An acetate disc (also known as a test acetate or, in the United States, a lacquer) is an audio disc that is created as part of the process of producing a vinyl record. Acetates are produced from the master tape recording and represent an intermediate stage prior to the production of the master disc - the disc from which retail copies of the recording will be pressed. The purpose of the acetate is to allow the artist, producer, engineer and other interested parties to check the quality of the tape-to-disc recording process and make any necessary changes to ensure that the audio fidelity of the master disc will be as close as possible to that of the original master tape.
Despite their name, most acetate discs do not contain any acetate. Instead, they comprise an aluminium disc with a coating of nitrocellulose lacquer. (Glass was also used during World War II, when aluminium was in short supply.) This production process results in a disc that is different in many ways from the vinyl records sold to customers at retail. Whereas vinyl records are light and semi-flexible, acetates are rigid and somewhat heavier. More significantly, the thin coating of lacquer on an acetate is much more susceptible to wear; the playback head of a stylus quickly damages the grooves of the record such that after only a relatively few number of plays the audio quality is noticeably degraded. This is not a problem, however, since acetates are only test pressings and are not designed to be able to stand the test of time.
Acetates typically come in several sizes: 7" and 10" discs for singles and 12" discs for albums. The record's sleeve is typically nothing more than a generic cover from the manufacturing company and the disc's label is similarly plain, containing only basic information about the content (title, artist, playing time, etc.), which is usually typed but is often just handwritten. Many acetates also have a second hole near the centre hole in order to indicate clearly that the disc is test acetate.
Test acetates have not always been used solely as a means of checking the quality of a disc recording. From the 1930s to the early 1950s, before the introduction of magnetic tape, recordings were often made directly to acetate discs, which then served as the master from which other discs were made. Acetates were also used as a storage medium for radio commercials; since commercials only run for a limited time it doesn't matter if the disc wears out relatively quickly. Also, in the dance music world, DJs sometimes create acetates containing various sounds, samples and loops that they can use during their performance. These discs are known as dub plates.
Due to their rarity, some acetates can command high prices at auction, particularly when the recording never made it to the release stage.
