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.
-John ============= >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] 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.. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
