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[ARSCLIST] Glass Records and gelatine

While we're all thinking about glass lacquers:

I know that not all glass discs have gelatine lacquers (most are cellulose nitrate), but do all gelatine lacquers have a glass substrate? I was told this once and have never seen any evidence to contradict it, but as a rule it seems suspiciously simple. 

The distinction between nitrate and gelatine is an important one to make, as a gelatine disc will blister like crazy if it's wet-cleaned. 



-----Original Message-----
From: Association for Recorded Sound Discussion List on behalf of Eric Jacobs
Sent: Wed 5/28/2008 17:55
To: ARSCLIST@xxxxxxxxxxxxxxxx
Subject: Re: [ARSCLIST] Glass Records
On Wednesday, May 28, 2008 8:20 AM, Marcos Sueiro Bal wrote:

> Of 1,925 with metal substrate, 375 have evidence of palmitic acid (19%). 
> Of 123 glass-based, 22 have evidence of palmitic acid (18%).

I would venture to guess that the severity of the PA on the glass 
substrate discs would be less so than on the metal substrate discs
(assuming that both types of discs were stored under similar 
conditions).  That's been my experience at least.

Glass is an insulator, and metal is a conductor.  This means that
metal will respond to temperature fluctuations more rapidly than
glass, subjecting the laminate to wider and more rapid temperature
fluctuations.  It is these temperature fluctuations that cause the
exudation of the plasticizer, which then leads to the PA formation.
Thus the metal based discs will exude more plasticizer than the
glass based discs under identical circumstances.

Eric Jacobs

The Audio Archive, Inc.
T. 408.221.2128
F. 408.549.9867

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