[78-L] Glass Compound 78s

[David Lennick]

Michael Biel wrote:
> 
> As dl mentioned, professional grade discs were not marked on the discs
> themselves, only on the sleeves which often can get switched so that a
> glass base sleeve could house an aluminum disc, but most home-grade
> glass base discs are marked on the manufacturer's label.  But glass was
> rarely sold to the home recording market.  They used steel base and
> fibre base discs.  Many radio and recording studio labels did mark the
> discs as glass, but not always because the labels were sometimes
> prepared by a secretary, not the recording engineer.  The first glass
> Presto discs were very thick and had a metal grommet in the center hole.
>  AudioDevices' AudioDisc brand had a fibre-center that was about
> 2-inches in diameter, and the edge of how this fits into the larger
> glass hole can sometimes be seen or felt.  Later in the war Presto had a
> printed label that said glass base, but I am not sure if the discs were
> shipped with this label on them or if it was to be applied by the user.
> 
> As to whether glass discs were more flexible when new, I doubt that
> because one of the reasons glass was used was because it was less
> flexible than aluminum.  One of the selling points of glass prior to the
> war was that it was ideal for use for mastering because it remains
> flatter than metal when being electroplated.  The first glass discs were
> shipped in early April 1941, prior to our entry into the war, and before
> aluminum rationing.
> 

I didn't know that glass discs preceded Pearl Harbor in the US, but they were 
definitely in use in Canada prior to that date..the CBC has many such from 
1940. Heavy, but not the super thick ones with the grommet .. man, those things 
must weigh five pounds. Even the twelve-inch ones (of which I have two, from 
1942) are hefty. And prone to cracking.

It should also be noted that studios often didn't attach labels to discs at 
all, but wrote the info in grease pencil or scratched it into the label area.

dl