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Aluminum disc recordings, used in the nineteen-thirties and forties, were made by a stylus scratching directly onto the aluminum. These recordings are highly durable, though they might be damaged by repeated playing or improper storage.
But the durable aluminum discs could not be re-recorded and most recordists preferred using an acetate (plastic) coating on the aluminum disc, which then could be re-melted and re-recorded. Over time, however, the acetate coating "extruded" or gave off softeners, which appear as a white dusty coating on the surface of the disc. This diminishes the sound quality. Eventually, the acetate will dry out and flake off the aluminum base, destroying the recording. Glass was used as a base for acetate disc recordings during World War II, when aluminum was required for the war effort. These glass discs are very fragile, and are easily broken.
All disc recordings may be damaged simply by playing them. To play an early disc so that the sound may be copied onto a preservation medium, special needles must be used. A modern phonograph needle would destroy the recording.
In the late forties, recordists began using magnetic media to record sound. Both tape and wire recordings were developed. Wire had the advantage of producing high quality sound, but the hair-thin wire easily tangled. The recordists carefully taped down the ends of the wire to prevent them from uncoiling and tangling, but over time these small pieces of adhesive tape dry out and the wire tangles. As a sound engineer attempts to rescue the tangled wire, it often breaks. Though it can be respliced, it must be played to be sure that the fragments are assembled in the right sequence, and that no segments are put together backwards. Because wire recording was used for only a short period, wire playing equipment is especially difficult to find.
Tape recording uses iron oxide on paper tape or plastic tape to make the magnetic recording. Paper tape, like all acidic paper, becomes fragile over the years.
Paper recording tape was used for only a short time, though it did produce good quality sound recordings. The first plastic tapes were acetate, and suffer similar problems as acetate disc recordings. Also, the coating on early plastic tapes can flake off or deteriorate, making it difficult or impossible to retrieve sound from the recordings.
Polyester tape, introduced in the sixties, is a stronger backing for the iron coating. If the tapes have been stored in a humid place, they may need cleaning before they can be played. But the polyester base is more durable than acetate, so these recordings may last much longer. High-quality polyester tape is preferred even today as a preservation medium for archival sound recordings. However, even in the polyester tape era, things could go wrong. A problem called "sticky-shed" developed on some recordings made in the late seventies and early eighties because of a manufacturing problem. Tapes with sticky-shed can become stuck together, and must be baked at a low temperature in special ovens to make them playable.
Today, with DAT recordings that may be lost due to unpredictable sound drop-outs, and writable CD recordings that may delaminate and become unplayable, the durability of sound recordings is still an issue. As digital sound technology develops, we may discover better methods to make sound recordings and preserve them.
But preservation of older recordings is a critical task for all sound recording archives. The sound must be retrieved from older recordings before the media they were recorded on deteriorates and the sound is lost forever.
If you would like to learn about preserving your own treasures, the Library of Congress Preservation Directorate provides information on preserving recordings, manuscripts, and photographs:
Save Our Sounds is an official project of the Save America's Treasures program of the National Trust for Historic Preservation.
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