From: Steve Greene <[log in to unmask]>
> I wasn't aware that steel was widely used.
It was the ONLY metal used for home discs during the war. It wasn't
used much for professional discs because of the weight of professional
> I ran into a few War era disks that originally thought were lacquer.
They're all lacquer except for some celluloid coated discs, mostly
> A few of them had one crushed edge from rough handling in a steel cabinet
> and we determined they had a fiberboard base.
Fibreboard was widely used for the most inexpensive grade of home discs
from long before the war thru long after the war. They were both
lacquer coated or covered with a clear celluloid sheet. Almost all of
the soldier voice records mailed to family were made this way. Fibre was
rarely used for professional discs because they are too flexible in
large sizes, as well as having a LOUSY surface!
> Glass was more commonly used, especially from '42-'46.
The first Presto and AudioDisc glass discs were shipped in April 1941 so
they can show up before Pearl Harbor day. They restarted using aluminum
in the fall of 1944, although stocks of glass lasted as late as 1948.
There were companies which had a service of stripping your old aluminum
discs and re-coating them, so that is an explanation of some aluminum
discs showing up during the war.
> Glass was usually carefully marked as such because of the breakability.
> If not marked, glass is heavier and has almost no "flex" to it.
Presto said it was experimenting with glass at first because of the lack
of flex which was an important problem with using lacquer for disc
mastering instead of wax. That is why CD masters are glass. The first
Presto glass discs were twice as thick as ordinary discs, and they were
very heavy. But I have always felt that a regular glass disc was
slightly lighter in weight than aluminum. When I was heavily into
working with ETs I usually could tell glass when first picking one up.
> Another giveaway is that if a glass disc is gently tapped on the edge, it gives slight ringing sound.
Aluminum discs also ring. But sometimes you can hear that there is a
crack in the glass when the ring is a thud. Most glass discs are
translucent, but some are almost opaque. Hold them up to the light --
although it is safer to have a light below the discs so you don't risk
holding them up high!
The edge and the center holes of glass discs are usually an indication
because except for AudioDiscs the holes are drilled before coating. If
the discs are made by spraying or dropping the coating while the discs
are on a conveyor belt, the holes will be coated. If the discs were
made by dipping -- as almost all home discs were -- there is no lacquer
in the center inch or so, so the substrate shows thru.
> Aluminum discs usually show a metallic cross section where the hub was
> punched for the spindle. I've heard rumors that some glass discs were
> bonded to an aluminum hub, though. Hope this helps. Steve Greene
Almost all glass AudioDiscs had a fibre center hub about 2 1/2 inches in
diameter which can have holes that look metallic because the metal on
the turntable spindles can rub grey coloring onto the holes if the discs
were slip-cued. If there are no paper labels, those center cores are
easy to spot, but if there are well-applied paper labels you might not
notice the outer diameter of the fibre core. AudioDevices cut the large
hole in the glass and placed the fibre center in before coating, so the
lacquer coating is what holds the core in place, although it sometimes
falls out. I've never seen a glass disc with an aluminum center hub.
Mike Biel [log in to unmask]
>>> John Dawson <[log in to unmask]> 4/23/2012 3:36 PM >>>
I was wondering if anyone had tips/resources about determining whether
or not a the substrate of a laquer is steel or aluminum. I have some
WWII era discs and some are definitely heavier and sturdier than others.
I am wondering if these are steel.
Media Preservation Initiative