The idea that glass after being formed is in a state of flux concerns the belief, held by many, that because glass is a "super cooled liquid" it actually has a degree of "flow" at temperatures within the human comfort range. This urban legend would have us believe that the windows in colonial homes and in very old stained glass windows are thicker at the bottom than at the top because glass is a "supercooled liquid" and is slowly flowing. Ahh that pesky gravity. The acceptance of that story is not based on fact but on a mythological story that has been circulating for many many years. (I read it on the internet so it must be true). There was a time, in the dim dark past that, in my ignorance I believed in the myth of glass flow. Without question I accepted the myth of glass flow. My blind acceptance of what I thought passed for fact should not be a trait of the curious mind. What could I have been thinking when I accepted the "fact" that the Rose Window would soon spill out of the confines of the lead cames that have held it in place all these years. Okay, lets get to the heart of the myth of glass flow, but before reading on do some research and look up the word "poise" and then when you understand what poise is then look up the poise of lead and glass. If you're still a believer in glass flow after that then Read On!
I was made aware of the fallacy of the glass flows myth many years ago by the late great glass chemist, Nick Labino. Nick offered this simple analogy, "...if the windows found in early Colonial American homes were thicker at the bottom than the top because of "flow" then the glass found in Egyptian Tombs should be a puddle." Wow, that was a shocker. And there's this one from Wikipedia, "If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes.
Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed". I just love real world examples! For those of you that are still skeptical I cite research that tells us that although 1/2 of the glass in old stained glass windows is thicker at the bottom, take three guesses where the other half are thicker and the first two guesses don't count. You got it, sides and top. Hmmm, what do you suppose that indicates? In other words, if glass flowed then ALL the glass in antique windows would be thicker at the bottom and research tells us that's not true. If you still don't believe it, read below what the brainiacs have to say. When that know - it - all antique dealer whips out the urban legend of glass flow, send him or her to this page. After they read all the information below and they still refuse to believe that glass doesn't flow have them email me with a reason other than "thicker at the bottom."
Finally, Dr. Neumann relates the following. Read this carefully: "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."
What Dr. Neuman and Labino is saying is that if glass flowed, all the glass that comprised antique windows should be thicker at the bottom, but we know that is just not true.
Authors note: In the real world glass is for all intents and purposes (in every practical sense) frozen in place but in the laboratory physicists are still at work proving that there is some movement as purported in this abstract sent to me by Dan Watts. The abstract is a real page turner.
By C. Wu
Does Glass Ever Stop Flowing?
©1996 Florin Neumann
How did the "glass is a supercooled liquid" urban legend originate? It is possible it began with an erroneous reading of an influential book by Gustav Tammann (1861-1938), a German physicist who was among the first to study glass as a thermodynamic system (Tammann, 1933). I was unable to locate a copy of Tammann's book to verify this, so the following is speculation. One or two papers I consulted attributed to Tammann the statement "Glass is a supercooled [or undercooled] liquid." But, from other papers, it appears that what Tammann actually wrote was "Glass is a frozen supercooled liquid" [my emphasis]. My speculation is that an author misquoted Tammann, and this misquotation was repeated by later authors who, since copies of Tammann's book are rather rare, did not refer directly to Tammann.
Until about 20 years ago supercooling a glass melt was the only way to obtain glass, and the behavior of melts as they passed through the glass transition (i.e., solidified) was very different from crystallization. But solid-state physics was almost entirely based on the study of crystalline solids, which made the behavior of glass melts appear paradoxical. To emphasize this a professor would state "Glass is a liquid which has lost the ability to flow", and some undergraduate, with his mind more on the Friday night date than on the physics of glass, would remember only "glass is a liquid"... Perhaps now we can finally put this legend to its well-deserved rest.
What does the Corning Museum of Glass have to say?
Glasses are amorphous solids. There is a fundamental structural divide between amorphous solids (including glasses) and crystalline solids. 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.
Now that you've gone through this page and still remain skeptical I would recommend you click on the link below and read up on the physics of the question.
Phillip Gibbs Link (This is a must read)
Download the file by clicking on the link below.
Send me your experiment and I will submit it to my board of certified rocket scientists for peer review. If they feel your experiment passes a rigid set of scientific standards I will post it to this site. Below are two experiments that have met our rigid standards and one observational sort of skeptic. I post them for your consideration.
Concerning the article "The "Glass Flows" Myth" I experimented (observed) that flat glass panels about 1 meter long horizontally adjusted on the top of an aquarium end up after about a few months with about half a centimeter sag on the middle part, after that the curvature could be observed whatever the position and could be reversed with a few months up side down! Temperature was sometimes going up to about 50 or 60 degree Centigrades because of the close proximity of the artificial UV lights. So from then flowing glass was not so strange to me, and I think cathedrals have special conditions :
1. Dark glass exposed to the sun can probably heat up a lot, may be 90 degrees C. (*a)
2. Being surrounded with dark lead would increase the heat.
3. The pressure on the bottom pieces could be very important because of lead flexibility and because of the great height of some stained glasses. Otherwise where does the 10 power 32 number came from? Otherwise, it would be very interesting to see some viscosity curves depending on temperature and pressure, I guess the glass viscosity for ambiance temperature could be interpolated
(*a) in fact if very dark south exposed glass panels get more asymmetric that the clear north exposed we'll get an interesting clue.
I wonder how they feel about Global Warming and Evolution?
Editors note: What I want to know is what else he stores in the back of his toilet and what was that pipette used for anyway!
Otherwise, feel free to add me to the unofficial short list of skeptics who've emailed you but please don't quote me on the subject as this is just a friendly email and a note of appreciation for the information provided. Thank you!
Kind Regards and Best Wishes,
Editors note: This is really a good one. Would love to know what churches and farm houses. What I find most interesting is that he has seen this phenomena in more than one church and more than one farm house.