The AFU and Urban Legend Archive Science Glass Flow debunking cites ian Select a topic - - - - - - - - Home Searches AFU FAQ - - - - - - - - AFU Animals Books Celebrities Classic Collegiate Death Disney Drugs Food GIF Language Legal Medical Misc Movies Politics Products Religion Science Sex Songs TV - - - - - - - - Other sites

From: iayork@panix.com (Ian A. York)
Newsgroups: alt.folklore.urban
Subject: Re: Glass Flows!
Date: 6 Apr 1997 16:31:07 -0400

There is an article by Florin Neumann at <http://www.ualberta.ca/~bderksen/florin.html> which cites in its
debunking of this legend the following references:

Doremus, R. H. (1994) Glass Science, 2nd Edition. John Wiley & Sons, New York, 339 pp. ISBN 0471891746.

Elliott, S. R. (1994) Amorphous Solids: An Introduction. In: Catlow, C. R. A. (eds.), "Defects and Disorder in Crystalline and Amorphous Solids", NATO Advanced Studies Institutes Series; Series C, Mathematical and Physical Sciences, 418, Kluwer Academic Publishers, Dordrecht: 73-86. ISBN 0792326105.

Feltz, A. (1993) Amorphous Inorganic Materials and Glasses. VCH Verlagsgesellschaft mbH, Weinheim/VCH Publishers, New York, 446 pp. ISBN 3527284214/1560812125.

Gutzow, I. and Schmelzer, J. (1995) The Vitreous State: Thermodynamics, Structure, Rheology, and Crystallization. Springer Verlag, Berlin, 468 pp. ISBN 0387590870.

Jeanloz, R. and Williams, Q. (1991) Solid-State Physics: Glasses Come to Order. Nature, 350: 659-60.

Pfaender, H. G. (1996) Schott Guide to Glass, 2nd Edition. Chapman & Hall, London, 207 pp. ISBN 0412719606.

Plumb, R. C. (1989) Antique windowpanes and the flow of supercooled liquids. Journal of Chemical Education, 66(12): 994-996.

Rawson, H. (1991) Glasses and Their Applications. Royal Institute of Metals Book, Royal Institute of Metals, London, 499: 166 pp. ISBN 0901462896.

Tammann, G. (1933) Der Glaszustand. Voss, Leipzig, 123 pp.

One of those references (Antique windowpanes and the flow of supercooled liquids. Robert C. Plumb. The Journal of Chemical Education 66(12), 994-6, 1989) is available in full at
<http://www.ualberta.ca/~bderksen/windowpane.html>). It in turn cites
other peer-reviewed refences in its debunking:

1. Tolman, C.A.; Jackson, N. B. In Essays in Physical Chemistry; Lippincott, W. T. Ed.; Am. Chem. Soc.: Washington, DC, 1988; Chapter 3.
2. Ernsberger, F. M. In Glass: Science and Technology; Uhlmann, D. R.; Kreidle, N. J., Eds.; Acad.: New York, 1980; Vol. V, Chapter 1.
3. Slater, J. C. Introduction to Chemical Physics; McGraw-Hill: New York, 1939; p 456.
4. Douglas, R. W. Brit. J. Appl. Phys. 1966, 17, 435-448.
5. Hall, J. A.; Leaver, V. M. J. Sci. Inst. 1961, 38, 178-185.
6. Holloway, D. G. The Physical Properties of Glass; Wykeham: London, 1973; pp 131-143.
7. Muspratt, S. Chemistry Theoretical, Practical & Analytical as Applied and Relating to the Arts and Manufactures; Mackenzie: London, 1860; Vol. II, pp 21-216.
8. Chance, H. J. Soc. Arts 1856, 4, 222-231.

One of these references (Ernsberger, F. M. In Glass: Science and Technology; Uhlmann, D. R.; Kreidle, N. J., Eds.; Acad.: New York, 1980; Vol. V, Chapter 1.) explicitly says:

There is a widespread opinion that glasses are supercooled liquids and therefore have a finite viscosity at ordinary ambient temperatures. Stories are told of glasses flowing under their own weight: of ancient windowpanes that are thicker at the bottom; of glass that has sagged in storage. These observations must find other explanations, because glasses of commercially useful compositions are in fact rigid solids at ordinary temperatures.

More:

Glass is an amorphous solid. A material is amorphous when it has no long-range order, that is, when there is no regularity in the arrangement of its molecular constituents on a scale larger than a few times the size of these groups. ... A solid is a rigid material; IT DOES NOT FLOW WHEN IT IS SUBJECTED TO MODERATE FORCES. More quantitatively, a solid can be defined as a material with a viscosity of more than about 10^15 P (poises). --Doremus, Glass Science, 1973

The highest observed macro stress level acheived is only 20% of that, and was done to a glass fiber (as close to flawless as we can get). Therefore, we can not apply a yield stress to the glass that could cause it to flow without first breaking our sample. If, somehow, magically, you could apply a stress to an unflawed sample, then the observed plastic deformation (e2) would be roughly 1/15000 the magnitude of the applied stress (in kg/mm^2). So even if you could magically apply a yielding stress, then you would not be able to measure the deformation. This applies to glasses below 600C (or 270C for infinite time lengths). --Elastic-Plastic Problems, B.D. Annin and G.P. Cherepanov, c 1988, The American Society of Mechanical Engineers (paraphrased by Scott Sehlhorst)

We use glass in this case, not because it is transparent, but because its rigidity and permanence of shape are better than steel or concrete. --Preston, J. Appl. Phys. (13) pp623-654, 1942

1. "A glass is an amorphous solid which exhibits a glass transition"
2. "A solid is a material whose shear viscosity exceeds 10^14.6 poise" --Physics of Amorphous Materials_ by S. R. Elliott (London: Longman Group Ltd, 1983; ISBN 0-582-44636-8), from the definitions section, p. 5

There's only one article that even remotely supports your contention, and its very support actually refutes it, because it concludes that glass could only flow if several real-world considerations were ignored: ou'd have to have a piece of glass several miles long to observe any flow, and it would take several million years for the effect to manifest itself. They dismiss with a wave of their hands the objection that a piece of glass that huge would crumble under its own weight, destroying the evidence in much less than a million years . ("Gravity-Induced Flow of a Structural Glass at Zero Temperature", by Clare C. Yu and S. N. Coppersmith, from Journal of Non-Crystalline Solids, 131-133, 1991, pp 476-478). This is taken from Ray Depew's comments on the article; use DejaNews to find the whole thing.

Further, the claim that people make to support their contention--that old windows are thicker at the bottom--is trivially refuted, and so there is no evidence that glass does flow. Two people in the past couple of weeks in this thread have actually gone and looked at the windows in their old houses, or their old cathedrals. Stephen Tonkin <astro@aegis1.demon.co.uk> determined that "it is twaddle. In the
buildings I looked at many, but not all, of windows of uneven thickness have the thicker glass at the bottom. Some have it at the side. A few have it at the top." Charles Dimmick (dimmick@ccsu.ctstateu.edu) said "The south-facing windows of St. Peter's Church, Cheshire, Connecticut, built in 1840, have panes that undulate, as though they had flowed. The problem is that while most of the panes have undulations that would indicate downward flow, 1/6 of the panes have undulations that would indicate sidewards flow, and a few of the panes have undulations that would indicate flow at 45 degrees to straight down." They therefore agree with medieval stained-glass-window restorer Peter Gibson, who said that "in a lifetime of dismantling medieval glass [windows] he had seen hundreds of pieces that were thicker at the top."

This also agrees with the interpretation that the irregularity of the glass is due to the Crown glass manufacturing method, as described in (Muspratt, S. Chemistry Theoretical, Practical & Analytical as Applied and Relating to the Arts and Manufactures; Mackenz)ie: London, 1860; Vol. II, pp 21-216) by Sheridan Muspratt.

These are not all the references available that debunk this particular legend. You can find more at
<http://www.urbanlegend.com/science/glass.flow>.

The sci.physics FAQ at <http://www.weburbia.com/physics/glass.html> also debunks this legend.
--

      Ian York   (iayork@panix.com)  <http://www.panix.com/~iayork/>
      "-but as he was a York, I am rather inclined to suppose him a
       very respectable Man." -Jane Austen, The History of England

------- end of forwarded message -------