Effects of Desiccation on Degraded Binder Extraction in Magnetic Audio Tape
Norris, Sarah, ARSC Journal
As some types of magnetic audio tape age, they develop a set of problems known as sticky shed syndrome. During playback, affected tapes can produce a squealing sound and leave behind a gummy residue at contact points on the tape machine. This residue accrues and slows the linear speed of the tape, making playback difficult and sometimes impossible. Segments of the magnetic media can detach from the tape, removing recorded information and often reducing sound quality. Sticky shed syndrome generally affects tape manufactured from the mid-1970s to the mid-1980s, and it is a serious concern for the custodians of historical audio collections. Reels of tape cannot simply sit idle on a shelf; they must function in playback at least once for their content to he meaningfully retrieved.
One solution developed by audio technicians to treat sticky shed syndrome is baking. In this treatment, affected tape is exposed to temperatures of 125-135" Fahrenheit for between one and eight hours. This procedure is supported by one patent (Medeiros et al., 1993) and much anecdotal evidence (Norris, 2007), but its effects are temporary, usually lessening the symptoms of sticky shed syndrome for just several weeks. This time provides an opportunity in which to capture one analog playback as a digital recording, which can then function as source material for future use. Baking has been a powerful tool for audio specialists, but it is not effective for all tapes, and there is growing concern that required baking times are increasing as tapes continue to age (Hess, 2008). The future effectiveness and reliability of the treatment is unknown.
While the baking treatment has allowed many sticky shed tapes to be digitally transferred, little discussion has been devoted to the possible negative consequences of placing historical audio artifacts in an oven. The short- and long-term effects of elevated temperature on magnetic audio tape's components, including the magnetic coating. substrate, and back coating, have not been thoroughly studied. Baking is an inherently aggressive treatment that shares much in common with accelerated aging studies, and accordingly risks exposing tapes to activation energies required to initiate degradation mechanisms. Although it is the only commonly accepted technique for remedying sticky shed, the baking treatment may achieve today's playback at an unknown future cost.
The strong need for testing and study of sticky shed syndrome, the baking treatment, and magnetic tape in general is complicated by the formidable uncertainties of provenance that riddle the audio field. Specific chemical formulations of tape components were often considered proprietary and not disclosed by the manufacturers. As a result, current audio specialists lack key knowledge about the composition of their materials. Tape makers and their suppliers frequently made slight changes in their formulations while maintaining the same product identification. Sometimes formulation changes occurred within a single production run, and sometimes product naming and numbering schemes were inconsistent (Eilers, 2000). Today, understanding the fundamentals of these materials is becoming an increasingly daunting task as tape manufacturers cease production and technical support for the format dwindles.
Further, it is often impossible to make a visual identification of the manufacturer or type of tape. The tape itself usually bears no distinguishing mark. Reels and boxes may carry those marks, hut after years of practical use, these accompanying materials are seldom original. As a result, audio specialists often work with tape of completely unknown origins.
These difficulties of provenance create a serious handicap for controlled research in the audio field. Accordingly, audio professionals have been forced to develop working solutions, like baking, without significant scientific foundations. Further research into these topics could help to standardize practices and establish treatment solutions that are more strongly rooted in conservation ethics. …