Just to give some additional background - that probably added to the urban myth about the 'flow' of glass.
Anyone who cuts glass with a dry diamond (which my wife - a picture framer - does on a daily basis) knows that - having made the scratch - the glass will break easily by flexing the glass along the scratch - provided that one does not wait around too long. The reason given for this - contrary to all the heavy scientific evidence already provided - is that the diamond makes a perfect V-shaped scratch. But in a relatively short time - and at a molecular level - the glass rapidly anneals/flows to round-off the crisp bottom of the V. This makes it much more likely that the glass will not crack along scratch. My wife scores the glass and immediately flexes it : it parts perfectly every time. A thing I cannot emulate myself…. To get around this problem, many less handy glass cutters prefer to use a wet diamond cutter. These cutters have a little reservoir of kerosene that wets the scratch made by the diamond which slows the degradation of the V, and allows more time to make the break. Wet diamond cutters are supposed to last longer than dry ones. But, in the picture framing business, one does not wish to have the extra stage of cleaning kerosene smears off the glass, as well as the usual fluff/insect stains/finger prints. (Interesting how this gnomonic list gets off topic - but long may it continue.) Best regards Kevin Karney Freedom Cottage, Llandogo, Monmouth NP25 4TP, Wales, UK 51° 44' N 2° 41' W Zone 0 + 44 1594 530 595 On 10 Aug 2011, at 01:18, John Pickard wrote: > Good morning all, > > The (alleged) flow of glass in old windows is covered by Jearl Walker in his > excellent "The flying circus of physics" 2nd edition, ISBN 978-0-471-76273-7 > on p. 105. > > Walker provides a number of references on his website > (http://www.flyingcircusofphysics.com/) (Click on link to Chap 2, and scroll > down to item 2.57 Flow of medieval cathedral window glass). > > Here are the references listed by Walker. > > 2.57 Flow of medieval cathedral window glass > This item is discussed in the book The Flying Circus of Physics, second > edition, by Jearl Walker, published > by John Wiley & Sons, June 2006, > The material here is located at www.flyingcircusofphysics.com and will be > updated periodically. > Comments > References > Dots through indicate level of difficulty > Journal reference style: author, title, journal, volume, pages (date) > Book reference style: author, title, publisher, date, pages > Newton, R. G., “Fact or fiction? Can cold glass flow under its own weight > and what happens to stained > glass windows?” Glass Technology, 37, No. 4, 143 (1996) > Zanotto, E. D., “Do cathedral glasses flow?” American Journal of Physics, > 66, No. 5, 392-395 (May > 1998) > Zanotto, E. D., and P. K. Gupta, “Do cathedral glasses flow? --- > Additional remarks,” American Journal > of Physics, 67, No. 3, 260-262 (March 1999) > Stokes, Y. M., “Flowing windowpanes: fact or fiction?” Proceedings of the > Royal Society of London A, > 455, 2751-2756 (1999) > Stokes, Y. M., “Flowing windowpanes: a comparison of Newtonian and > Maxwell fluid models,” > Proceedings of the Royal Society of London A, 456, 1861-1864 (2000) > > > While I can't offer any professional opinion on the evidence for flow or > urban myth, I have found Walker's book a great source of all sorts of arcane > information fully supported by documentation. It's also a great source of > information for high school physics etc. assignments! This is the sort of > book that shows how science is completely integrated into society. It's a > pity that such clear writing is not used in high schools to turn kids on to > science and physics. After all, how many of them know that planes are "kept" > in the air by Bernoulli's principle? And the same principle is responsible > for sand dunes etc. (I guess I'm preaching to the converted in this sundial > list!) > > Cheers, John > > John Pickard > john.pick...@bigpond.com > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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