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So while we are on the topic, how about Zinc discs?

-----Original Message-----
>From: Michael Biel <[log in to unmask]>
>Sent: Apr 23, 2012 6:28 PM
>To: [log in to unmask]
>Subject: Re: [ARSCLIST] Determining substrate of laquer discs
>
>From: Steve Greene <[log in to unmask]>
>
>> John,
>> 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
>thickness grades.
>
>> I ran into a few War era disks that originally thought were lacquer.
>
>They're all lacquer except for some celluloid coated discs, mostly
>fibreboard.
>
>> 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 >>>
>Hi everyone,
>
>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. 
>
>John Dawson
>Indiana University
>Media Preservation Initiative
>