Glass does flow downhill, at least just a little bit. If you take glass tubing as is used in a chemistry lab and lie it down horizontal with supports only at the ends, after a month or so there will be a slight but distinct bow to the glass.
And many of the windows in my house are visually rippled, with more of the ripples toward the bottom, BTW, a glazier has told me that this rippled glass now sells vor at least $0.10 per square inch, with larger panes going for five and six times that much. People who want ultra authenticity in their renovations can get pretty crazy.
My front entryway has a lot of this, but the most interesting feature to the door is that it is not only not square it appears to have been made that way. When I first looked at it I realized it wasn't square and figured it had sagged. But upon closer inspection all nine pieces of glass, including the large central section, which is about 60 inches by 13, are skewed by about three degrees from square. Which makes them hmmm trapezoids? Actually, now that I think about it, it's more likely that the door sagged, caused the glass to break, and someone replaced the square glass with panes that were cut to fit. None of the sections of glass in the door itself are antique (and also none of them are safety glass, which means I should replace them with little kids around.)
