# Glass as a Liquid? **URL:** \ **Category:** Factual Questions\ **Created:** [August 29, 2013, 1:40am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463 "2013-08-29T01:40:41Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 29, 2013, 1:40am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/1 "2013-08-29T01:40:41Z")
While I know the chemists will define glass as a liquid since it lacks a crystalline structure, i.e., a latticework at the atomic level. Furthermore, my chemistry teacher (from yesteryear) would claim windows will run out of their sills in maybe a 100 years. She claims they found windows in old churches that are thicker at the bottom than the top which supports this argument - that glass is a liquid of high viscosity. What’s the whole story on this? Can we witness “running windows” in our lifetime? Where can I find real-world examples in real-time…all around us? (I don’t think I can wait 100 yrs nor take the kids to some old European church!) ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [August 29, 2013, 1:46am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/2 "2013-08-29T01:46:26Z")
No, the whole window glass flowing downwards is a myth. Glass panes when made back in the day were imperfect pours and ended up being uneven thickness. Workers purposely installed them with the thickest side on the bottom for a uniform look. ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [August 29, 2013, 1:46am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/3 "2013-08-29T01:46:44Z")
Chemists do NOT define glass as a liquid, and [it does NOT flow at all](http://www.glassnotes.com/WindowPanes.html). ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [August 29, 2013, 1:51am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/4 "2013-08-29T01:51:31Z")
Glass is an amorphous solid, not a liquid. The glass was installed in those church windows thick edge down and didn’t flow. This subject has been done before. [http://boards.straightdope.com/sdmb/showthread.php?t=645199&highlight=glass+flow](http://boards.straightdope.com/sdmb/showthread.php?t=645199&highlight=glass+flow) ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [August 29, 2013, 1:51am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/5 "2013-08-29T01:51:45Z")
I could’ve sworn there was a SD column on this but I can’t find it. Anyway, [the section on Wikipedia](http://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass). Summary: She was operating under an urban legend. Old glass windows are thicker on the bottom solely because of how they were made. Cooling glass spun like a centrifuge and cut to shape. The thicker part was on the bottom because it’s more structurally sound. See also the info on “amorphous solid.” 100 years is an extremely “optimistic” number for other times I’ve heard this UL. ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [August 29, 2013, 1:53am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/6 "2013-08-29T01:53:27Z")
The next time someone tells you this story, ask them why there aren’t any puddles of glass around the windows of the older churches in Europe. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 29, 2013, 2:07am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/7 "2013-08-29T02:07:21Z")
> [@Inner\_Stickler](#): > > The next time someone tells you this story, ask them why there aren’t any puddles of glass around the windows of the older churches in Europe. That’s simple. They turn the churches upside down for a few years every century to arrest the flow. Duh. Stranger ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [August 29, 2013, 2:09am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/8 "2013-08-29T02:09:20Z")
:headsmack: ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [August 29, 2013, 2:20am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/9 "2013-08-29T02:20:37Z")
> [@thelurkinghorror](#): > > I could’ve sworn there was a SD column on this but I can’t find it. Anyway, [the section on Wikipedia](http://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glass). > > Summary: She was operating under an urban legend. Old glass windows are thicker on the bottom solely because of how they were made. Cooling glass spun like a centrifuge and cut to shape. The thicker part was on the bottom because it’s more structurally sound. See also the info on “amorphous solid.” > > 100 years is an extremely “optimistic” number for other times I’ve heard this UL. There is a SD article on it, but it isn’t exactly great on the fighting ignorance front: > [@](#): > > Not to beat around the bush or anything, Dan, but the reason you can see through glass basically is that there is no reason for you not to be able to see through it.\*\* Despite its appearance, glass is really a highly viscous liquid\*\* rather than a solid, and you can see through it for the same reasons that you can see through water. Cecil backtracked half-assedly later on: > [@](#): > > Now, Shayne. The mark of a truly great mind isn’t whether you’re right or wrong. It’s how well you can weasel out of a jam. > > Lesser folk might prefer it otherwise, but there’s no sharp line dividing liquids and solids. A supercooled liquid, the term applied to glass for many years, has been rapidly chilled past its normal freezing point and become apparently solid without assuming the regular crystalline structure typical of solids.\*\* The term du jour, amorphous solid, means an apparently solid substance that lacks crystalline structure and instead has the random organization of liquids. In other words, we used to think of glass as a solidlike liquid, and now we think of it as a liquidlike solid. Big frickin’ deal.\*\* > > I concede that changes in the properties of glass once it cools past the “glass transition temperature” are an argument for calling it a solid.\*\* But to my mind the real question is whether glass flows, as liquids do. I’m happy to say it does, just not very fast\*\*. In the original column I wrote, “At room temperature [glass’s] rate of flow is so slow that it would take billions of years to ooze out of shape.” In the October 1999 issue of Discover, Yvonne Stokes, a mathematician at the University of Adelaide in Australia, says that it would take a mere ten million years for a windowpane to get 5 percent thicker at the bottom. So the way I see it, not only was I essentially right, I was being conservative by a margin of 100 to 1. > **[How come you can see through glass?](https://www.straightdope.com/21341284/how-come-you-can-see-through-glass)** emphasis mine ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 29, 2013, 2:24am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/10 "2013-08-29T02:24:02Z")
> [@california\_jobcase](#): > > Glass is an amorphous solid, not a liquid. The glass was installed in those church windows thick edge down and didn’t flow. This subject has been done before. > [http://boards.straightdope.com/sdmb/showthread.php?t=645199&highlight=glass+flow](http://boards.straightdope.com/sdmb/showthread.php?t=645199&highlight=glass+flow) Nope! Your referenced thread includes a link to a Cecil response where he concludes it is a liquid, and it IS flowing, although very, very, very, very slow: (NOTE: Read in its entirety) …did I say very, very, very slow? > **[How come you can see through glass?](https://www.straightdope.com/21341284/how-come-you-can-see-through-glass)** ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 29, 2013, 2:27am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/11 "2013-08-29T02:27:53Z")
> [@Darth\_Panda](#): > > There is a SD article on it, but it isn’t exactly great on the fighting ignorance front: > > Cecil backtracked half-assedly later on: > > [How come you can see through glass? - The Straight Dope](http://www.straightdope.com/columns/read/110/how-come-you-can-see-through-glass) > > emphasis mine No, he really DID NOT backtrack. At the very, very end, he concludes IT IS FLOWING! Therefore, it IS a liquid. See ya in a million years when my laptop screen puddles all over its keyboard. 😉 ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [August 29, 2013, 2:58am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/12 "2013-08-29T02:58:45Z")
Yeah, guys, I think Jinx just took you to school on what Cecil’s ‘retraction’ said. 😛 ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [August 29, 2013, 6:02am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/13 "2013-08-29T06:02:01Z")
> [@Darth\_Panda](#): > > There is a SD article on it, but it isn’t exactly great on the fighting ignorance front: Wow, that’s a really bad article. I presume Cecil never looked through a quarz crystal? Anyway, regarding the original question in the article, why one can see through glass, **Pasta** does a great job of clearing up the issue [in this post](http://boards.straightdope.com/sdmb/showpost.php?p=16344434&postcount=4), by rebutting the other common misconception, that the light ‘bounces from atom to atom’. ---
**Author:** ![Pjen](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Pjen](https://boards.straightdope.com/u/Pjen)\ **Post date:** [August 29, 2013, 6:07am UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/14 "2013-08-29T06:07:33Z")
A recent science program on UK television discussed the issue (Dara O’Briain’s Science Club). It dismissed the glass flow issue but mentioned in passing the question of whether Pitch was a liquid and referenced the oldest known continuing experiment to test this empirically (about 70 years) rather than rationally. > **[Pitch is a liquid, finally drips after 69 years - UPI.com](https://www.upi.com/Science_News/Blog/2013/07/19/Pitch-is-a-liquid-finally-drips-after-69-years/3791374265046/)** > > A 69-year long experiment finally yields results -- tar pitch is world's slowest-moving liquid. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 29, 2013, 3:09pm UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/15 "2013-08-29T15:09:49Z")
Saying that glass is a liquid is like saying that glass is a conductor. Yes, it has a finite viscosity, just like it has a finite resistivity, but they’re both really, really high, such that it’s almost always fine to approximate them as infinite. ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [August 29, 2013, 3:15pm UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/16 "2013-08-29T15:15:17Z")
The earth’s crust bends and settles, so, it too is a liquid. Large heavy blocks of so-called ‘solid’ metal will deform over time, so, they’re also really a liquid. The real question is “Is solidity an illusion?” ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 29, 2013, 3:40pm UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/17 "2013-08-29T15:40:35Z")
if something is a liquid seems to be a fluid issue. ---
**Author:** ![pravnik](https://avatars.discourse-cdn.com/v4/letter/p/8edcca/32.png) [@pravnik](https://boards.straightdope.com/u/pravnik)\ **Post date:** [August 29, 2013, 4:10pm UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/18 "2013-08-29T16:10:20Z")
Glass is a liquid. Just not at room temperature. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 29, 2013, 4:12pm UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/19 "2013-08-29T16:12:35Z")
> [@moriah](#): > > The earth’s crust bends and settles, so, it too is a liquid. Large heavy blocks of so-called ‘solid’ metal will deform over time, so, they’re also really a liquid. The real question is “Is solidity an illusion?” Neither of these are strictly speaking, true. The technical definition of a liquid is a continuum which has no regular structure, a resistance to shear based slowly on the differential velocity, and is in essentially one state with mechanical properties which are isentropic. Most solids, and especially metallic solids and intermetallic compounds, have both a local and global structure (the local metallic lattice and the larger grain structure), a resistance to shear based upon deflection from the equilibrium state, and are not typically isentropic (although many metals are often treated so for engineering purposes). Deformation of solids is caused by adding energy to the lattice in a manner analogous to compressing a spring, or altering the large scale structure. (Some heat treatment, tempering, diffusion, and other processes can also alter the small scale structure by changing the configuration of the lattice.) Liquids, having no structure, will ‘deform’ (flow) permanently in response to any non-equilibrium loading. Glass is best characterized as an amorphous solid; that is, it has no large scale structure, and only a very irregular short range structure. It is true that glass and glass-like substances will start flowing under sufficient heat or pressure (which are far greater than anything experienced in typical terrestrial conditions), and the lack of well-defined structure means that unlike solids, there is no well defined line at at which a phase transition occurs; hence why you will see engineers arguing over the “glass transition temperature” of a particular substance with a wide range of temperatures depending on the particular set of mechanical characteristics they may be concerned about and/or the conditions and methods by which which it may be experimentally determined. “Solidity” at the macroscopic level is generally well-defined insofar as solid objects will fracture or be permanently deformed when stressed excessively, while liquids will flow and reform to match the shape of any container they are poured into. At the molecular and atomic level, solidity is much more vague, and in fact the boundary between a control volume and the area adjacent to it isn’t even well defined, as individual atoms and molecules may separate and recombine continuously. Stranger ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [August 29, 2013, 4:15pm UTC](https://boards.straightdope.com/t/glass-as-a-liquid/667463/20 "2013-08-29T16:15:26Z")
> [@](#): > > In the October 1999 issue of Discover, Yvonne Stokes, a mathematician at the University of Adelaide in Australia, says that it would take a mere ten million years for a windowpane to get 5 percent thicker at the bottom. So the way I see it, not only was I essentially right, I was being conservative by a margin of 100 to 1. So those churches are older than Humanity? Christian veneer over the top of the Old Ones? 😛