AIC's 47th Annual Meeting

Audio engineers, audio tape users, and researchers using audiovisual collections have spent decades studying the degradation of polyurethane-based magnetic tapes. When played, degraded tapes can introduce noise into the original recordings, shed material from their surface, or lose their magnetic data coatings entirely. These problems can permanently ruin a tape and jeopardize its contents, and residues from degrading tapes can cause harmful effects to expensive playback machines, which are frequently in short supply for many smaller archival institutions. Frustratingly, problems arising from any specific tape may not be evident until that tape is on the playback deck, partially played, and too late for remedying. Even if degradation is suspected, some tape users express worry about possible consequences from common “baking” treatments and may hesitate to apply treatments unless absolutely necessary. A cheap, rapid, and non-technical tool to evaluate the condition of a tape prior to playback might tremendously aid users in their daily workflow and aid in the preservation of magnetic media. This project was inspired by specific concerns from the audio community and started as a desire to find new methods to rapidly evaluate our own collection. However, it more broadly demonstrates how seemingly simple tools can empower a wide range of users with novel methods they likely have available already.

The work presented here will describe how a droplet of water can be used as a simple tool to assess tape condition prior to playback and prior to treatment, for which no predictive tool currently exists. This method requires no expensive equipment and minimal scientific training. Water contact angle is a tool used widely in the surface science fields to characterize the surface of a material. This method involves application of a micro-liter sized water droplet to the surface of interest, followed by evaluation of the droplet shape, either by qualitative visual inspection or by quantitative calculations. The shape of this droplet varies according to materials’ surface tension and is intimately related to the chemistry and texture on that surface. Sample audio tapes from the Center for the Library’s Analytical Scientific Samples were used to assess the viability of using contact angle as a predictor of tape condition. Tapes were chosen with known states of degradation based on previous playback attempts, and samples included tapes from a range of different manufacturers with different tape composition. Tape condition and playability was found to strongly correlate with the water contact angle of the tape's magnetic layer, with lower contact angles generally revealing degradation problems. In a promising development, contact angle results were able to accurately predict the playback condition of a previously unplayed and uncategorized tape, as well as identify multiple labeling errors where the playability of a tape did not match its noted condition.

Additional experiments are ongoing with researchers beyond the Library of Congress, providing valuable “real world” insight into possible variations from individual users across a wider selection of institutions.