I live in New England. I've had the privilage of living in two 300+ year old homes. In my opinion one of the greatest charms of an old home, one that cannot be replicated, is its windows. They're always warped in the most interesting ways.

Assuming the disfigurment is indeed a product of time, and not of the poor production standards in the 18th century (I could be wrong), I'm fairly sure the reason windows warp is because glass is in fact a supercooled liquid, or some sort of amorphous solid. I'm a little patchy on the chemistry but you get the idea. Under the pull of gravity and over a long period of time, the molecules in a pane of glass move perceptibly.

If glass changes shape in a window, wouldn't it also change shape in a lens?

I ask this question because I wonder if the old lenses so desired by modern
wet-plate and alternative process photographers have changed their properties over time. Obviously many photographers enjoy vintage lenses, and use them often. But Eventually won't all lenses become merely nostalgic, and have no real value to a working photographer? Won't the characteristics of a certain lens from a certain period change over time?

-Alex