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George - a wonderful and valuable response, thanks so much for this.

Has this type of knowledge been documented somewhere in a past ASRC,
IASA, or other publication that would be possible to reference?

There is certainly a great deal of extremely valuable "tribal"
knowledge that gets passed down among archivists and preservationists,
but it would be nice to have this captured somewhere.  The ARSC list
manages to capture some of this, although in an unstructured fashion.

Eric Jacobs
The Audio Archive


-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of George Brock-Nannestad
Sent: Friday, July 22, 2005 12:38 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] identifying lacquer disc substrates


From: Patent Tactics, George Brock-Nannestad

Hello, again,

I keep my ARSClist messages, so I went back to re-read what Eric Jacobs had
written originally about his mottled "glass" discs, to completely absorb the
description. And, please, can we try to use "lacquer" instead of
"acetates" -
it was not cellulose acetate but cellulose nitrate. Perhaps the expression
crept in because of the nitrate film scare.

----- I think that it is useful to look at a few parameters here. First of
all the stiffness of the disc itself. Here glass is the stiffest and has a
distinct "ping" when struck (antiquarian-dealer-wise) at the edge. Then
comes
aluminium, which mostly has a "pong" sound (smells professional, though).
Then comes something that has not been brought up yet on the list: zinc.
This
has a floppy feel to it, and striking it does not really create an
identifiable sound. Those that I have seen are thinner than the aluminium
ones.

----- the thickness is usually like this: glass thickest, then aluminium,
then zinc. However, I know of at least one exception - the Danish Solvpladen
(also discussed somewhere by Michael Biel), which is a very thin bright
aluminium disc with light yellow gelatin-based coat.

----- identification of the type (in particular where the label looks as if
it could be a private pressing) I usually do at the centre hole: is it
metal,
i.e. aluminium or zinc, is it glass or cardboard. Or is it some pressing
material.

----- the worst records that I know used a zinc base, because those break
down in a very distinct pattern. Initially, when the zinc is bright, the
adherence of the lacquer is good, but the lacquer allows permeation of
oxygen, and the zinc surface corrodes into a grey that has virtually no
adhesion. Combined with a lacquer that dries out this gives a peculiar curly
peeling very different from the flaking that we know from aluminium and
glass. And to my knowledge irreparable damage.

----- getting back to the original question: I have never seen particle
board
like this, but if it is metal, then crystallization at the surface (or
different orientation of oxidation products) might give this impression. If
you calculate the volume of the item, subtract a cellulosic layer and weigh
it, then you would at least get an impression of its specific gravity.

----- another query:

> Do you think that the dard red, transparent record was solid
> nitrocellulose?  Or was it nitrocellulose on a glass substrate?

----- it pinged, so it was glass. Solid shellac would have been limp in
comparison - another clue that was overlooked.

Kind regards,


George