Erik’s talk provided a survey of deterioration mechanisms and the evolution of corresponding treatment literature, as well as some novel approaches to condition assessment and treatment.
He opened with a discussion of “sticky shed” syndrome, in which a hydrolysis reaction in an environment with high RH causes the binder layer on magnetic tape to become unstable. During playback, this softened binder leaves a residue on the playback heads, which can damage the tape and clog the heads. While waveform monitors and vectorscopes can’t help diagnose this condition, a less common scope, tracking RF (the unmodulated RF signal put into waveform) can give a kind of “EKG” of the video signal. Erik showed normal vs. abnormal RF envelopes — the abnormal one indicates head-clogging due to sticky shed. This causes loss of signal and eventually complete loss of image. RF monitoring can help differentiate between sticky shed and other issues, such as a transfer done with an overstretched tape, poor head alignment, and deterioration due to tape wear. For instance, abrasive wear (such as that caused by a particulate scraped down the tape) can cause a ripple in the RF but looks very different on the scope from the abnormal RF envelope caused by sticky shed.
Erik also described the damage that could be caused by abrasive wear. He described various surface cleaning methods that can be employed to remove particles that could cause abrasive damage during playback. These include cleaning open-reel videotape by wrapping dusting paper around the playback heads; however, some tapes have a carbon black back-coating that is susceptible to sticky shed, so it is important to verify that neither the magnetic binder nor the back coating are compromised before cleaning. Other cleaning methods have included using isopropyl alcohol to clean the tape during playback, and using Pellon on both the oxide layer and carbon black back-coating to trap loose oxide particles, along with a vacuum to draw those particles away. Surface cleaning machines integrating these methods can be purchased off-the-shelf (such as Bow Systems 432 open-reel videotape cleaner for enterprise-level use). Alternatively, Erik showed a prototype for a cleaning machine that he is presently testing with Video Data Bank (VDB). It uses open-source circuitry (Arduino-based), approximately $1,200 in parts, and custom spindles. The design is available on GitHub: epiil open-cleaner.
Erik discussed the history of thinking on the baking of tapes exhibiting sticky shed. While this may temporarily restore binder integrity to enable transfer of the content, it does not cure the condition, and is controversial. Some maintain that baking damages the behavior of oxide particles, as well as the mechanical behavior of the pack, while others see it as necessary in order to rescue content from deteriorating sources.
In terms of condition assessment, several research projects are underway to advance scientific understanding of deterioration mechanisms. Among these is the University of South Carolina’s development of a non-invasive test for sticky shed using ATR-FTIR. Not only does this kind of scientific research enable the field to develop best practices based on data rather than anecdotal evidence, it also gives practitioners much-needed tools for non-invasive condition assessment. Presently, condition assessment is largely accomplished through observation of playback, which can cause damage before vulnerability can be ascertained.
Throughout the presentation, Erik shared resources to consult that show the evolution of approaches to condition assessment and treatment of magnetic tapes:
- Bharat Bhutan, “Mechanics and Reliability of Flexible Magnetic Media” Springer; 2nd edition (May 31, 2000)
- Walter Forsberg & Erik Piil, “Tune In, Turn On, Drop Out: Section 108(c) and Evaluating Deterioration in Commercially Produced VHS Collections” Annual Review of Cultural Heritage Informatics 2012-2013, Facet Publishing (July 2014)
- Tony Conrad, “Open Reel Videotape Restoration” The Independent, AIVF, Volume 10, Issue 8, Number 8 (1987) – describes what was a pioneering treatment at the time for sticky shed
- Charles Richardson, “The New “Non-Baking” Cure for Sticky Shed Tapes” ARSC Journal, Vol. 44, No. 2 (Fall 2013) – makes a case against baking; advocates for adoption of the cleaning machine developed by the author
Erik invited the audience to visit GitHub to follow the progress of his affordable, open-source open-reel videotape cleaner, and to contribute or comment. This is an exciting project that will make a quality cleaning machine feasible for institutions on limited budgets. The novel use of the tracking RF scope and the look at historic as well as contemporary treatment literature for videotape conservation were two other highlights of this talk.