I remember Waaaaay back at college getting told glass was a supercooled liquid. Maybe science has moved on since (or the lecturer was talking out his arse). Certainly the original windows in my house (circa 1860), the glass is thicker in the bottom than the top, so I ass-sumed that there was flow only over a very long period. But I've been humbled in this thread already so maybe I should just "step away from the keyboard"
More to do with how it was made then installed. Even church windows cannot show this due to the uneven finish.
