Glass Like Water: Fact or Fiction in Antique Windows

A blog post by Karen Bishop, Archaeology Intern

One of the first things I noticed walking into the main floor of the Lloyd Street Synagogue were the windows. Not the colorful, glowing, starburst-patterned stained glass windows above the ark, but the rippled square windows on the side walls. Whenever I see antique glass I always think, “wow, this building is really old,” and I feel like a lot of other people have that thought, too. The appearance of old windows has always fascinated me: the variance in transparency and wavy patterns look like a suspended liquid. In fact, I was always of the belief that glass actually was a liquid. That’s why the bottom of stained glass in medieval cathedrals is thicker than the top, and why centuries old homes have river-like patterns running down the windows. When I went to research the liquid properties of glass to explain the appearance of the LSS windows, however, I found out that glass is in fact not a liquid, this is just a myth. 

The truth is that if you were to examine the thickness of cathedral glass or appearance of home windows when they were installed hundreds of years ago, you would make the same observations. The variances observed today are simply a result of the methods used to make glass ‘back in the day’. Glassmakers used hand-blown techniques that made it impossible to achieve a perfectly smooth, even texture. Glass is noticeably thicker at the bottom likely because it was easier to install it that way. However, there is some truth to the thought of glass being a slow moving liquid. Glass is an amorphous solid: when molten glass cools, the molecules retain the random patterns of the liquid state, but the bonds formed are strong, like that of a solid. The nature of glass still baffles scientists, though, so it’s no surprise this myth is so widespread.

If you would like to know more about the nature of glass and the exciting debate about it within the realm of scientific research (because I know you all do!), you can read the New York Times article The Nature of Glass Remains Anything but Clear.