From: email@example.com (Terry Chan)
Subject: Glass Flow [Was Re: OBJECTIONS to afu faq (v.2.50 1/194) ]
Date: 30 Jan 1994 04:15:56 GMT
As part of a series of off-the-cuff objections to various
points in the FAQ, cee1@Ra.MsState.Edu (Charles Evans)
objected to the following:
RE "F. You can see glass flow in the windows of old buildings."
>I will have to disagree.. in (at least) the Old Wavery Mansion
>near Columbus, MS
[...details involving information from a "Lady" deleted...]
>I had heard/seen that before I learned in school that glass is
>amorphic (no crystals.. right).. just very very viscous "but
>would flow over time".. always stuck in my mind.
Others, such as prolific poster boy firstname.lastname@example.org (David
"Soon to be a Pud Boy Near You" DeLaney) cautiously casts his lot
against the FAQ and writes:
>This discussion I wasn't around for the first time; I will put my
>1.87 cents in on the T. side, as I'm pretty sure I've *seen* very
>old, wavy windows at several points.
Well, since Punk Papai's credibility may have been eroded
somewhat since he didn't request address and plane fare
when he had the opportunity, I dug some junk of out my
files and present the following.
In a 4 Oct 1993 post, surprisingly informative poster (for
someone who's affected by Coriolis as much as those in Oz
are) email@example.com (G. Paul Savage) gave some
>By the same token, this does not mean that
>we can observe the flow of glass by simple
>empirical methods such as looking at the
>thickness of window panes. See for example
>the following: "Antique windowpanes and the
>flow of supercooled liquids" by Robert C.
>Plumb (Worcester Polytech. Inst.)in the Journal
>of Chemical Education, 66(12), 994-6, 1989.
Paul provided the abstract of that paper, which read:
In an attempt to dispel the notion that colonial window panes are
thicker at the bottom than at the top because the glass is a
supercooled liq. that has slowly flowed downward over the hundreds
of years since it was installed, a discussion is presented on the
properties of glass. A historical account is also given on the
manuf. of window pane glass using the Crown glass process which
produced glass of fairly uniform thickness.
Now, this may have no meaning to some parties, so Paul dug out
the paper and summarized it in the following post:
>From: firstname.lastname@example.org (G. Paul Savage)
>Subject: Re: Non-flow of glass - final proof
>Date: 4 Oct 1993 23:52:12 -0500
>Organization: UTexas Mail-to-News Gateway
>Xref: dog.ee.lbl.gov alt.folklore.science:8135 alt.folklore.urban:94929
>In article <199310050310.AA25843@shark.mel.dit.csiro.au>, I write:
>>I will try to get hold of the full paper and relate its findings.
>And indeed I have. Some interesting points arise in the article "Antique
>windowpanes and the flow of supercooled liquids" by Robert C. Plumb
>(Worcester Polytech. Inst.)in the Journal of Chemical Education, 66(12),
>1)Robert Brill of the Corning Museum has records of the stories
> [of window panes 'flowing' over the years] dating back sa far
> as high school chemistry class in 1947. [surely enough to qualify
> as UL]
>2)The glassy state resembles a liquid in having short-range [molecular]
> order without long-range order ,but differs in that the entire network
> is rigid, whereas in the liquid state enough energy is available to
> break and reform bonds continuously.
>3)The temperature at which a rigid glass becomes a supercooled liquid is
> called the glass transition temperature, Tg. For window glass, Tg
> (measured) is 550 degrees C. For the limiting case of infinite time
> the thermodynamically calculated ideal glass transition state Tg(0)
> for window glass is 270 degrees C. For Pyrex the values are 550 and
> 350 deg., respectively. [This allone should be enough to put to rest
> any argument for the liquid properties of glass at room temperature
> (which rarely gets above 50 degrees C).]
>4)If a rod of glass is twisted it will return to its original shape.
> If it is twisted and held for a period it will retain its twisted
> shape BUT will gradually return to its original zero-twist state over
> time. This 'delayed elastic recovery effect' is explained in the paper
> but is too technical to go into here. Suffice to say, this experiment
> debunks any 'deformation of glass under pressure = glass flows' type
>5)Those who are convinced that glass flows like a viscous liquid under
> its own weight sometimes cite the Corning Glass Co. instructions
> printed on boxes of tubing, "Lay flat, do not stand on end". According
> to R. Lemker (Operations Manager, Fallbrook Plant, Corning Glass,
> Corning, NY) the instructions are to avoid damage to the ends of the
> tubing, not to keep it from sagging.
>6)The paper then goes into a long discussion of how glass windows were
> manufactured in the 1800's (the Crown glass process) and essentially
> comes to the conclusion (already offered in AFU) that antique window
> panes are thicker at the bottom because of variations in the thickness
> of the glass (which at the time were less important than other defects
> such as blisters, dust, lines, curves and scratches) produced during
> manufacture. The author surmises that glaziers would tend to put the
> thick end of the glass at the bottom for stability.
>Okay, does that end the issue? One thought mentioned at the end of the
>paper was interesting. If someone could find a copy of a window glazier's
>instruction book from the 1800's there might be mention of putting the
>thick end of the pane at the bottom. That would be conclusive evidence.
>email@example.com ....................... Australian Science
>CSIRO, Division of Chemicals & Polymers ................. Australia's Future
Terry "so I went ahead and built that glass house" Chan