# Glass - liquid or solid?
**URL:** https://boards.straightdope.com/t/glass-liquid-or-solid/135210
**Category:** Cecil's Columns/Staff Reports
**Created:** [November 4, 2002, 1:53pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210 "2002-11-04T13:53:20Z")
**Posts on this page:** 13
**Page:** 3
### Author:  [@Scylla](https://boards.straightdope.com/u/Scylla)
#### Post date: [November 6, 2002, 7:37pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/41 "2002-11-06T19:37:26Z")
Never mind. I’ll just tell you why you’re wrong. Silly Putty is a colloidal substance, that , one substance suspended within another. One of those substances is a solid, and the other is a liquid.
As an aggregate though it fails the ASTM test and is therefore a solid.
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### Author:  [@Irishman](https://boards.straightdope.com/u/Irishman)
#### Post date: [November 7, 2002, 6:18am UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/42 "2002-11-07T06:18:21Z")
Apparently in [this](http://boards.straightdope.com/sdmb/showthread.php?threadid=2192) thread, there is a reference to an unfound General Questions thread “where Cecil admits that his earlier column was based on earlier (mis)understanding about the nature of glass.” (This was a UBB thread that my search did not turn up.) This tells me we are due for a correction in Cecil’s column.
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### Author:  [@t-keela](https://boards.straightdope.com/u/t-keela)
#### Post date: [November 7, 2002, 6:34am UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/43 "2002-11-07T06:34:02Z")
I’ve worked in a glass factory. I’ve seen and worked w/ glass in several forms, from a gas to a solid, at least in the common understanding of these terms.
If glass as we (the public) use it in our normal lives is a liquid, then when is it a solid according to this standard?
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### Author:  [@GSV\_Consolation\_of\_Dreams](https://boards.straightdope.com/u/GSV_Consolation_of_Dreams)
#### Post date: [November 7, 2002, 8:12am UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/44 "2002-11-07T08:12:32Z")
Silly putty is pretty strange, it has different physical properties depending on how one interacts with it physically. If you hit it sharply with a hammer it can shatter, but slowly squeeze it and it deforms, drop it on a hard surface and it bounces.
I saw a video clip once wherein some guys with too much time on their hands ordered 50 lbs of the stuff, made it into a big ball and dropped it from a 4th floor balcony. It bouced _and_ shattered.
It is a [dilatant compund](http://www.sillyputty.com/silly_science/silly_science.htm)
Citing from [sillyputty.com](http://sillyputty.com), deary deary me.
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### Author:  [@metroshane](https://boards.straightdope.com/u/metroshane)
#### Post date: [November 7, 2002, 3:47pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/45 "2002-11-07T15:47:18Z")
BTW,
I now side with David. Not necessarily because he’s probably right, but because when I say amorphous solid…most people can’t argue because they have to go look up what “amorphous” means. This is much more satisfying…and yes I was probably being counterintuitive when I won my bet.
I do regret the fact that Cecil is still printing this column with the editorial changes but lacking the recent updates.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [November 7, 2002, 6:32pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/46 "2002-11-07T18:32:18Z")
To put it another way: If glass is a liquid, then rubber is a conductor. Sure, the conductivity of rubber is really low, but it’s not zero.
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### Author:  [@cdhostage](https://boards.straightdope.com/u/cdhostage)
#### Post date: [November 7, 2002, 10:05pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/47 "2002-11-07T22:05:27Z")
I believe that any non-crystalline substance will deform over time if given a constant pull (by gravity for instance).
Without intimate chemical connections to their neghbors, atoms move by eachother. The co-operation of a constant downward force (gravity) and some random motion (heat jiggling - Brownian motion), means that atoms are more likely to end down than up. Like how an uneven field is “falttened” by a snowfall - individual snowflakes (and clumps of them) tend to fall down as far as they can.
Thus, if you put a piece of granite the same dimensions as a piece of glass on a table and left it for a million years, it would have deformned as well. Perhaps more or perhaps less than glass - I don’t know. But as it has no large-scale crystalline structure, it will deform.
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### Author:  [@Irishman](https://boards.straightdope.com/u/Irishman)
#### Post date: [November 8, 2002, 9:19am UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/48 "2002-11-08T09:19:50Z")
**t-keela** , under that definition, I believe the answer is “never”. Glass does not attain a crystalline structure, which is the conventional definition of solid according to the phase-state diagrams.
**atarian** , that is unhelpful, as I have no idea what _dilatant_ means, and can’t find it in my dictionary.
**Scylla** , is this perhaps the reference you found? [http://www.ualberta.ca/~bderksen/florin.html](http://www.ualberta.ca/~bderksen/florin.html)
I also found
[http://www.urbanlegends.com/science/glass.flow/amorphous\_solid\_more.html](http://www.urbanlegends.com/science/glass.flow/amorphous_solid_more.html) and associated pages
[http://www.urbanlegends.com/science/glass.flow/](http://www.urbanlegends.com/science/glass.flow/)
Read This Site!
[http://math.ucr.edu/home/baez/physics/General/Glass/glass.html](http://math.ucr.edu/home/baez/physics/General/Glass/glass.html)
Excellent description, including diagrams of crystal and amorphous structures, and mention of Roman glassware that hasn’t deformed in 2000 years.
The bottom line: Cecil admitted in a previous thread that glass is a solid. The column in question was run on the web site as a _classic_ column, which is why it wasn’t updated. The possibility of an update by Cecil is up to him. If and when he gets to it, then the website will be updated. I have no insight into how the classic columns are chosen for the web site, but I do not expect it is a manual selection process, where someone would have seen the topic and then realized there would be trouble. Perhaps the moderators could poke Ed for us? 😉
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### Author:  [@GSV\_Consolation\_of\_Dreams](https://boards.straightdope.com/u/GSV_Consolation_of_Dreams)
#### Post date: [November 8, 2002, 10:40am UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/49 "2002-11-08T10:40:51Z")
> [@](#):
>
> \*Originally posted by Irishman \*
> **atarian** , that is unhelpful, as I have no idea what _dilatant_ means, and can’t find it in my dictionary.
[Merriam Webster online’s definition](http://www.m-w.com/cgi-bin/dictionary?dilatant)
[Google: “DILATANT”](http://www.google.co.uk/search?q=DILATANT&ie=UTF-8&oe=UTF-8&hl=en&btnG=Google+Search&meta=)
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### Author:  [@roryaxis](https://boards.straightdope.com/u/roryaxis)
#### Post date: [November 9, 2002, 2:45pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/50 "2002-11-09T14:45:11Z")
Okay, what about plexiglass, clear plastic and other things. They are solid, not super-cooled liquids, or liquid like solids, or solid like liquids. And they’re made of polymers, huge molecules. Now, I understand being able to see through silicon or through a cystaline structure, but through long polymers? Doesn’t make sense.
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### Author:  [@Chava](https://boards.straightdope.com/u/Chava)
#### Post date: [November 11, 2002, 4:17pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/51 "2002-11-11T16:17:22Z")
In the common parlance (the one in which a tomato is a vegetable) glass is a solid. It’s incompressible and it doesn’t flow.
In technospeak (tomato is a fruit), glass is neither solid nor liquid. It is a **glass**. A glass does not exhibit crystaline structure and has a glass transition rather than a solid/liquid melting transition. Plexiglass, clear plastic, and other things are also **glasses**. Being a glass does not have anything to do with whether the material is transparent at optical frequencies. Naphthalene, the subject of my high school chemistry glass transition experiment, is opaque white. It also smells like mothballs.
Chava
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### Author:  [@Waverly](https://boards.straightdope.com/u/Waverly)
#### Post date: [November 11, 2002, 5:39pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/52 "2002-11-11T17:39:25Z")
Glass is solid. And I’m talking technically speaking here, not just some subjective, “it feels hard when I hit my head against it.” I can’t believe how often this comes up, and I can see from the links (thanks, by the way) I’ve chimed in on this before.
Glass has a transition temperature (Tg) where it undergoes it’s phase change. Use a TMA, a dilatometer, a DSC, whatever, but if this isn’t a change in state, please explain what it is.
What is more, many crystals we can all agree are solid have a Tg as well. Alumina (Al2O3) and Silica (SiO2), for example. Same chemical formula, same temperature, same _state_, but if you have cooled it too quickly for the crystal structure to form, you have a glass. Conversely, you can take compounds that normally form glasses and cool them in such a way that they are able to form a crystalline lattice. Such ceramed glassed include Pyrex.
Not every solid need have a crystalline structure. I challenge anyone to provide me a cite from an _original_ source that proves otherwise. I have the ASTM vol. 4, the Fundamentals of Inorganic Glasses, and few other texts in my bookcase now, so see if you can find something more compelling.
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### Author:  [@Waverly](https://boards.straightdope.com/u/Waverly)
#### Post date: [November 11, 2002, 7:33pm UTC](https://boards.straightdope.com/t/glass-liquid-or-solid/135210/53 "2002-11-11T19:33:55Z")
I asked for cites, so I should have given some myself:
> [@](#):
>
> 1. A glass is an amorphous solid which exhibits a glass transition
> 2. A solid is a material whose shear viscosity exceeds 1014.6 poise
>
> - _Elliot, S.R. 1983. Physics of Amorphous Materials_
> [@](#):
>
> A glass is “a solid with liquid like structure, a noncrystalline solid, an amorphous solid.” – _Varshenya, A.K. 1994. Fundamentals of Inorganic Glasses_
Several other posters have gone over the ASTM, so I won’t repeat those cites.
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