Waves Found in Old Glass...

I had a very interesting conversation at today's show with a gentleman who explained to me the reasoning behind waves found in old glass - as it was explained to him by an older man who glazed windows for a living.  What was told to him was something like this: waves in old glass are found because the molecules in the glass are always changing so over a long period of time - these waves appear, etc.

I was so interested in what he shared with me I decided to do a little research on the topic this evening (since I can't sleep because of the storms).  What I read so far says that many believed that glass is a form of "liquid" and that over time the "liquid" shifts thus explaining why the consistency of old windows in old buildings are much "thicker" at the bottom - because over time the liquid has basically seeped downward.

THEN...I read that this is not true and is a  very common misconception. When in fact, waves found in old window glass are a result of their manufacturing process. Additionally, the window panes that were thicker at the bottom were due to the installers actually hanging them so the thicker part of the pane, or heavier part of the window, was placed at the bottom. Again, the inconsistancy in the glass thickness was due to how it was "manufactered" at the time.

So, thank you to the kind gentleman who stopped by my booth today and shared such interesting information with me! It's really sparked a whole new interest for me - finding out more about how old glass was made!  Thanks you! :)