Re: [ARSCLIST] identifying acetate substrates

[Eric Jacobs <ericj@xxxxxxxxxxxxxxxxxxx>]

All the discs are opaque even with strong backlighting.  Does that mean that
they are not glass?  The discs themselves don't say "glass", but archivist's
notes say "glass".


-----Original Message-----
From: David Lennick [mailto:dlennick@xxxxxxxxxxxx]
Sent: Thursday, July 21, 2005 2:11 PM
To: ericj@xxxxxxxxxxxxxxxxxxx
Cc: ARSCLIST@xxxxxxxxxxxx
Subject: Re: [ARSCLIST] identifying acetate substrates


If they say glass, chances are they ARE glass, especially if the center
portion
looks removable. Very carefully hold one up to the light..if it's glass,
you'll
see through it. During a specific period, about 1941 to some time in 1945,
aluminum discs were very difficult to obtain since aluminum was needed for
war
materials. Glass and paper went in as substitutes. In Canada, the CBC began
recording on glass discs in 1940 (which raises the question as to why this
happened, if Canada didn't have a company manufacturing recording
blanks....)

Not all glass discs have the cardboard centre (which is under the label and
theoretically shouldn't be removable, but then was then and now is now). I
think
Presto discs are glass right to the center hole.

dl

Eric Jacobs wrote:

> I'm working on a set of 16-inch acetates from the 1940s, and some are
> manufactured on what appears to be a particulate substrate (looks like
wood
> chips when you look at the spindle and registration holes).  Looking at
the
> edges, although no edge is fully exposed, it appears that the particulate
> substrate is used throughout the disc.  These are war-era discs, which is
> why they are not the usual aluminum substrate.  The discs are "audiodisc"
> brand (models 2063, 9083, 9112, 9115, 9122).
>
> Here are my questions:
>
> 1.  I would like to know more about this particulate substrate - its
> composition and so on, and if it might require different storage than
> aluminum or glass substrate discs.  The discs were identified as "glass"
> substrate, but the particulate substrate doesn't seem consistent with or
> look like a glass substrate.
>
> 2.  These particulate substrate discs have what appears to be a "knock
out"
> center (66 mm diamater).  Would anyone know if there was such a thing as a
> turntable with a 66 mm spindle?  I'm curious as to why these would have
what
> appears to be a removable center.  Was this simply a manufacturing
process,
> or might it have been functional?
>
> 3.  How do you identify a glass substrate acetate disc?  Was the glass
> substrate continuous, or was the center spindle/label area one type of
> material (aluminum?) which was then bonded to a glass substrate annulus?
>
> 4.  Has anyone cataloged the various 16-inch acetates by brand, model
> number, and composition?  I'm finding some patterns of palmitic acid
> formation which might correlate to the type of acetate disc.  My sample
size
> is not large enough yet to draw any conclusions (and I need to research
> storage conditions more), but this could lead to some knowledge about
which
> types of acetate discs may or may not be more prone to deterioration.
>
> Eric Jacobs
> The Audio Archive