Exploring

Inherent Vice: Magnetic Media

Tape Substrates

The first magnetic tapes used a backing (carrier) made of steel. During the 1930s, German companies developed an audiotape that used a plastic carrier coated with a powder made from material that could be magnetized. At that point, the recording quality of magnetic tape had improved enough to compete with the best disc recorders, and after the end of World War II it gradually became more widely used.

Acetate tape is easily distinguishable from polyester tape: light shines through an acetate tape pack.
Courtesy of Stanford University Libraries

The backing for magnetic tape provides support for the magnetic recording layer as it travels through the tape recorder. Magnetic tape for sound recordings was produced on both acetate and polyester backings, while videotape was produced only on polyester. In magnetic audiotapes, the plastic backing is much thinner than in film, making it much more fragile.

Characteristic Types of Deterioration

Acetate magnetic tapes, like acetate films, suffer from vinegar syndrome, which is described in detail in the section on acetate film. The tapes will emit a vinegar smell and eventually the backing will become brittle and shrink. Polyester tape is much more stable chemically (it is very resistant to oxidation and hydrolysis), but it is subject to physical distortion and mistracking of the tape due to poor winding of the tape pack and/or changes in temperature and relative humidity. See Magnetic Tape Storage and Handling for illustrations of poorly wound tape (you will need to scroll down the page).