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Friday, May 12, 2017

Q. Can you identify my discs?

Following a recent lesson I had taught on music technology history, one of our teaching assistants mentioned that she had found some five-inch discs at home in her loft.
Q. Can you identify my discs?They appear to be thin steel discs coated in what seems to be thick varnish. The groove is clear to see but the material has cracked in places. I tried to get my Technics deck to play them but they are too small and the arm returns too soon. I have a gramophone, but I think that the arm and needle could scratch the surface off.
David Cooke's mystery aluminium discs.
Do you think that they could be some sort of home recording? Perhaps pre-tape, or at least pre-consumer tape machines? Possibly even 'end-of-the-pier' booth recordings?

David Cooke
Technical Editor Hugh Robjohns replies:
I think you are right, David. These look as though they are the kind of discs that might come from an end-of-the-pier or music shop automatic booth recorder, dating back to the 1940s, at a guess.

David Cooke's mystery aluminum discs.

It's all well before my time, of course! So, I made a few enquiries of my elders and betters (many thanks, Pete), and was told that five-inch discs such as these were made in automatic booth recorders. The discs play at 78 rpm and the recording was usually cut directly into bare aluminium. However, some discs were made with coated aluminium, as these pictures appear to show. The coating was either acetate or a type of gelatine that was water-soluble (and easily damaged, as you can imagine). It's hard to tell from the photo which type these are, but the obvious shrinkage and peeling means that they need to be transferred fast if the material is of some value, as this deterioration will almost certainly accelerate.

Something else to bear in mind is that a lot of these records were made using the old 'hill and dale' groove technique. This technique used vertical groove modulation, rather than the side-side modulation format that became the norm for commercial discs (or the 45/45 format used in modern stereo microgroove records).
Again, it's hard to tell from the photo, but the grooves on the pictures make me think that these are hill and dale recordings (unless the light is playing tricks).

Published May 2008

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