There was one person who brought in an old panes of glass that was thicker at one end than the other and said that “Here is proof that glass flows! It is a liquid!”
Well, What is Crown Glass?
Sorry! It was/is actually “Crown Glass”. And its different thicknesses are just a result of the old process of making window pane glass. They placed the thicker portion at the bottom during installation, which just makes it seem as though it “flowed” in the direction of gravity.
“(How to make Crown Glass:) Molten glass is gathered on a blowpipe, and a balloon shape is blown. The blowpipe is removed, a solid “punty” rod is attached and the glass is spun rapidly until a disc is formed. The outer portion beyond the central knob is then cut into panes. By the 18th Century quality was often very good with an almost unmarked fire-finished surface. Crown was the preferred choice for window glass, together with some imported Cylinder glass until the mid 19th Century.” – from (http://www.londoncrownglass.co.uk/London_Crown_Glass/Manufacturing.html)
For those interested some areas actually do have some of this glass still installed in some of its windows. I have changed out one that was broken and have seen the difference in thickness from one end to the other. It was actually very interesting to see. And no, we do not make glass here at our shop. We have no room for the bellows furnace and all the other required equipment!