Re: [Killietalk] Siphon

["Stan Perkins" <stanperkins at academicplanet_com>]

I have had archaeologists discuss aging of plate glass based on the ripples
and sagging of the glass. Could it be that older glass had more of a
tendency to flow than the modern product?  Anyone from Corning out there?

Stan Perkins
----- Original Message ----- 
From: "Hladky, John" <John_Hladky at tdytsi.com>
To: "'killifish discussion list'" <killietalk at aka_org>
Sent: Tuesday, January 20, 2004 3:10 PM
Subject: RE: [Killietalk] Siphon


> Thanks Wright, very interesting.
>
> I learned about "flowing glass" in a physics class during my undergraduate
> work.  The prof went on to say that mirrors in large, old telescopes have
> become slightly deformed leading to fuzzy images.  I wonder what it is
about
> human nature that make us gullible enough that such a myth would so imbed
> itself in our minds that even a physics professor, who should know better,
> would spread the story before checking it out.
> John Hladky
>
>
>
> -----Original Message-----
> From: Wright Huntley [mailto:whuntley at verizon_net]
> Sent: Tuesday, January 20, 2004 2:52 PM
> To: killifish discussion list
> Subject: Re: [Killietalk] Siphon
>
>
> John,
>
> Hladky, John wrote:
>
> > Chris,
> > It is common knowledge that glass, being an amorphous solid, actually,
> given
> > time, flows...
>
> Pure myth. Amorphous and solid, but no flow.
>
> >
> > WOW!  I don't want to open that can of white worms again.  I still have
> > heartburn from the crow I ate last time I brought it up.  Hey, this
would
> > make a great episode for "Myth Busters"!!!
>
> Agreed. Here I come. :-)
>
> I ran the precision glass shop at Hewlett Packard.
>
> I then ran a company for 30+ years that made precision glass scales. One
> of my customers built them into an optical-disk-mastering machine with a
> precision and repeatability of 40 nanoinches (one nanometer). We knew
> glass was stable and did not flow.
>
> To the best of their ability, the researchers at Ferranti found that
> unstressed glass was more stable than our knowledge of the velocity of
> light, back in the 60s. Because it is amorphous and doesn't undergo the
> same crystalline phase changes of metals, it is about the most
> physically stable substance known to man. It took many years to learn
> how to nitride and grind metallic gage blocks so there was enough
> external skin compression for them to be as stable. Until then, they
> used to shrink at a rough rate of 1 microinch per inch per year and
> required constant recalibration or certification.
>
> When very old plate-glass windows (actually early float glass, I think,
> that had then been ground and polished) were examined, the bottom edge
> was always considerably thicker than the top edge, so some naive
> reporters assumed the glass had slumped over the years. It turns out
> they didn't know diddly. The glass was deliberately made that way, for
> it made for a stronger, lighter store window to have the bottom edge,
> carrying the weight, thicker.
>
> > John in Huntsville
> >
> > -----Original Message-----
> > From: Chris [mailto:cgraseck at optonline_net]
> > Sent: Tuesday, January 20, 2004 1:01 PM
> > To: 'killifish discussion list'
> > Subject: RE: [Killietalk] Siphon
> >
> >
> >
> > What is it about old glass that makes it difficult to drill.  Has the
> > glass changed over time or is our modern glass less brittle.
>
> There are several answers to this question, Chris. Try cutting old glass
> shelves, for example. They are *made* very tough, with chemistry and
> edge shape, to resist breakage when you drop a medicine bottle on them.
> Getting a nice clean cut is very difficult.
>
> Old windows, through many years of daily temperature fluctuations tend
> to become better annealed and hence maybe tougher to cut. They often
> were made by grinding and polishing (plate glass) which could be tougher
> than float glass (most modern windows) to cut, too.
>
> There's probably no single reason, but generally old glass *is* probably
> a little harder to drill and cut (and easier to accidentally break in
> the process).
>
> Wright
>
> -- 
> Wright Huntley -- 760 872-3995 -- Rt. 001 Box K36, Bishop CA 93514
>
> "If people are basically evil, the last thing you'd want is a big
> government staffed by those evil folks exercising control over you."
>    -- David Bergland
>
>
>
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