The AFU and Urban Legend Archive Science Glass Flow glass impurities 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: David.Bloomberg@f2112.n2430.z1.fidonet.org (David Bloomberg)
Date: 15 May 95 12:35:05
Newsgroups: alt.folklore.urban
Subject: Re: Old windows thickening at the base?

In a msg to All on <May 09 14:30>, Ray Depew of 1:2619/599 writes:

RD> : Colored panes of glass have significant amounts of metallic impurities, RD> : which can create more ordered crystalline structure in the glass.

RD> Whoa, wait, back up. "Metallic impurities?" You mean salts of gold, RD> copper, sodium or cobalt? Okay. Let's add some of those "metallic RD> impurities" to other liquids. Take molten metal, for example, or molten RD> sodium chloride, or even plain old water. Add a handful of copper RD> sulfate. Now, lower the temperature. Is the "freezing point" higher RD> or lower than it was before?
RD> It's lower, right? So we could say that adding impurities to the RD> liquid lowers the freezing/melting point. That's freshman chemistry.

Sorry, Ray, but glass science is anything BUT "freshman chemistry." Considering the impressive-looking signature you ended this message with, I'm quite surprised you would make such a statement. When you add those things to water, they don't modify the structure in a way which may either strengthen or weaken the bonds overall -- that's because glass is NOT simply a liquid -- it is an amorphous _solid_.

RD> Hence, the impurities in stained glass should lower the glass RD> transition temperature of the glass, making colored glass flow MORE RD> easily than regular glass, right?

Not necessarily, no. Some impurities raise the glass transition temperature, some lower it.

RD> Your suggestion about "more ordered crystalline structure in the glass" RD> is meaningless if you insist that glass is an "amorphous solid". RD> Either it's amorphous, or it isn't. The "metallic impurities" do not RD> impart a crystalline structure to the glass; by your own definitions, if RD> they did, it would cease to be a glass.

It is amorphous in long-range order, but its short-range order may become "more crystalline" as he has said. Perhaps he could have better phrased it by saying that the bonds would become stronger.

RD> : Keith Gerritsen, a student of Materials Science and Engineering

RD> Ray Depew, BSChE, MSEE, amateur mineralogist and geologist, working in RD> chemical engineering and materials science for nigh onto 14 years

David Bloomberg, BS Ceramic Engineering, Did Master's project on the varying effects of additives to phosphoborosilicate glasses (haven't finished writing thesis).

From: rrd@fc.hp.com (Ray Depew)
Newsgroups: alt.folklore.urban
Subject: Re: Old windows thickening at the base?
Date: 18 May 1995 16:53:54 GMT

David Bloomberg (David.Bloomberg@f2112.n2430.z1.fidonet.org) wrote: : In a msg to All on <May 09 14:30>, Ray Depew of 1:2619/599 writes:

: weaken the bonds overall -- that's because glass is NOT simply a liquid -- it
: is an amorphous _solid_.

: RD> Hence, the impurities in stained glass should lower the glass
: RD> transition temperature of the glass, making colored glass flow MORE
: RD> easily than regular glass, right?

: Not necessarily, no. Some impurities raise the glass transition temperature,
: some lower it.

Cool. So the previous poster was correct in stating that colored glass (*some* colored glass) could have a higher Tg. Can you give us an educated guess about some of the additives in colored glasses? For example, gold salts (red glass), cobalt salts (blue), copper (blue and green) and iron-I-think (yellow/brown)?

I stand happily corrected by someone with more real knowledge on the subject. Speaking of which:

: David Bloomberg, BS Ceramic Engineering, Did Master's project on the varying
: effects of additives to phosphoborosilicate glasses (haven't finished writing
: thesis).

Maybe *you* can definitively answer the question for us -- okay, three questions:

(1) As an "amorphous solid," does glass flow?

(2) What's the "flow rate" of glass at room temperature?

     (Okay, assume a pane of ordinary soda-lime window glass, mounted
      vertically in a frame.  The only force acting on it is its own
      weight -- gravity, if you will.)

(3) What evidence of this "flow" would we be able to see over, say,

     a few centuries?
     (No micrometers or calipers here.  We want things like:  bulging
      at the bottom; voids; weeping; dendrites or nodules; oozing out 
      over the frame.  You know, stuff that can be easily observed with 
      the unaided senses.)

Regards
Ray "will defer to anyone who writes their thesis on glass" Depew rrd@fc.hp.com