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That is a myth. The main reason very old glass is generally thicker at the bottom is that the manufacturing process produced glass with a thicker edge and was installed with that thicker edge at the bottom. It did not flow that way it was installed that way.

What Dr. Neuman and Labino is saying and is that if glass flowed, all the glass that comprised antique windows should be thicker at the bottom, but we know that is just not true.

That's a good way to get through high school, but by the time you hit your twenties, you should be viciously digging through Wikipedia on a daily basis. At least, that's what we do nowadays. I guess that wasn't so practical back before the invention of the encyclopedia.

...and I'm guessing you know the glass thing is false and those windows are actually thicker at the bottom because the glass was spun on a wheel. Centrifugal force caused the outer edge to get thicker. You can occasionally find the work of less thoughtful glaziers where the windows were installed upside-down. And it was a mediaeval cathedral, not just an old house!

Glass would deform in that time scale...

I'm guessing your talking about the urban myth that glass can flow and melt? Sorry, but glass doesn't melt, it would hold it's form as long as it isn't shattered.

Glass flow, read all about it. For your reading pleasure.

1. Solids can also evaporate, but they do so at a rate about 10^40 slower than say water, so it makes no sense to say that solids flow.
2. Glass does not flow, in fact it is about a billion times less viscous than lead http://www.cmog.org/index.asp?pageId=745
http://www.glassnotes.com/WindowPanes.html
3. Hydrogen cools when heated, per the Joule-Thompson effect. Search for the second instance of "James Dewar" http://www.hq.nasa.gov/office/pao/History/SP-4404/ app-a1.htm

And yooouuurrrreeee out!

Even glass flows.

See also this page debunking this urban myth

For the record, the idea that glass flows is an urban
legend

It's just the way it's made - glassnotes.Com

Quick note: glass is not a liquid. Read here http://www.glassnotes.com/WindowPanes.html

Twisted, I never said that all information should necessarily be free. I said all information will be free. Not because I think it it's pretty nifty how I don't pay anything, but because millions and millions of people will think it's pretty nifty how they don't have to pay anything.

Now, just because an artist won't be able to charge for every single time someone listen to his song, doesn't mean he won't be sponsored or making money in any way. Trust me. People will find a way to make money in any way possible.

The Sims Resource is a website with thousands upon thousands of different custom made objects for The Sims and The Sims 2. You can get 99% of all those objects for free on the internet, but instead, thousands(maybe more) of people have subscribed to this system because it's fast, convenient, easy to use, gives them the results they need. So, there will always be people that find niches in the economy and will profit from it. Once the music distro/publishing companies are gone, something else will take up the niche. What? I don't know.

No one ever asked movie companies to give out free backup copies. What we want is to not get sued or put in jail if we copy a DVD, or rip it to an mp4 on our laptop to take on vacation, or do any number of things with the DVD we just bought.

Bascially, we'd like to be treated the same as when we buy a set of glasses: once, we've bought it, we can do anything we want with it. Glassmakers don't try to have people put in jail for post articles on how to blow glass.

Furrfu!

(Or have I just been trolled?)

Glass flowing is a myth.

Old glass manufacturing technics were VERY imprecise. You might end up with a pane that had a thicker edge, in which case you would naturally put it on the bottom for balance.

Or you might end up with fairly uniform edges but have an irregular surface that looked like it was "flowing" but was static. I have picture windows in my house that are about 70 years old that have this "flow" pattern and have had people remark that the liquid must be pooling ... it's simply irregular hand-made glass.

Even if glass -does- flow (see the "a" link at the beginning), math shows it would take millions of years to complete the process, meaning no glass made by man would yet show visible signs of deterioration.

And you're right, "glassy" in this case is about the physical structure of the metal, not the light transmitting/absorbing aspects though those are probably mildly affected (I imagine a glassy steel will hold a shiny polish better than a crystal steel).

But I've seen cathedral windows that weren't just a different thickness at the bottom, they were sagging open at the top!

On the other hand, as one of the links points out, you can disprove the theory by simple mathematics.

Cathedral window age = 500 years
Cathedral window sag = 1 cm
Theoretical sag rate = 500 years/cm

Egyptian/Greek/Whatever glass vessel age = 3000 years
Theoretical sag rate = 500 years/cm
Expected sag of 300 year old glass = 6 cm

As the link notes, if glass flowed over time, all the old glassware in museums would show definite signs of puddling -- even taking into account differences in formulae. At the very least, the broken edges would have smoothed themselves like ripped-apart Silly Putty.

I wasn't convinced until I read the link. I had completely bought into the sagging glass idea!

Here's an alternate theory for the cathedral glass. When the window was made, using old-school techniques, they ended up with some imperfect pieces. Do you put those at the bottom, where the bishop will see them... or put them at the top, and let God decide if He cares?

Check youre windows, you will find they are larger at the bottom as it drips.