CHAPTER 4: Magnetic Tape
DECAY
In the early days, carriers of magnetic tape were made of nitrate or acetate film; today, they are made of polyester film. Recent research developments on these materials are described in the chapter entitled "Film and Photographic Materials."
Aging phenomena
Audiovisual data carriers play an increasingly important role in cultural heritage documentation, but they are prone to degradation. From 1993 to 2000, the European Union subsidized the Eurocare AVIDA project (EU 892). Its aims are to clarify the degradation mechanisms of magnetic tape (audio and video) and to identify appropriate conservation measures. The project will create a catalog of conservation and rejuvenation measures. It will be in the public domain and independent of the polymer industry and its trade secrets.
The following institutions are participating in the project:
Austria: Phonogrammarchiv der Österreichische Akademie
der Wissenschaften (life-expectancy studies), Österreichisches
Kunststoffinstitut Arsenal (life-expectancy studies);
Germany: Bundesarchiv (investigation into research needs,
evaluation of ongoing research programs).
Constituent materials and standards
To understand the process of magnetic tape deterioration, it is essential to know something about the constituent materials. Given that most of the crucial information is an industrial secret, this is not an easy task.
Ian Gilmour and a team of engineers from the Engineering and Research Group of ScreenSound Australia (Canberra) are testing magnetic media, particularly in relation to the development of standards. Their goal is to answer such questions as how to measure tape characteristics and performance, how magnetic tapes fail, how to study the aging process, and how to define end of life (EOL) and life expectancy (LE) of tape.
The present research concentrates on magnetic tape constituents, such as metal particles, on different coatings. Among other methods, the research team uses the abrasion testing facility, which was developed by the ScreenSound engineers. The research team also attempted to formulate a workable definition of LE using pigment binder degradation as an indicator (Gilmour, in press).
Life expectancy
LE testing of audio- and videotape is an important and difficult challenge. Experience has often contradicted manufacturers' claims. Standardization of LE testing is advancing slowly, and no serious insight or understanding, based on research by independent laboratories, is available to the public. The chief problem is the lack of knowledge about which tapes will be the first to deteriorate beyond the point where they can be retrieved, which will deteriorate in the midterm, and which will last for another 20 years or more. Such knowledge is a prerequisite for setting up a successful preservation and transfer strategy. For several materials, the LE can be estimated by tests based on the model of Arrhenius; however, this is not possible for magnetic tape because of the temperatures involved in such testing. Alternative minimally invasive or nondestructive methods have to be developed.
As part of the Eurocare AVIDA project, Dietrich Schüller from the Phonogrammarchiv der Österreichische Akademie der Wissenschaften (Vienna, Austria) and Otto Hinterhofer from the Österreichisches Kunststoffinstitut Arsenal (Vienna, Austria) studied various approaches to estimating the LE of magnetic tape. They included mechanical tests to determine the surface hardness of tape against penetration or the resistance of the tape surface against abrasion, as well as chemical methods, such as thermoanalytic tests (e.g., gas thermogravimetric analysis [TGA] and differential scanning calorimetry [DSC]). All these methods are either nondestructive or need only small amounts of sample material. Their reliability and validity, as well as their applicability to the great variety of magnetic tape, have yet to be investigated. A new proposal has been put forward to the European Program of the Institute for Safety Technology (IST) for further research on the life expectancy of magnetic audiovisual data carriers and on other preservation issues of magnetic tape, especially on behalf of the holdings in Eastern Europe (Hinterhofer et al, in press).
TREATMENT
Disaster recovery
Research on modern records has only just begun; for example, there is still little understanding of how media such as magnetic tape would be affected in a disaster.
Joe Iraci from the Canadian Conservation Institute is performing research on the disaster recovery of modern machine-readable information carriers. The project, which includes the examination of magnetic tapes, is divided into four stages: (1) preliminary testing; (2) soaking experiments; (3) investigation of drying techniques; and (4) investigation of cleaning techniques.
STORAGE
The basis for magnetic tape is nitrate, acetate, or polyester film, the same base material used for photographic film. Recent developments in the storage of these materials are covered in chapter 3.