A Reminder About Camera Lenses

[kamagong]

I don't know if I buy that glass is a liquid theory. I've seen ancient Egyptian and Greek glass. If it were a liquid, how come the bottles weren't puddles after 4,000 years?

Chad

Many of the stained glass windows in European cathedrals have panes that are noticeably thicker at the bottom than they are at the top.

 

[65535]

I think the thing is that glass flows at higher temperatures rather than melts like most materials. So it's amorphous, at room temp it flows so incredibly slowly you would never know it in a couple of lifetimes, maybe in centuries and millenia.

 

[Karda]

Many of the stained glass windows in European cathedrals have panes that are noticeably thicker at the bottom than they are at the top.

The Antique Windowpanes Story

The question of antique windowpanes has been addressed by Plumb, 1989[2]. He noted the following:


[...W]hy are the panes of antique window glass thicker on the bottom than the top? There really are observable variations in thickness, although there seem to have been no statistical studies that document the frequency and magnitudes of such variations. This author believes that the correct explanation lies in the process by which window panes were manufactured at that time: the Crown glass process.
In other words, while some antique windowpanes are thicker at the bottom, there are no statistical studies to show that all or most antique windowpanes are thicker at the bottom than at the top. The variations in thickness of antique windowpanes has nothing to do with whether glass is a solid or a liquid; its cause lies in the glass manufacturing process employed at the time, which made the production of glass panes of constant thickness quite difficult.

 

[LUW]

Yeah, if that is true, every big ass optical telescope in the world would be useless in a few years because they don't spin the lenses around every now and then...

 

[Samael]

I think we can pretty safely say "myth busted."