Preservation of magnetic audiotape

Multiple types of magnetic media exist but are mainly in the form of open reels or enclosed cassettes.

They were designed with iron carbonyl as the magnetic pigment mixed into the cellulose acetate carrier.

Production soon moved to iron oxide coated onto cellulose acetate rolls cut into uniform strips wound onto plastic or metal hubs.

Tape consists of a coating of a magnetic pigment, typically iron oxide (Fe2O3), on a long strip of polyester (polyethelyne terephthalate) base film.

A new problem with chemical stability became notable in the mid-seventies when two significant tape manufacturers changed their dispersion formulations by introducing a polyurethane binder that, in time, turned hygroscopic and broke down as it absorbed water molecules into the long hydrocarbon molecular chains.

Information can be recovered from the "sticky-shed" tapes by heating them at a very low temperature in order drive the water out of the binders.

The website for sound preservation hosted by the National Library of Canada classifies dirt in two classes: Foreign matter (fingerprints, dust) and alteration of the original state (chemical reactions caused due to grime and dirt deposited on the tape surface).

They are generally correct to recommend this, as it is a delicate process that requires training if one plans to undertake serious chemical or physical repair.

The Library of Congress [3] recommends that any tapes needing preservation for a minimum of 10 years should be stored between 65–70 °F (18–21 °C) at 45-50% relative humidity (RH).

In the case of magnetic tapes, contrary to traditional preservation storage rules for books and photographic film, colder is certainly not better.