Here's a page that does an excellent job, in my opinion, of debunking that myth:
If the bottoms of old panes of glass are thicker, it's probably because they were fitted that way originally. Getting glass of uniform thickness is a relatively recent technology, I think.
Marty
Thank you, that was a well documented rebuttal and I stand corrected.
If you have a builders junk yard handy you can get one that has damage on one side only for virtually free
David - who found a door at the tip - just had a hole > I do the door thing. Cheap, and it works great.
You do?!? That self conflicting bit of tripe convinced you of something?
Yes. Here's another excellent site:
:"For definitive evidence that glass has not flowed in old windows we must examine the oldest examples. Early glass used to make bottles and windows was usually formed by adding soda and lime to silicates. Sometimes potash was added instead. Usually there were other impurities which made it softer than modern soda-lime glass. Other compounds were often added to give colour or to improve its properties. The Romans were making glass objects of this sort in the
1st century AD, and despite being very delicate, some examples remain--such as the elaborately decorated Portland Vase kept at the British Museum. Roman glassware provides some of the best available evidence that types of soda-lime glass are not fluid, even after nearly 2000 years. The oldest remaining examples of stained glass windows that remain in place have lasted since the 12th century. The oldest of all are the five figures in the clerestory of Augsburg Cathedral in Germany, which are dated to between 1050 to 1150. Many other early examples are found in France and England including the magnificent North Rose window of Notre Dame, Paris dating from 1250."There have been many claims (especially by tour guides) that such glass is deformed because the glass has flowed slowly over the centuries. This has become a persistent myth, but close inspection shows that characteristic signs of flow, such as flowing around, and out of the frame, are not present. The deformations are more consistent with imperfections of the methods used to make panes of glass at the time. In some cases gaps appear between glass panes and their frames, but this is due to deformations in the lead framework rather than the glass. Other examples of rippling in windows of old homes can be accounted for because the glass was imperfectly flattened by rolling before the float glass process came into use.
"It is difficult to verify with absolute certainty that no examples of glass flow exist, because there are almost always no records of the original state. In rare cases stained glass windows are found to contain lead which would lower the viscosity and make them heavier. Could these examples deform under their own weight? Only careful study and analysis can answer this question. Robert Brill of the Corning glass museum has been studying antique glass for over 30 years. He has examined many examples of glass from old buildings, measuring their material properties and chemical composition. He has taken a special interest in the glass flow myth and has always looked for evidence for and against. In his opinion, the notion that glass in Mediaeval stained glass windows has flowed over the centuries is untrue and, he says, examples of sagging and ripples in old windows are also most likely physical characteristics resulting from the manufacturing process. Other experts who have made similar studies agree. Theoretical analysis based on measured glass viscosities shows that glass should not deform significantly even over many centuries, and a clear link is found between types of deformation in the glass and the way it was produced.
Conclusion
"There is no clear answer to the question "Is glass solid or liquid?". In terms of molecular dynamics and thermodynamics it is possible to justify various different views that it is a highly viscous liquid, an amorphous solid, or simply that glass is another state of matter which is neither liquid nor solid. The difference is semantic. In terms of its material properties we can do little better. There is no clear definition of the distinction between solids and highly viscous liquids. All such phases or states of matter are idealisations of real material properties. Nevertheless, from a more common sense point of view, glass should be considered a solid since it is rigid according to every day experience. The use of the term "supercooled liquid" to describe glass still persists, but is considered by many to be an unfortunate misnomer that should be avoided. In any case, claims that glass panes in old windows have deformed due to glass flow have never been substantiated. Examples of Roman glassware and calculations based on measurements of glass visco-properties indicate that these claims cannot be true. The observed features are more easily explained as a result of the imperfect methods used to make glass window panes before the float glass process was invented."
...snip...
So how did that site convince you that glass is a solid ?
By the definition of terms, by the report of actual measurements made on medieval glass, by the sources used, and by the author's mastery of materials science.
Marty
I have the pretty much the set up you describe here. It works great, is relatively cheap, and the door is flatter than most other surfaces.
Jim W
And will continue so to do. Glass is classed as a "super cooled liquid" and will, albeit very very slowly, flow like a liquid.
Malcolm
Oh.
:-)
I guess the next thing is someone will say that rocks are not highly elastic
David
Boo wrote:
Thx, Dave.... I may have just found out why my rubber powered model is so damned heavy....
Bill
LOL!
Thanks for the laugh, qg.
Marty
The convincing parts of the analysis are that it is known that the methods used to produce some glass panes results in panes that have a thicker edge from the beginning. The person installing the panes naturally placed them in the window frames with the heavy edge down, resulting in the belief that the glass flowed over time. However, there have been panes found in some cathedrals, etc., in which the heavy edge is at the TOP, or on a side. That couldn't have been caused by flow.
Boo wrote:
Depends of which hemisphere they were in - if they were here in Oz then they were really hanging down and so...
David
ROFLOL!
David, It is comments like this, buried deep in the bowels of heavy discussions about something few know a little about, that makes this NG worthwhile.
I usually acoustic ceiling tiles that you can buy in 2 X 4 foot sheets very cheaply. They hold pins, can be cut, and are FLAT.
Malcom- that would be a -frozen- supercooled liquid, which is different than a liquid- read the reference referred to by M.X.M., above----
But I was going to add, that some small measure of "evidence" for the myth would be the contribution of any thoughtful and competent midieval glaziers- When installing an uneven piece of glass in a rectangular frame, it would appear to be the best practice to put it in with the thickest end toward the bottom- the better to support the weight of the glass above. Now when some modern tour guide or other semi informed individual comes along and observes this in the glass of some ancient building, it's only a short jump to the conclusion that the glass has flowed to this state. -Paul
SNIP
Oh no! 'They'" make it up as they go along there too!
You should realize that the "thoughtful and competent" should be able to make a flat piece of glass as well. And that the strength of the window as a whole is not significantly affected if the individual panes are put in thick side up or down.
Myth debunking DENIED!!!
Yay GLASS IS A LIQUID!!!
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