Glass changes little over time and is not affected by corrosive materials or even most acids. Weather affects glass windows, by causing the lead (in stained glass windows) or wooden frames to expand and contract. The temperature between the inside and outside of the building causes the strips of lead or wood to expand and contract by different amounts on the two sides of the window. After many seasons, the lead or wood weakens, and the glass begins to bulge. 

Lance Watsky
Preservation & Media Specialist
The Georgia Archives
5800 Jonesboro Road
Morrow, GA 30260
678-364-3764 (phone)
678-364-3860 (fax)
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-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of Bewley, Nigel
Sent: Friday, January 30, 2004 9:55 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] stability of shellac disks do we account for window glass that has become thicker at the
bottom of the pane than at the top?  Apparently glass 'flows' over time -
years not weeks - and window panes change shape!

British Library

-----Original Message-----
From: Don Cox [mailto:[log in to unmask]]
Sent: 30 January 2004 15:00
To: [log in to unmask]
Subject: Re: [ARSCLIST] stability of shellac disks

On 30/01/04, Art Shifrin wrote:
> "I have shellac records over a century old which exhibit no
> deterioration other than wear!
> Steven C. Barr"
> How do you know that the disks have not in some way changed or
> deteriorated?
> Yes, they're playable but even glass changes shape over time.

I saw an exhibition of Roman glass a few years ago. Those bottles etc
didn't show any signs of having changed shape over 2000 years.

Don Cox
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