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From: John Dawson <[log in to unmask]>
> So while we are on the topic, how about Zinc discs?

Good question.  I am not sure if it was every used as a substrate in the
lacquer era. It might not have had good adhesion and was very heavy. 
But a non-magnetic heavy disc might turn out to be zinc. 

Zinc had two places in phonographic history.  Berliner used it in the
1890s as material that was acid-etched after a groove in a wax coating
was cut to reveal the zinc that a bath in acid would create the groove. 
This was necessary to avoid the patents that controlled cutting a
groove.  The acid created the groove that was actually used for
mastering or playback.  In the 1920s there was a pre-grooved zinc disc
that you could put on your acoustical phonograph and when you shouted in
the horn it would create dimples in the pre-groove which could faintly
produce sound when played back.  One of these discs had the apt name of
Echo.

Mike Biel  [log in to unmask]