnetic tapes rapidly turning unplayable. As hard as we pushed them in our testing, they appear to be quite stable; these good quality tapes will likely remain stable for decades.

This work primarily relied on taking matching test tapes which were in good condition (all non-Library-collection tapes coming from CHARM – our scientific reference and testing collection) and exposing them to various mixtures of high or low temperature and humidity at levels known to accelerate physical and chemical degradation reactions.

After a full year of artificial aging, we measured a range of scientific material properties (friction when sliding over a surface, molecular weight of their constituent polymers, etc.) and compared those to the same properties from degraded tapes which we knew exhibited playability problems.

On the whole, we found that after year-long exposure to these conditions the tapes’ coefficient of friction didn’t change, the roughness of the tapes’ surfaces didn’t change, magnetic properties like saturation and susceptibility were unchanged, and the concentration and size of the tape’s polymeric molecules only changed at harshest temperature condition (and even then, only slightly). Overall, not a lot happened.

To be honest, the fact that not a lot happened was disappointing at first. We initially hoped the experimental aging and testing would induce common degradation symptoms into those seemingly good tapes. If we could make them sticky (or squealing, or shedding, etc.) in a controlled way, then we could better study the way to prevent or treat those symptoms. But we couldn’t do it. These tapes, all from a potentially concerning vintage, started in a good and playable condition and stayed that way. After applying a few standard methods to use time, temperature, and chemical data to extrapolate how our measured values would behave over more reasonable storage or office environments, our measured data suggested that these tapes would likely retain their stability for many decades – possibly up to 100 years.

This lack of dramatic degradation became more interesting the more we thought about it. As we noted in the report, a number of older and still-used preservation guidelines predicted 10- to 30-year lifetimes for existing polyester-based audio tapes. (Van Bogart, John W. C. 1995. Magnetic Tape Storage and Handling: A Guide for Libraries and Archives. Washington, DC, and St. Paul, Min­nesota: Commission on Preservation and Access and National Media Laboratory). The tapes we tested came from the 2000s to 2010, putting them firmly within this age of concern. Some additional anecdotes have noted occasional preservation worry about these specific models of tape. Yet, not only were they easily playable from the start of the study, they remained so after pushing them at conditions which accelerate degradation. From that view, the results from this work seemed a lot more interesting. At the very least, it suggests those guidelines and suggestions may be overdo for revision.

This work does require noting a few important caveats:
First, environmental storage is still important. It’s one of the few factors within the control of tape users. Even though only the most extreme of our test environments caused any measurable change, those changes were consistent with hot and humid hydrolysis of the tapes. So, while we cannot always untangle old problematic manufacturing formulations, we can at least try to limit polyester-based tape exposure to excess heat and humidity.

Second, this work is clearly most applicable to the specific models of tape tested in our labs. Recordings in the real world will always have their own unique history, and exact quantitative predictions of longevity might not fit them perfectly. That said, polyester-based tapes share much chemistry, so we are hopeful that these trends of good tapes remaining playable could apply to other polyester-based tapes.

Finally, tape equipment is not nearly as ubiquitous now as it was years ago. Ongoing access to physical playback equipment and enduring user expertise is at least as much of a preservation concern as the physical integrity of the recordings themselves. It’s important to know and understand both issues so that users are not stuck with working equipment but unplayable tapes, or perfectly preserved audio tapes without a working deck to play them on. As Michael Heller succinctly wrote about the archival anxieties of tape: “After all, what good is a tape we cannot hear?” (Heller 2017)

Acknowledgement: The planning and preparation of this collaborative research project spanned a number of years and additional Library staff, both past and present, and their efforts have been much appreciated.

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References

Michael C. Heller (2017) Orpheus unglued: sticky shed syndrome and tape’s archival anxieties, Sound Studies, 3:1, 64-70, DOI: 10.1080/20551940.2017.1341460