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Re: [ARSCLIST] stability of shellac disks
On 30/01/04, Bewley, Nigel wrote:
> Okay...how 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!
Do they? I have always lived in old houses, and I haven't seen windows
that are thicker at the bottom. A lot of old glass is very uneven and
gives distorted images. It is so long since glass of that poor standard
was sold that I think by now any still in place would have flowed.
It is perfectly true that glass is non-crystalline, so physicists call
it a super-cooled liquid. However, its viscosity is so high that flow is
not apparent after thousands of years.
If you make a glass knife blade (for cutting electron microscope
sections), it stays sharp. If the glass was flowing, it would lose its
edge.
Regards
--
Don Cox
doncox@xxxxxxxxxxxxxx