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]