Exploring

Inherent Vice: Magnetic Media

Tape Recording Layer

Magnetic tapes have a recording layer of magnetic particles (iron oxides in acetate magnetic tape; iron oxides, metallic iron, or chromium dioxide in polyester tape) suspended in a polyurethane binder. The binder may also include lubricants and other agents used to improve tape performance. Some tapes also have a binder coating on the back of the tape to reduce friction as the tape moves through the player and to make the tape wind more uniformly on the reel.

Binder Deterioration

The primary means of deterioration for all types of magnetic tape is binder degradation, also known as sticky shed syndrome. The polyurethane binder is subject to hydrolysis, in which moisture is absorbed by the binder material and longer molecules within the binder are broken up into shorter ones. The result is a softening of the binder and the presence of a gummy surface residue on the tape. The residue makes the tape stick in the recorder and causes uneven playback, sometimes making the tape jam completely. Occasionally, cleaning or baking the tape will make it usable for long enough to copy it, but this must be done by an experienced professional.

An additional problem with the binder is the loss of lubricants over time, which can be due to evaporation, to use of the lubricants during playback, or to hydrolysis or oxidation of the lubricant itself. Lubricant loss will also cause sticking, uneven playback, or jamming of the tape. Relubrication of tapes is possible, but must also be done by an experienced professional.

Magnetic Particle Deterioration

The magnetic particles that store the recorded information are subject to changes in their magnetic properties that can result in loss of the recorded signal. Although the extent of their vulnerability varies, all tapes are subject to demagnetization from exposure to a strong magnetic field, so care must be taken to avoid exposure.

Some magnetic particles are more stable than others (e.g., they keep their magnetic properties longer and are more able to resist demagnetization). Iron oxide particles are the most stable; these are generally used in lower grade audiotapes and low to high grade VHS/Beta videotapes. Metal particulate and chromium dioxide particles provide a higher quality output (hence they are used in high quality audiotape), but they are less stable. Metal particulates are also used in 8mm videotape and digital audio and videotapes. The rate of metal particulate and chromium dioxide deterioration is dependent on temperature.