# glass is liquid, david is wrong **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [October 18, 1999, 3:58pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257 "1999-10-18T15:58:00Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 22, 1999, 12:06pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/21 "1999-10-22T12:06:00Z")
Keith, actually what you said about it just becoming less and less viscous isn’t completely true. There is a glass transition temperature that can be seen on a chart of temperature vs. expansion (heating a solid sample). Materials scientists recognize the difference by calling the material a supercooled liquid until it hits that point (cooling down) and a glass thereafter. ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [October 23, 1999, 2:54am UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/22 "1999-10-23T02:54:00Z")
Just for fun, and by way of making no known rational contribution to this thread – the ‘Statics and Strengths of Materials’ boys always assured us that, in pure compression, glass has roughly the same strength as concrete. Let’s see your liquid silica follow that act! ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [October 23, 1999, 11:10am UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/23 "1999-10-23T11:10:00Z")
\<\< …glass has roughly the same strength as concrete.\>\> You’re taking that for granite. ---
**Author:** ![Webfoot](https://avatars.discourse-cdn.com/v4/letter/w/76d3ee/32.png) [@Webfoot](https://boards.straightdope.com/u/Webfoot)\ **Post date:** [October 24, 1999, 4:45pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/24 "1999-10-24T16:45:00Z")
## So much for glass - what about opal, though? Just because you’re paranoid, don’t mean they ain’t out to get you ---
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 24, 1999, 7:47pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/25 "1999-10-24T19:47:00Z")
Er, what about it? ---
**Author:** ![Webfoot](https://avatars.discourse-cdn.com/v4/letter/w/76d3ee/32.png) [@Webfoot](https://boards.straightdope.com/u/Webfoot)\ **Post date:** [October 24, 1999, 11:14pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/26 "1999-10-24T23:14:00Z")
I’m no chemist - until I read the above, I thought glass was a liquid, and also opal, because opal, like glass, is an unorthodox compound of silica. So if glass is after all not a liquid, is opal also not? That’s what about it. * * * Just because you’re paranoid, don’t mean they ain’t out to get you ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [October 25, 1999, 3:54am UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/27 "1999-10-25T03:54:00Z")
[http://www.public.iastate.edu/~physics/sci.physics/faq/glass.html](http://www.public.iastate.edu/~physics/sci.physics/faq/glass.html) That’s from the sci.physics FAQ. Seems you can’t really say that glass is a liquid OR a solid. * * * Quick-N-Dirty Aviation: Trading altitude for airspeed since 1992. ---
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 25, 1999, 12:16pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/28 "1999-10-25T12:16:00Z")
Tracer, from that FAQ: “In this state it is often called an amorphous solid or glass.” And from the conclusion: “from a more common sense point of view, glass should be considered a solid since it is rigid according to every day experience.” ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [October 26, 1999, 5:58am UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/29 "1999-10-26T05:58:00Z")
And also from the FAQ’s conclusion: “There is no clear answer to the question ‘Is glass solid or liquid?.’ In terms of molecular dynamics and thermodynamics it is possible to justify various different views that it is a highly viscous liquid, an amorphous solid or simply that glass is another state of matter which is neither liquid or solid. The difference is semantic. In terms of its material properties we can do little better. There is no clear definition of the distinction between solids and highly viscous liquids.” ---
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 25, 1999, 6:11pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/30 "1999-10-25T18:11:00Z")
Which I don’t understand how they can say, since they already demonstrated the glass transition temperature. On cooling down after melting, the material does go through a “supercooled liquid” phase – before the glass transition temperature. Then its properties do change somewhat and it becomes a glass. In short, I think they were kind of hedging their bets (or weaseling) when they said there is no clear answer. When I was still in the field, I knew of nobody who considered glass anything other than an amorphous solid. Whether you equate “amorphous solid” with “another state of matter” is, to me, a matter of semantics. It’s a solid, though obviously not a crystalline one. ---
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 25, 1999, 6:15pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/31 "1999-10-25T18:15:00Z")
back and rereading the conclusion, I see that the parts you quoted come before the parts I quoted – the parts I mentioned were kind of the overall summary to the question he raised (and you quoted). He also noted: > [@](#): > > The use of the term “supercooled liquid” to describe glass still persists but is considered by many to be an unfortunate misnomer which should be avoided. So let’s avoid it. 🙂 ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [October 26, 1999, 4:06pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/32 "1999-10-26T16:06:00Z")
Glass is a solid. It may however, be useful for me to explain what happens to a glass as it is cooled, and the various changes it makes. There are more than one. At first, the glass is a free flowing liquid. The individual movements of each of the molecules are relatively independent of one another. As the glass cools, it begins to go through, a state where, if one molecule moves, the others around it have to move. Even water exhibits this state below 4 deg C. This is considered to be a glassy state. Honey is usually in this state at room temperature. What happens next strongly depends on how fast the cooling process is occuring. If the cooling process is slow, a certain amount of crystaline order can be obtained. Notice what happens to honey on cold days. It crystalizes. If you put your honey in the refrigorator, however, it will cool too fast to crystalize. This is because the honey as cooled too fast to develop the thermodynamically preferd order of the crystal. Once the molecules of the glass have been fixed in place, they do not flow. This is what occures at the glass transition temperature. Notice that the glass transition temperature will strongly depend on the cooling rate. It is not a well defined for a particular molecule. Interestingly, some molecules prefer to develope crystal;ine order even before they become solids. Thus we call them liquid crystals. But that is another subject all together. * * * All truly original art is ugly at first. ---
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 26, 1999, 4:34pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/33 "1999-10-26T16:34:00Z")
Christopher said: > [@](#): > > As the glass cools, it begins to go through, a state where, if one molecule moves, the others around it have to move. … This is considered to be a glassy state. Um, no, it’s not. It’s a supercooled liquid. It’s not in a glassy state until it passes the glass transition temperature. But otherwise you were pretty much on target. ---
**Author:** ![KeithB](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@KeithB](https://boards.straightdope.com/u/KeithB)\ **Post date:** [October 27, 1999, 10:20pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/34 "1999-10-27T22:20:00Z")
Not that it matters, but the epoxies used to encapsulate the plastic chips must also be amorphous solids. The temperature of the chip must be kept below the “Glass Transistion Temperature.” I never made the connection, duh! ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [October 27, 1999, 11:22pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/35 "1999-10-27T23:22:00Z")
A supercooled liquid only exists below Tf. As we all know Tf for water is 0 deg C, and not 4 deg C. However, water has it’s maximum density at 4 deg C. This is because the intermolecular forces are begining to take over. This state is sometimes refered to as a glassy state. It is still very much a liquid, and not a supercooled liquid. ---
**Author:** ![David\_B](https://avatars.discourse-cdn.com/v4/letter/d/51bf81/32.png) [@David\_B](https://boards.straightdope.com/u/David_B)\ **Post date:** [October 28, 1999, 1:27pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/36 "1999-10-28T13:27:00Z")
Keith: There are many similarities between polymers and glasses. In fact, some would say that glasses are a type of polymer. Christopher: I don’t know who these people are that talk about water in the glassy state, so I can’t comment on them. All I can say is that it directly contradicts what is in all the glass and materials science textbooks and journal articles I have ever seen. It may be a case of the same term being used in a different area to mean a different thing. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [October 28, 1999, 4:49pm UTC](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257/37 "1999-10-28T16:49:00Z")
## David B: It doesn’t contradict anything at all. Everything you have said is absolutely correct. It is true that glassy water is not a particularly usefull term to anyone other than a physical chemist. It certainly would not appear in any materials journal. It may even be a bit out dated. I cant remember the last time I had seen it used. It is however an actual phenomenon. In addition to a minimum volume, the viscosity of water significantly increases at 4 deg C. I apologies for not being clear on the distinction between Tf and the glassy state of a liquid. I find the analogy usefull in a discussion concerning glasses, because it helps me visuallize the interdependence of molecular motion, in a liquid state. One can imagine that the molecules of water are moving in and out of crystaline and non crystaline domains. This is essentilly what happens when a glass freezes itself into these domains. All truly original art is ugly at first. [Previous page](https://boards.straightdope.com/t/glass-is-liquid-david-is-wrong/1257.md?page=1)