[time-nuts] Lifetime of glass containers
jfor at quik.com
Mon Jun 15 21:34:21 UTC 2009
Interestingly, I recently had dinner with an archeology professor,
interested in the Etruscan period. She had just discovered a flatish piece
of glass i9n a dig, thousands of years old, and believes it was made
essentially like rolling out dough on a slab while red hot.
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com
>> [mailto:time-nuts-bounces at febo.com] On Behalf Of Dave Carlson
>> Sent: Monday, June 15, 2009 12:57 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Lifetime of glass containers
>> Not to charge in, but I've looked at ordinary window pane
>> glass in very old buildings and you can actually see the
>> rippling effect that occurred over time, showing the "flow"
>> of the glass toward the lower edge of the pane. One presumes
>> that the panes were relatively uniform when installed 120
>> years earlier. Sounds liquid to me.
> Nope.. 120 years ago, I don't think they had modern float glass or even
> continuous casting processes.
> You blew a large cylinder, cut it open, and laid it flat in an oven, or
> took molten glass, poured it onto a flat surface, rolled it flat, then
> polished it (with a "plate" hence the name "plate glass")
> Sometime early in the 1900's they started making glass in a sort of
> continuous casting process with slots or rollers or some such scheme to
> make sheets, but it wasn't very flat in an optical sense.
> After WW II, they developed the float glass process, where the molten
> glass is floated across liquid metal, giving you continuous production AND
> flat surfaces.
> So, what you're seeing in old buildings is the fact that flat glass was
> really hard to make and expensive. You might use it in a mirror, for
> instance, if you didn't use polished metal instead.
> I'm sure wikipedia has more than anyone would want to know about sheet
> glass manufacture..
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