Zum Thema Glas und Viskosität habe ich hier noch eine Stellungnahme gefunden, aus der MIT Vorlesung „Introduction to Solid State Chemistry“ , eine interessante Vorlesung übrigens.

https://youtu.be/kB2Ue4Fip2c?t=1374
This proves that glass is a solid.
There are many people out there, even in the popular press, who will say, glass is just a very, very viscous liquid.
Nonsense. Look at this. It has this coefficient of thermal expansion.
And don't fall for any of that nonsense they tell you when you go to the cathedrals in Europe and the glass is thicker at the bottom because it's been dripping for 400 years, and that proves-- … you know why the glass is thicker at the bottom? Because they made it by spinning.
And when they spun it, it was graded in thickness from the center out.
And now, if you're the glazier and you're putting the glass in a window, which way would you put a pane of glass that had variable thickness?
Would you put the thickest part up or the thickest part down?
It's thicker on the bottom because that's the way it was made.
Lord help the tour guide when there's an MIT student taking 3.091 on that tour.