[ARSCLIST] identifying acetate substrates

[Eric Jacobs <ericj@xxxxxxxxxxxxxxxxxxx>]

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