Gramophone or Phonograph Records
Most gramophone or phonograph record disks in library and archive collections are made of polyvinyl-chloride or shellac. Gramophone records have some raw materials in common with books and manuscripts: they use lampblack, and ground wood is often used as a filler for shellac disks. Disks generally are in three sizes: 12 inch (usually long-play records at 33 1/3 revolutions per minute, or rpm), 78 rpm records, and 7-inch (usually 45 rpm).
Record disks are usually housed in paper sleeves and labeled on paper. Thus the commercial packaging is a vital part of the disk provenance. Appropriate packaging and housing for disks are important, because the sound quality is affected by dust and mold gathering in the grooves. A dust-free environment is desirable for the storage and use of disks. If the storage area cannot be maintained, a tightly closed steel cabinet can reduce dust contamination.
Another major concern is the warping that can result from the slumping of disks stored vertically. This can also adversely affect the sound quality. Disks can be stored vertically but in a fashion that prevents them from slumping and keeps them perfectly upright (see Conservation for remedial treatment and correct housing).
Magnetic Audiotape
Early magnetic audiotape from the 1950s and 1960s utilized an acetate film base, which can deteriorate relatively quickly. Modern tape uses a polyethylene terephthalate (PET) film base with an iron-oxide coating bound with polyurethane. Chromium-dioxide has been used on some tapes with a PET coating.
Most older forms of audiotape should be considered chemically unstable if kept at temperatures above 20 degrees Celsius and relative humidity above 40 percent. An acetate film base should be considered less stable than polyethylene and "dubbed" (copied) onto a polyester film base. Thin tapes, typically used in audiocassettes, are inappropriate for archival retention; the thinner tape allows stretching and "print-through," in which sounds from both sides can sometimes be heard. (See Conservation for information on conservation and care.) As with most forms of sound recordings, maintenance of playback equipment is of prime importance.
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