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Melting point[edit]

I was searching for the "melting point of glass" found this Wikipedia entry about Glass, but I don't appear to be able to find the actual melting point listed? I realise that the melting point will vary for different "alloys" if that's the correct term, thought it might be something useful that can be added. Name of Tony Hine, published on the 7th of August, 2012 — Preceding unsigned comment added by TØnyHine (talkcontribs) 21:14, 7 August 2012‎ (UTC)

The term "alloy" is typically applied only to metals, although metallic glasses do exist. The thing all glasses have in common is that there is no specific melting point. Rather, there is a "melting range," called the glass transition. Typically, the glass will soften as it is heated through this range between solid and a fully melted liquid. For lead glass, full melting usually occurs around 1600 degrees F, which is a glowing cherry-red color. Quartz (Fused silica) has an extremely high melting poiny of around 3000 degrees F (a "crisp your eyeballs" white-hot). Quartz also has a rather narrow glass transition, turning from solid to liquid with very little warning. Zaereth (talk) 05:20, 20 March 2013 (UTC)
From a practical (glassblower's) standpoint, melting is usually deemed to have occurred when the surface tension lowers to the point where welding can readily take place. Zaereth (talk) 18:35, 20 March 2013 (UTC)

Proofing of "state" Section[edit]

The "state" section of the article needs proofing. There is incorrect grammar. I would have made the changes but I was not allowed to see that section while in "edit" mode. — Preceding unsigned comment added by (talk) 15:31, 5 October 2012 (UTC)

I'd be happy to help, but I don't see any section titled "state" in the article. Can you provide a little more description of what needs to be changed and where? Zaereth (talk) 16:26, 5 October 2012 (UTC)
Oh, I see. It looks like Polyamorph already fixed the problem. Zaereth (talk) 19:30, 5 October 2012 (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)