Editing Golden Age of Radio (section)

===Electrical transcription discs===
{{main|Electrical transcription}}
[[File:War of the Worlds ET.jpg|thumb|150px|right|''[[The War of the Worlds (1938 radio drama)|The War of the Worlds]]'' radio broadcast by Orson Welles on electrical transcription disc]]
Before the early 1950s, when radio networks and local stations wanted to preserve a live broadcast, they did so by means of special [[gramophone record|phonograph records]] known as "[[transcription disc|electrical transcriptions]]" (ETs), made by cutting a sound-modulated groove into a blank disc. At first, in the early 1930s, the blanks varied in both size and composition, but most often they were simply bare aluminum and the groove was indented rather than cut. Typically, these very early recordings were not made by the network or radio station, but by a private recording service contracted by the broadcast sponsor or one of the performers. The bare aluminum discs were typically 10 or 12&nbsp;inches in diameter and recorded at the then-standard speed of 78 [[Revolutions per minute|rpm]], which meant that several disc sides were required to accommodate even a 15-minute program. By about 1936, 16-inch aluminum-based discs coated with cellulose nitrate lacquer, commonly known as [[Acetate disc|acetates]] and recorded at a speed of 33{{fraction|1|3}} rpm, had been adopted by the networks and individual radio stations as the standard medium for recording broadcasts. The making of such recordings, at least for some purposes, then became routine. Some discs were recorded using a "hill and dale" vertically modulated groove, rather than the "lateral" side-to-side modulation found on the records being made for home use at that time. The large slow-speed discs could easily contain fifteen minutes on each side, allowing an hour-long program to be recorded on only two discs. The lacquer was softer than shellac or vinyl and wore more rapidly, allowing only a few playbacks with the heavy pickups and steel needles then in use before deterioration became audible.

During World War II, aluminum became a necessary material for the war effort and was in short supply. This caused an alternative to be sought for the base on which to coat the lacquer. Glass, despite its obvious disadvantage of fragility, had occasionally been used in earlier years because it could provide a perfectly smooth and even supporting surface for mastering and other critical applications. Glass base recording blanks came into general use for the duration of the war.<ref>{{cite web | url=http://www.otrsite.com/articles/artwb006.html | title=Music Electrically Transcribed! | author=Beaupre, Walter J. | access-date=2007-11-05 | work=The Vintage Radio Place | archive-url=https://web.archive.org/web/20071109122453/http://www.otrsite.com/articles/artwb006.html | archive-date=2007-11-09 | url-status=live }}</ref>