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Picture of lead glass[edit]

Not sure this can be the case. From what I remember, PbO glass has a faint greenish colour. This is more likely sodium borosilicate glass (i.e. pyrex). User:Rvlaw 4 January, 2016

I'm not sure which photo you're referring to. If it's the welding photo, that is definitely common lead-glass used in neon-lighting construction. I have a ton of it at home. It's very clear in thin sections, but in cross-section (when I cut the tube and look down its length, it is very yellow in color (as opposed to the turquois-blue of soda-lime or the white of fused silica). Borosilicates can have a range of colors, from white BK7 to brown Pyrex. Greenish-blue tint is usually from iron. Zaereth (talk) 22:31, 7 January 2016 (UTC)

Behavior of antique glass[edit]

How should this section be reworked since the statement "...once solidified, glass does not flow anymore." is at odds with results found in the paper "Relaxation time and viscosity of fused silica glass at room temperature" by M. Vannonia, A. Sordini, and G. Molesini in the European Journal of Physics E Volume 34, 2011? Dan Watts (talk) 14:48, 12 April 2013 (UTC)

I don't know, so I will have to defer to others, because I do not have access to the full paper. I was able to locate the first two pages, here. From what I have read, there doesn't seem to be any cause attributed to the deformation. What we have here is a detailed analysis of a pair of optical flats that were purchased in 1981, which were rarely used, but were found to be off by a few nanometers in 2008. They equate the deformation to viscous flow, but don't actually say viscous flow is the culprit. In fact, to quote, "Although still on a dubitative ground as to the causes of the observed behaviors, cases of long-term defomation of fused silica plates at room temperature have been reported."
To me, this is an example of why extreme caution should be taken when using primary sources. A good, reliable, secondary source can often provide a much better interpretation. The problems I see with this one (albeit, I haven't read the whole thing ... I think) are: 1) The article reports this as an unexplained deformation. 2) The flats were only tested between 2008 and 2010, during which time there was "no appreciable change." However, during this time, they noticed that there seemed to be a deviation from the original flatness. 3) There is no way to actually know what the true (absolute) flatness originally was, because they were not originally subjected to the three-flat test. They may have been off the whole time, because flatness of the sample flat in an interferometer test is usually relative to the flatness of the test flat 4) This is a very small case study (only two flats, one type of glass, over a two year period, with no change during that time).
I would definitely not try to use this as definitive proof, because it is an admittedly incomplete study. Zaereth (talk) 22:26, 12 April 2013 (UTC)

I appreciate your response, and delving into the references (including one that did observe masurable deviation and is available { } ) it appears that the first paper is not the best one to use. Perhaps you could also look at this one. Dan Watts (talk) 01:42, 14 April 2013 (UTC)
No problem. This report is similar, except the study is more detailed. This is a study of five flats, of which, only two actually showd any deformation. With one flat, the deformation was rather uniform, similar to the other report's. The other flat showed deformation only in the center, as if the properties of the fused silica varied across the flat. The other three flats showed no deformation during the test period. The report also claims the cause as unknown and, what's more, they have no idea why some flats deform while others do not, and still others only partially deform.
I'm beginning to think this info would best be suited to the fused silica article, but definitely not for antique glass. The optical flat article could definitely use more information. While the report equates the deformation in the fused silica to a viscosity of 1017 Pa s, it still lists soda-lime glass as being around 1041 Pa s. Significantly higher.
These studies show that deformation does occur in fused silica in a way that it does not in other glasses. Further more, it also shows that such deformation is not universal, but sporadic, indicating some possible deviation of the material's make-up. When including this info into an article, I would be careful to explain all of this, to state that the deviations are on the order of a few nanometers, and the conclusion is that "no observable effect is ocurring over human lifetime." Zaereth (talk) 17:19, 15 April 2013 (UTC)
Perhaps the conclusion should be "no unaided observable effect is ocurring over human lifetime." They did measure an effect for two flats. Dan Watts (talk) 18:43, 15 April 2013 (UTC)
I can agree with that, and almost added a similar adjectives to the quote, but I would've had to put it in brackets to avoid misquoting. Zaereth (talk) 18:56, 15 April 2013 (UTC)


Could we get more-definitive dates in antiquity? and a clearer outline, chronologically, in the History section? Thanks! Now to look for more info about window glass. Misty MH (talk) 08:39, 25 July 2013 (UTC)

English spellings[edit]

It appears this article was started using American English in 2001, and then was switched by an IP user in 2006 to British English, for no apparent reason. I will be switching it back as time allows. — Preceding unsigned comment added by (talk) 15:46, 22 August 2014 (UTC)

I've reverted you - we have to keep spelling in references; and if correcting, change spelling all through the article. I'll try to correct this today. Materialscientist (talk) 21:52, 22 August 2014 (UTC)

--Sorry, I attemped to keep them all straight in the refs, must have missed one. Obviously didn't try to convert the it'll lead to dead links

  • I was wondering about this. The article should be consistent in its spelling and at the moment it is not. Do any other editors remember a discussion about changing to British English? It appears true that the article was started in American English and was changed in 2006. It has therefore been (predominantly) in this dialect through a longer time and many more edits. Does anyone feel strongly about which way the article should standardise? --John (talk) 23:22, 22 February 2015 (UTC)
Personally, I don't feel strongly one way or the other. I noticed you had changed a couple of words to British spellings, but did not go through the entire article and change them all, so I felt it needed better consistency. I checked the original version of the article, and then checked the entire article as it now exists (using ctrl+F), and it both started and is currently, primarily written in American English. (See the section on color, for example.) Spellings should not be changed within the references, but the text should remain consistent. Zaereth (talk) 23:32, 22 February 2015 (UTC)


The lead of this article doesn't appear to me to be very clearly worded. Is it defining glass as the familiar substance found in windows etc., or all substances capable of a glass transition? The first few sentences seem to define glass in a broad sense, then later it states "In science, the term glass is defined in a broader sense, encompassing every solid that possesses a non-crystalline (i.e. amorphous) structure and exhibits a glass transition when heated towards the liquid state" - yet this is what was stated at the beginning, is it not? It also refers to "silicate glass" without explaining what that is - is it the same as the previously mentioned soda-lime glass? PaleCloudedWhite (talk) 08:54, 4 November 2014 (UTC)

The answer is both. In a general sense, as understood by most people, "glass" refers to silicate glass, which is glass that is made primarily from silica. This can be either pure, fused-silica, or it may have other additives like lime, boron, lead, or iron to change its color and melting temperature. Silicate glasses are what most people think of when they hear the term "glass." This definition is more general, but also more specific, because it is referring to a very specific type of material.
In the scientific sense, the meaning is more specialized, yet has a broader coverage of materials. This includes things like porcelain and plastic, which a general audience usually doesn't think of as being glass. However, when, say... welding glass, it behaves very similar to welding plastic.
The purpose of the lede is to have a very general summary of the entire article. The first sentence should define the term in its broadest sense, and then more general and specialized definitions should follow. I do think you're right, that silicate glass should be defined, and perhaps the wording could be clearer, but the term glass is used to cover all these definitions, so that needs to be covered in the lede. I'll look into this further when I get more time. Zaereth (talk) 17:22, 4 November 2014 (UTC)
Thanks for replying. I would have been bold and made some adjustments myself, were it not for my lack of knowledge. I imagine the defining of silicate glass could be done fairly simply. The other matter - of wording - perhaps requires more input. I'm trying to understand the difference between the broad yet specialised scientific definition and the definition "in its broadest sense", because at the moment the lead seems to imply they are the same. Would it be technically correct to state, as the first sentence, "Glass is any amorphous solid (non-crystalline) material that exhibits a glass transition", rather than "Glass is an amorphous solid (non-crystalline) material that exhibits a glass transition"? PaleCloudedWhite (talk) 21:15, 4 November 2014 (UTC)
Thank you. It's a lot easier to spot problems after someone points them out, so your comments are very helpful.
That seems like an OK solution for the time being. You may also want to fix the last sentence of that paragraph, changing "this" into "silicate glass" (in quotes) and then add a brief definition of the jargon.
I see many other problems, especially with that first sentence, which I find to be an extremely circular definition. It's like saying, "Metal is a metallic substance that displays the qualities and properties of a metal." We can't define glass a simply being amorphous and having a glass transition, without confusing the hell out of any newcomers to the field and its jargon. Unfortunately, I am at work, and only have time when I am on hold or whatever, so it may have to wait a while for me to give this the attention it needs. In the meantime, you are more than welcome to make the change you suggested, or anything else that helps improve the article. Zaereth (talk) 21:37, 4 November 2014 (UTC)
Thanks. I've changed the first sentence as proposed. I'm still not sure if "silicate glass" is the same as "soda-lime glass", so haven't altered anything else as yet. This is a new topic for me. I agree the first sentence is generally confusing - I wonder if it's possible to write a definition which doesn't necessitate readers having to follow links before they understand what's being said? I shall also give this more thought, albeit tomorrow - because while it's worktime in Alaska, it's bedtime here in London... PaleCloudedWhite (talk) 22:14, 4 November 2014 (UTC)
Yes, soda-lime glass is a form of silicate glass, and is most commonly used for windows. It also includes lead glass, borosilicate glass, quartz glass (fused silica), pyrex, etc... It also includes various stained glasses, which have metal additives to color the glass. Neodymium colors it purple (and is also good for laser material), chromium colors it green, and uranium pink. A typical, green beer or wine bottle is likely colored with iron. All of these glasses have silica as the prime ingredient. Zaereth (talk) 00:17, 5 November 2014 (UTC)
Okay, present lede is now in nested form suggested above. Let me know if it's still confusing. SBHarris 00:56, 5 November 2014 (UTC)
Hi Sbharris. It does look a lot better to me. (I meant no offense it you are the author of the sentence.) The thing I always try to consider is that the first sentence will be read by everybody, and that includes small school-children. In fact, the average elementary-school child will probably only read the first sentence and never go any farther. Very rarely will they venture past the lede, so I try to keep that in mind when wordsmithing that first sentence.
I try to think of it like this: The first sentence should define the entire subject in the fewest, simplest words possible. So the question to answer is, what is a glass and how is that different in comparison to other materials. (Sorry, just thinking outloud here.) So what are the properties of a glass? How about: "Glass is a solid material that has no specific melting temperature and no microscopic crystals that make up its structure. This lack of crystal structure is referred to as "amorphous" (non-crystalline). A glass is a material that exhibits a glass transition, which is the reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle state into a molten or plastic state...." Or something like that. How does that sound?
Also, I would drop the phrase "as noted above" because it not only is unnecessary, but it also turns the writing into second-person. Zaereth (talk) 02:21, 5 November 2014 (UTC)
Saying in the lead that a glass doesn't have a melting point is opening up a can of worms and I've removed it. I think the first sentence that states a glass is an amorphous (non-crystalline) solid that exhibits a glass transition is a good enough summary, I don't feel it is necessary to describe the detailed characteristics of the glass transition in the lead, since we wikilink to its specific article. Polyamorph (talk) 10:57, 5 November 2014 (UTC)
Possibly, instead of trying to describe the glass transition, we could just add a sentence following the first sentence e.g. "glasses are typically formed by supercooling the melt, forming a supercooled liquid which solidifies at the glass transition." That provides a wikilink to the reader to supercooling and supercooled liquid and is less confusing to the general reader, possibly! Polyamorph (talk) 11:05, 5 November 2014 (UTC)
Done. Polyamorph (talk) 11:16, 5 November 2014 (UTC)
Hi Polyamorph. Long time no see. Well, I guess I'm just old-school, because I've been doing this long before wikilinks or even the internet was invented. My personal view is that the lede should never need a wikilink for people to understand what it's talking about. Imagine coming to this article for the sole purpose of finding out what the heck this term "glass' means, and having to read three other articles just to understand what the very first sentence means. That's pretty discouraging and is more likely to deter people from reading any further.
When writing the first sentence, I always try to think of it like this: How can I define the entire subject in a single sentence, with as few words as possible, and have it be able to stand on its own without any help from other articles. Imagine you need to define "glass' for a class of elementary-school children, and one sentence is all you get. No wikilinks. No other information to help you, but all you have is one sentence to give these kids the best understanding of the subject that you can muster. As I see it, that is the challenge. Zaereth (talk) 18:12, 5 November 2014 (UTC)
I get your point, but the lead is supposed to summarise what is in the article. So a full explanation in the lead is not necessary, just a summary of the key concepts as all can be explained in more detail in the article. Since this article deals with glass in the general sense, and not just the state of matter, i dont feel we should over emphasise the physics in the lead. I felt that as it stood the summary was overly confusing. but that's my opinion. I also removed some repetition. Polyamorph (talk) 22:56, 5 November 2014 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── I don't think it's very helpful to say that a glass is something that undergoes a "glass transition" and leave that as a link with no explanation. That's like saying that morphine induces sleep by means of its dormative or narcotic properties. Or that an anesthetic is anything that produces a state of anesthesia. And talk about opening up a can of worms-- why introduce the concept of "supercooling," and "quenching" especially when you don't need it? Glasses are traditionally formed by rapid quenching and undercooling of a liquid, forming a supercooled liquid which solidifies at its glass transition temperature This isn't even TRUE. Window and bottle glass don't need rapid quenching, and any rapidity in the process is only to increase throughput in manufacture. Typically, silicate glasses can be vitrified and devitrified at will without fear of crystalization, and with any speed you like (if you've watched a glassblower work). So the sentence above makes an explanation and leaves an impression that is simply false for the most common type of glass the reader will have any experience with! SBHarris 23:40, 5 November 2014 (UTC)

I didn't say it was perfect. Supercooling is certainly needed, I agree with you about the rapid quenching part though so have removed that. As Zaereth said, we need a simple introduction of what a glass actually is. I believe what we had before was confusing. It may well still be confusing. But lets fix that. I also don't understand the adversity to wikilinks. We can't go defining every single term whenever it arises. Wikilinks are part of the beauty of wikipedia. But Zaereth is right. The question is how do we go about it? Polyamorph (talk) 10:03, 6 November 2014 (UTC)
The first sentence currently reads "Glass is any amorphous (non-crystalline) solid material that is capable of going from a hard to a more fluid state with increased temperature, without changing phase". This is still misleading, because as a glass is heated through Tg it undergoes a continuous phase change to a supercooled liquid. So as it stands, the lead is inaccurate. I'm not sure this is the best way to define, to a lay reader, what glass really is.Polyamorph (talk) 12:05, 6 November 2014 (UTC)
Personally, I think we need a much more general definition as the first sentence, keeping "Glass is an amorphous (non-crystalline) solid" but continuing with something along the lines of how it has widespread practical, technological and decorative usages. Then leave any of the science discussion regarding Tg, its formation and viscous behaviour to the final "science" paragraph of the lead.Polyamorph (talk) 12:16, 6 November 2014 (UTC)
Thanks everybody. Sorry I didn't respond sooner, but I've been terribly sick for the last week. (Still not over it.) I think that opening sentence does look a lot better as a nice, simple introduction to the subject, and the lede overall has better flow and cohesion. Thanks for your assistance with this, everyone. It's really nice to participate in some good collaboration like this. Zaereth (talk) 18:09, 10 November 2014 (UTC)

Lead revisited[edit]

I'm going to start this topic again. The definition of glass in the first lead paragraph is still unclear and circular. Definitions must be invertible. If you say, glass is such-and-such with the properties of so-and-so then everything that is such-and-such with properties of so-and-so must be glass without exceptions.

It is perfectly OK if your definition has a little wiggle room but only if the term itself applies to different referents. But if you give two definitions of glass, let's say "glass in common usage" and "scientific glass" and I give you any object, you must be able to say, according to the two definitions, that (1) the object is or is not "common glass" and that (2) the object is or is not "scientific glass". For example, does quartz meet the definition of glass? Does flint?

The 1913 Webster defines glass as "A hard, brittle, translucent, and commonly transparent substance, white or colored, having a conchoidal fracture, and made by fusing together sand or silica with lime, potash, soda, or lead oxide." Obviously, this must be brought up to date but are the words brittle, translucent, conchoidal fracture and fused sand or silica plus amorphous solid enough to make up the definition of glass? --RoyGoldsmith (talk) 19:13, 30 September 2015 (UTC)

Here's the thing. The 1913 definition is adequate for silicate glass. However, due to scientific advancements, the term in a scientific context now refers to much more than silicate glass. In fact, although some materials form a glass more readily, just about anything can become a glass if it is cooled sufficiently fast and low enough to produce a glass transition without crystallizing first. Water can become a glass. (If you're ever cryogenically frozen, you'll want to do it fast, so that all that water in your body doesn't crystallize and rupture the cells.) So can sugar. (Many hard candies like peanut brittle, suckers or Jolly Ranchers are in fact glasses.) Metals can become glass, but the cooling rate needs to be extremely fast. Quartz only becomes a glass if the cooling rate is quick enough, or else you end up with crystal quartz, which is not as transparent. (Fortunately, in quartz and other glass formers, this rate is quite long.) Flint? Probably, if the same conditions are met. Now, the language has changed, as languages often do, but the general population has not yet caught up to the science, so we have these two seemingly-conflicting definitions to deal with. The challenge is to bring both of these definitions together and show that one is merely an extension of the other, and not really different at all, but that is nearly impossible to do in a single sentence, or even a single paragraph. Therefore, in my opinion, it is best to start with the general definition, and then explain how that relates to the scientific one, similar to the way SBHarris has already laid it out. Zaereth (talk) 20:31, 30 September 2015 (UTC)
I think the current definition is fine. Glass is an object in everyday use and in general that glass is silica based. However, scientifically we have many forms of amorphous materials which may be classified as glass. We described both definitions and I don't see any issue. Polyamorph (talk) 09:02, 1 October 2015 (UTC)
You know, on a side note, I find this a lot in many articles where the language changes in one context yet not in another, which leaves us the task of sorting out the confusion without attempting to change the language. For example, certain people constantly want to change the alloy wheel article to include steel wheels, or who come to the alloy steel article complaining that steel is also an alloy. A hundred years ago, steel wasn't considered an alloy, because at the time "alloy" referred to a mixture of metals. It is fairly recent that "alloy" came to include metals mixed with non-metals, yet the language is still full of these conflicting terms to sort out. (Be glad you're not working on a dictionary.) Zaereth (talk) 18:02, 1 October 2015 (UTC)
Polyamorph, you may be right. Can you think of a common "amorphous (non-crystalline) solid" (the current definition in the article) which is not glass? Can we say that translucency (not necessarily transparency) is a necessary condition for glass, including 99% of modern glass? This is not a high-school geometry class -- one case in some obscure field of technology does not invalidate a definition. After all, the developers of that so-called "glass" may by wrong in using the term glass. Does glass need to be brittle, using the 99% rule? Does it need to be solid?
Toffee? Translucency to what wavelength? Black glass is a thing we recognise as glass. Opal glass also. Should we exclude obsidian? Plantsurfer 18:22, 2 October 2015 (UTC)
@Zaereth: you talked about a "glass transition without crystallizing first". The lead paragraph in the article Glass transition contains the statement: An amorphous solid that exhibits a glass transition is called a glass. Couldn't this be used in our article:
Glass is an amorphous solid that has undergone a glass transition; that is, has exhibited the transition from molten or rubber-like liquid to a hard and relatively brittle solid without crystalizing. Glass is often transparent and has widespread practical, technological, and decorative usage in things like window panes, tableware, and optoelectronics. ...
Can you think of a glass that has not undergone a glass transition? To reverse, can you think of any solid which has undergone a glass transition but which you would not classify as glass? --RoyGoldsmith (talk) 17:56, 2 October 2015 (UTC)
Glass is not rubber-like in any respect Michelin would recognise. When molten it is more like molasses, or toffee. It does not stretch and rebound.It does not compress and rebound. We probably won't be seeing glass bands or tyres any time soon. Plantsurfer 18:22, 2 October 2015 (UTC)
See, this is the type of confusion that needs to be sorted out. I would estimate a good 90% of people coming here (and I'm being conservative) are simply looking for the definition of the glass that we scientifically term "silicate glass." Most of the people who come to an article aren't going to read the whole thing, they just want the question "What is glass" answered in as few words as possible. Those who come for the broader definition are much fewer and likely will read the entire lede at the very least.
Transparent glass is what we are most familiar with, but, scientifically, glass does not necessarily need to be transparent or translucent at all. Porcelain certainly is not, and that is for just about all wavelengths. (Quartz is only transmissive from ~ 170 nm to 3000 nm. Other silicate glasses are even less.) Metallic glasses are not. They do not necessarily need to be brittle. Teflon is not brittle at all. They may in fact be rubbery when molten, like PVC, but this is not a necessity. I'd defer to Polyamorph on this as the local expert, but the two condition that must be met is that they are amorphous and that they exist below their glass transition. Toffy, honey, or corn syrup are not glasses at room temperature; they are glass formers. Drop the temperature enough they become glass. (For honey that's around -60 degrees F.) Zaereth (talk) 18:55, 2 October 2015 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── BINGO, Zaereth. The problem isn't really with the lede at all, but the fact that it's being tasked with summarizing an overlarge article. Our underlying problem is with the dab, the directs, and the fact that we now have a bloated article ready for mitosis. What we really need, is an article split:

[1] One article called Silicate glass (not a redlink now, because it redirects to glass, instead of a redirect that should be the other way around!),

[2] Another called Glass types and uses (which would have a small section on silicate glass, with this as as a main article, but focus mostly on all the other types of glass)

[3] And finally one called Glass (physical state), which discusses the physics of glass as a state of matter.

Just about everything in this monster article can be divvied up into these three, with a few synopses per WP:SS for things in one article that need to be summarized in one or both of the other two. The subarticles in this article can be similarly divvied up. Finally, when somebody enters "glass" in the search box, it can redirect to Silicate glass with a note to look at the other two articles for other types of glass and for information about the glass physical state. SBHarris 22:33, 2 October 2015 (UTC)

I agree with that. Looks like a gargantuan task, though. I can help, but may not have much time until winter fully sets in. (Then I'll have lots of time.) The thing I would want to avoid is circular reasoning, which (no offense to anybody in particular and certainly not on this article) is all too common in both scientific and technical media, of all kinds. You ask, what is energy? "Well it's mass." What is mass? "Well it's energy, dont'cha know? Mass and energy are equal." Try to find out what wattage is. "Volts times amps." Well then what is voltage? "Watts divided by amps." If you're a beginner to the subject, tis gets frustrating quick.
From the original complaint that started this all, we had an opening statement that was basically, "Glass is an amorphous solid that experiences a glass transition when heated. So you go to the glass transition article, and it says "he transition from a hard into a molten state." So it's synonymous with melting? (Of course not, but you have to dig really deep to find that out.) Then go to the amorphous article, and it says a solid without any long-range order. None of this tell me, the complete novice/beginner, what any of these terms actually mean.
In the welding article, I simply referred to the glass transition as a temperature range. It is much more than this, for sure, but for welding glass, all you really need to know is that it doesn't have a specific melting point, and to me that's the one key thing that really stands out. The real challenge, I think, is to define these terms as precisely, concisely, and as quickly as possible so that the reader can get the gist of what we're talking about right away. Without some context provided early on, none of the following information will make sense. Zaereth (talk) 02:29, 3 October 2015 (UTC)
I took some time over the weekend, reading a few books and trying to come up with a single sentence that explains what amorphous and glass transition mean. Even this book, Assignment of the Glass Transition, Issue 1249, although it goes into some depth on giving an "operational definition," it doesn't give a clear definition early on. Instead, it begins with an opening sentences by making a distinction between it and the other transition: "The glass transition is one of two transitions that characterize the change from a solid to a liquid; the other being the melting transition." While this is extremely vague, it does provide an idea of what it both is and is not. I think something similar could be used for the opening line of the glass transition article.
(Interestingly, the book also touches on the language problem I've mentioned: "Our language was created long before the scientific principles of many of the phenomena to be described had been understood, and changes in the meaning of a once established word, based on scientific evidence, are hardly ever possible.")
For this article (or an article on glass, the physical state), I think we should first vaguely define what a glass is before defining what glass itself is. I think it may help to take our original definition and try applying some operational definitions to the jargon. Instead of simply saying, "Glass is an amorphous solid," we could try, "A glass is a solid that has no organized, crystalline structure (amorphous solid), but rather has its atoms or molecules arranged in an overall random pattern. A glass is a phase of matter in which a material enters as it is supercooled below its melting transition and then below its glass transition, which is a radical change in material properties (hardness, ductility, formability) that occurs when a supercooled, viscous liquid becomes a solid. This glass transition typically occurs over a broad temperature range rather than a specific melting point. Instead of forming a neatly ordered, crystal lattice, the thick, viscous liquid slowly grinds to a halt to enter the solid state." Or something like that. The addition of "A" to the sentence lets the reader know we are speaking in general, not specifics.
I have to admit, I still don't understand the glass transition at all, which is why I don't meddle with the article very much. In many ways it reminds me of the martensite transformation in crystalline alloys. (I can picture crystallizing like soldiers all wandering aimlessly on a field. When the sergeant yells "A-Ten-Hut!" they all suddenly file into neat little rows. For the glass transition, the sergeant yells "A-Ten-Hut!" and everyone just slows down, but continue wandering aimlessly. Then the sergeant get's frustrated and yells "Stop!" and suddenly everyone stops right where they are.) The specifics and the science of it all are better worked out by people more knowledgeable than I, but I think an opening statement similar to what I've described will help tie it all together, so that it will be easier to understand why the material we call glass is also a glass. After that, the lede as we have it should all come together nicely. Zaereth (talk) 00:44, 6 October 2015 (UTC)
@Zaereth: Isn't your definition circular as well. You say a glass is [a] a solid that has no organized, crystalline structure [that is, an amorphous solid], but rather [b] has its atoms or molecules arranged in an overall random pattern [another definition of an amorphous solid]. Would it be better to say (for the non-scientific, 99% true definition) "Glass is a solid, hard, brittle, translucent material that is commonly transparent"? Then we could start talking about glass transitions for the formal definition.
Let's step back a few steps. First, I'm assuming that the word "transitions" in glass transitions means a phase transition, liquid-to-solid. Right? Second, are we sure that glass transitions is not another circular definition: Anything which undergoes a glass transition is glass and glass is anything that undergoes a glass transition. The lack of a definition in Assignment of the Glass Transition and other places may mean that there is no formal definition of "glass transition": the term simply means any phase transition that results in glass, which is undefined. (I'm not saying this is true, I only mention it as a possibility.)
OK, can we define glass negatively? What amorphous solids are NOT glass? Can you think of a general term or terms (as many as you like) for those solids? If so, we might be able to define glass as an amorous solid that is not (that is, does not belong to the category of) A, B or C.
I have also left a note on the WikiProject Physics talk page. Maybe a physicist can help. --RoyGoldsmith (talk) 19:04, 10 October 2015 (UTC)
A circular definition is one that uses its own word to define itself. It's like saying "Air-combat maneuvering is the art of maneuvering a combat aircraft." (Which the air combat maneuvering article actually said until a few days ago.) "Combat aircraft" is pretty clear to even a child, but "maneuvering" may not be, and certainly both of these terms need to be expanded upon in the very first sentence. It is typically not necessary to define them in great detail in the opening sentence, but rather a few synonyms or a short description of what a combat aircraft does will suffice. The opening sentence will be inherently vague, but should provide an all-encompassing definition of the subject, which provides context for the following information. So the challenge is to come up with a definition that covers all the types of glass covered in the article, which limits the definition to those two sets of criteria: that it is amorphous and that it exists below its glass transition. As mentioned above, transparency, translucency, brittleness, etc., are not all-encompassing definitions.
"Amorphous" is actually pretty simple to define, and expanding on that definition is not circular. Any 6th grade student should be expected to have a vague understanding of what atoms are, so I don't think it unreasonable to add some clarification of what "amorphous" means. My main point is that the three definitions should be listed here, in the very first sentence, because the reader should be able to read the entire article, and be able to infer all meanings directly from context, before they ever need to click on a wikilink. (See User:Zaereth/Writing tips for the amateur writer for more info.)
The big hang-up is the term "glass transition." That should be defined here, in this article, as quickly as possible. Unfortunately, as per the book I mentioned, this is very difficult to do in a single sentence, or even an entire book. However, you have to start somewhere, which leaves us the task of trying to create a vague understanding that will leave the 6th grader satisfied that they've learned something. Keep in mind that I'm only talking about the opening statement. This should, technically, be a single sentence, but in this case, may need to be a small paragraph. There is plenty of space to elaborate in the following sentences.
Once again, your definition is adequate for silicate glass. I agree with SBHarris that this article should be split, and yours would be a great opening sentence for the silicate glass article. Something like I described would be better for an article about glass (the physical state). However, as this article sits now, the opening statement should be all-encompassing, and many of the properties you've listed just are not. Zaereth (talk) 21:31, 10 October 2015 (UTC)
I'm confused. Could you provide me with some examples of NON-silicate glass, especially examples that would be recognizable, as a form of glass to layman readers? Also, what makes them NON-silicate glass? (I would say that they don't have any silicon. Or much silicon. But what do I know?) --RoyGoldsmith (talk) 20:00, 11 October 2015 (UTC)
A "glass" (in the physical sense) is a substance with no crystalline order that doesn't go through a phase change to become a solid. It just gets stiffer and stiffer as it cools, and finally hardens to a solid. A good example is whatever polymer your plastic eyeglass lenses are made of. Polycarbonate, etc. That's a non-silicate glass, a thermoplastic. You can melt it and harden it again as many times as you like. Think of acrylic glass or "Plexiglas". The plastics our manufactured world is increasingly made of, are thermosetting polymer glasses, from small item packaging to car bumpers. Of course, not all transparent. SBHarris 02:30, 14 October 2015 (UTC)
Exactly. As a physical state, a glass is one of two solid-states of matter; the other being crystalline solids. When a liquid is cooled, it eventually reaches its freezing point (melting point). At the freezing point, it crystallizes. Some materials, such as iron or copper, crystallize extremely fast, while others, like silica (sand) or honey, take a long time to crystallize. If the liquid is cooled past the freezing point before it has a chance to crystallize, it becomes a "supercooled" liquid. For example, honey's freezing point is 120 degrees F, so at room temperature, honey is a supercooled liquid. If given enough time, the honey will crystallize.
A supercooled liquid gets thick and sticky, very similar to honey in texture. (Most adhesives are supercooled liquids, which is why most tapes lose their stickiness in cold weather.) If a "seed crystal" is added, it will begin to crystallize, sometimes rather rapidly. A simple example of this is often seen in beer. If a beer is placed in a freezer for too long, it will generally become supercooled before it freezes. If you open it and take a drink, you'll notice that it is much thicker than water. Since it's far below the freezing point of water, it may freeze some of your saliva, and these seed crystals cause the beer to crystallize right before your eyes, generally within seconds.
If a supercooled liquid is cooled far enough, it reaches something called the "glass-transition temperature." Instead of a single temperature, this actually consists of a temperature range. As the supercooled liquid gets colder, it gets thicker and thicker, until the honey-like liquid is more taffy-like. At the glass transition, it begins to lose its sticky surface and starts to act more like a formable solid (plastic) than a liquid. Throughout the transition, the properties change dramatically, becoming more and more like a solid and less like a liquid. Below the glass transition, it behaves only as a solid.
Any material that can be melted or frozen can (theoretically) become a glass. Water, metals, beer, sugar, you name it, and it has the potential to be a glass if cooled under the proper conditions.
A simple experiment is to make some rock-candy. First you mix about half sugar and half water. All of the sugar won't dissolve, so you have to heat it up. Once dissolved, the liquid is cooled to room temperature, making it a supercooled liquid. Then tie a string to a sugar cube and hang it in the liquid. The seed crystal will cause the liquid to crystallize around it, and you can grow nice, big, white crystals of sugar.
Now, do it again, but add some food coloring to the liquid. After making the rock-candy, you'll find that the crystals are still white, because there was no room for the food coloring atoms to fit inside the neatly-ordered crystal. If you want to color the sugar, you have to heat it past its melting point, add some coloring, and then cool it past its glass transition to form your Tootsie-roll pop, or whatever. Cotton candy is made in the exact same way that fiberglass is made. Many, many of the common things we use everyday are physically glasses, but silicate glass (silica glass, or glass made from sand) was the original and is still the most familiar. Zaereth (talk) 07:58, 14 October 2015 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── The following is from the lead paragraph of Amorphous solid:

In some older books, the term has been used synonymously with glass. Nowadays, "amorphous solid" is considered to be the overarching concept, and glass the more special case: A glass is an amorphous solid that exhibits a glass transition. Polymers are often amorphous. Other types of amorphous solids include gels, thin films, and nanostructured materials such as glass.

This definition calls for three classifications of solids: crystalline, glass and other types of amorphous solids, such as polymers, gels and thin films. Do you agree?

If you do agree then we have a definition: Commonly, glass is any solid, hard, brittle material that is translucent or transparent. Scientifically, glass is any amorphous solid that exhibits a glass transition.

If you don't agree with the amorphous solid article then perhaps your disagreement comes from the phrase "Nowadays, amorphous solid is considered to be the overarching concept and glass the more special case". Do you disagree with that statement? Do you think we ought to change the "amorphous solid" article? --RoyGoldsmith (talk) 22:27, 14 October 2015 (UTC)

No, and here is why. Crystal quartz is solid, it's transparent, and brittle, yet it's not a glass. Porcelain (chinaware or toilets) is hard and brittle, yet is not transparent, but it is a glass. Polyethylene (sandwich bags, water bottles) is translucent, but is not hard nor brittle, and yet is still a glass. Spectralon (light reflector) is not hard, brittle or translucent, yet is still a glass. Asphalt (tar) also has none of these properties, but is also a glass. So what do all of these glasses have in common? What are the things that distinguish crystal quartz from quartz glass? Zaereth (talk) 22:56, 14 October 2015 (UTC)

Arbitrary section break[edit]

The article's lead has changed since I first broached the subject in September. The only thing I would do to it now is to move the "scientific" definition closer to the beginning. Maybe like this:
Glass is an amorphous (non-crystalline) solid which is often transparent and has widespread practical, technological, and decorative usage in things like window panes, tableware, and optoelectronics. In science, the term glass is often defined in a broader sense, encompassing every solid that possesses a non-crystalline (i.e. amorphous) atomic-scale structure and that exhibits a glass transition when heated towards the liquid state.
The most familiar, and historically the oldest, types of glass...
--RoyGoldsmith (talk) 13:29, 16 October 2015 (UTC)
That's better, but I still like the idea of explaining what the terms mean in very simple language, because the lede mainly is for the children and newcomers to the subject, or people who just want to know what the heck this term "glass" means (perhaps because they encountered it in another article and want to go back and finish reading it.) Personally, I don't like the idea of relying on wikilinks to define jargon, because it breaks the flow of reading, plus the linked articles may not provide a quick answer either (if at all), sending the reader off on a scavenger hunt for terminological definitions.
Perhaps it would be better to start from scratch. The lede really shouldn't be much more than a dictionary definition. Let me ask you this: Let's say we move the lede down into a section called "Introduction." Most technical and scientific articles should have an intro section, which is really just an expanded lede written at a high-school level (For examples, see: Alloy, Tempering (metallurgy), or Basic fighter maneuvers.) If we do this, then we have room for a lede consisting of one to three short paragraphs. Starting from scratch, how do you think we could best summarize all of this in as few words as possible --without the use of wikilinks-- and still make it understandable to the widest possible audience (not just to other scientists), assuming they have absolutely no background knowledge of the subject? Zaereth (talk) 00:04, 17 October 2015 (UTC)
Wikipedia articles are not written for young children. I think of the Wikipedia audience as intelligent high-school graduates. The word "glass" (meaning that stuff in windows and Coke bottles that you can see through) is known by virtually all kindergarteners, who can't read and are therefore not candidates for Wikipedia readership.
I think you're confusing a newspaper lede from a Wikipedia lead. See Wikipedia:Manual of Style/Lead section#Comparison to the news-style lede. WP leads are substantially longer than news ledes and should be a summary of every important section of the article, not just a definition. A summary should be concise but thorough. Leads should therefore include as many wiki-links as feasible, for conciseness. But the lead should contain nothing, except for possibly the definition, that is not restated in the detail below.
Nevertheless, I believe that the article's lead is too long. In my opinion, the way to shorten it is to reduce the sentences in each paragraph, rather than reduce the number of paragraphs in the lead. For example, does
A very clear and durable quartz glass can be made from pure silica which is very tough and resistant to thermal shock, being able to survive immersion in water while red hot. However, quartz must be heated to well over 3,000 °F (1,650 °C) (white hot) before it begins to melt, and it has a very narrow glass transition, making glassblowing and hot working difficult. In glasses like soda lime, the other compounds are used to lower the melting temperature and improve the temperature workability of the product at a cost in the toughness, thermal stability, and optical transmittance.
have to be in the lead or wouldn't it be better positioned somewhere else?
Being bold, I've changed the definition in lead paragraph. If you think it would be better the old way, please change it back. --RoyGoldsmith (talk) 19:19, 18 October 2015 (UTC)
I don't necessarily follow with Wikipedia's MOS, because it's still in its infancy. To be honest, I've never actually read it too much, because I've been doing this sort of thing since long before there was a Wikipedia. When a subject is very complex, splitting the lede and formatting in the standard pyramid structure is a very common way of delivering information. I don't edit war nor have any intentions of changing your edits. I'm just trying to offer useful suggestions in the spirit of collaboration. Just keep in mind that elementary school children (K--6) are indeed capable of reading, and understanding far more than you're giving them credit for. Wikipedia is for everybody, so there is no need to exclude a particular group. (Glass and metals have always interested me since I was very little. I rebuilt my first small engine at the age of 7, built a crossbow at 10, and forged my first sword at the age of fourteen. I read up on these things, experimented with them, and always hated those articles which condescended to me.) Zaereth (talk) 23:34, 19 October 2015 (UTC)

Lead as a network Former[edit]

Lead silicate glasses: Binary network-former glasses with large amounts of free volume

S. Kohara, H. Ohno, M. Takata, T. Usuki, H. Morita, K. Suzuya, J. Akola, and L. Pusztai Phys. Rev. B 82, 134209 – Published 29 October 2010

Shows that PbO can change to be PbO4 or 3 and act as a glass former, with up to 90mol% Pb and no phase separation. Clearly lead is more complicated that just that as a network modifier — Preceding unsigned comment added by 2001:630:12:106C:FC73:183E:A794:5102 (talk) 11:23, 13 May 2015 (UTC)

The article already mentions this in the network section. Zaereth (talk) 22:24, 7 January 2016 (UTC)