Many years ago, I encountered a glass engineer and his wife, a ceramic engineer, in my studio/gallery. One of our topics of conversation was on glass myths. One of the most common myths people talk about is the one about stained glass windows in Europe slowly melting due to being thicker at the bottom. If the glass really was moving, don’t you think all those Ancient Egyptian glass relics would be puddles by now? The reason the windows are thicker at the bottom, is because of the way flat glass was made back then. Glass windows date back to Ancient Roman times. A bubble was blown, puntied, then spun open flat, using centrifugal force. The center of the rondel, or disc, was naturally thicker. A lot of you may have seen small round glass pieces like bulls-eyes to make a window. Artisans using the glass would then design and cut the glass, constructing a window with the heavier pieces at the bottom for support. FYI: at 777 °F glass would move a visible amount in 800 years, yet at room temperature, it would take longer than the age of the universe. In other words, it doesn’t move!
Glasses are amorphous solids, not liquid
This is an interesting piece of information I found at http://dwb4.unl.edu/Chem/CHEM869A/CHEM869ALinks/www.ualberta.ca/~bderksen/florin.html. Structurally, glasses are similar to liquids, but that doesn’t mean they are liquid. It is possible that the “glass is a liquid” urban legend originated with a misreading of a German treatise on glass thermodynamics. Glasses are amorphous solids that will flow only when liquefied at temperatures of hundreds of degrees centigrade. There is a fundamental structural divide between amorphous solids (including glasses) and crystalline solids. If glass was a solid, you wouldn’t be able to see through it. The materials used for glass-making cool to form an amorphous mix of molecules (like a liquid) and have electrons that do not absorb the energy of photons in the visible spectrum. This is why you can see through glass, but not wood, metal or stone, which are all solids.
“Don’t inhale on the pipe!”
Another myth I get asked a lot is that you can inhale hot glass on the pipe. If I blow a glass bubble on the pipe, then suck in, the bubble collapses. It is not viscous enough to flow up the pipe. Also, the pipe is about 5 feet long. Consider this: it takes a lot of effort to draw a thick milkshake up a short straw… hmmmm. Maybe the “inhaling glass” theory is about the presence of silica dust or other chemicals around the glass studio. That would definitely be dangerous!