A short time ago, there was a toppic on, I think,GQ About glass, a liquid, sagging over time. Yesterday, my wife & I stayed in a hotel that was built in 1888. Though it has been up-dated, it still had many of the original glass panes. Close observation showed all to be thicker at the bottom than at the top.On some I saw definate sags on the horizonal imperfections.It seems to me that glass has a detectable sag in 100 yrs.
Zymurgist
Could have been blown glass that has imperfections and differences in thickness from thicker in the center to thinner on the outside during the blowing process. The workman putting the panes in the window might have intentionally put the thin sides of the pane at the top of the window. There were also bullseye panes from the center of the blow job that were sold to customers at a discount. Nowadays these bullseye panes are worth much more simply for their decorative effect.
this month’s Discover mag has an article on this issue - rejects the sagging glass theory; says that even if glass does sag, it would take thousands of years. Advances same argument as funneefarmer - until recently, the glass-making methods would produce irregular glass; it is only with modern “float” manufacturing methods that you get extremely regular glass.
I work with stained glass. This is just IMHO but glass, itself, doesn’t sag. A stained glass window will sag in time if it is not reinforced.
The individual pieces of glass do not bend or melt but the entire structure breaks down due to time and the fact that the lead pieces or foiled pieces let go. Oh, poo, this is hard to explain. It’s not the glass that is melting, it is the entire structure that holds the glass, that is sagging because it was not properly reinforced.
If you have seen clear glass windows with this sag then you are seeing really old rolled glass that had this defect to start with. I don’t care where you live but the temperatures just aren’t hot enough to get glass to slump. Unless you are Satan and are living in hell; THOSE fires might be hot enough to slump glass. But in your case; It was pained that way. Does that help?
Gosh, I hope so! I’ve done one window at 2’ x 3’ and reinforced it anyway, due to the inherent slumping of the materials that hold together the stained glass. It’s not the glass, it’s what is holding it together.