NYTimes on the science of glass…
It is well known that panes of stained glass in old European churches are thicker at the bottom because glass is a slow-moving liquid that flows downward over centuries. COMPLEX Glass in sheet and molten forms. Glass transition differs from usual phase transition.
Well known, but wrong. Medieval stained glass makers were simply unable to make perfectly flat panes, and the windows were just as unevenly thick when new.
The tale contains a grain of truth about glass resembling a liquid, however. The arrangement of atoms and molecules in glass is indistinguishable from that of a liquid. But how can a liquid be as strikingly hard as glass?
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Then why do we not see old glass with the thicker parts at the top or on one side or the other?
Because when a window slams shut, the thick part at the top would break the thin part at the bottom, smart guy.
glass is not a liquid, it is an amorphous solid.
http://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass
The reason the thicker portion isn’t at the top is that they would intentionally put it at the bottom for stability.
Thanks for addressing this. The last ten years I’ve been waiting for the rose window to drip to the floor of Chartres. I hope it won’t come to pass.