Talk:Glass: Difference between revisions

	Glass is a former featured article. Please see the links under Article milestones below for its original nomination page (for older articles, check the nomination archive) and why it was removed.
	This article appeared on Wikipedia's Main Page as Today's featured article on September 17, 2004.
Article milestones Date Process Result May 3, 2004 Featured article review Kept July 21, 2004 Featured article candidate Promoted April 17, 2006 Featured article review Demoted July 28, 2006 Good article nominee Not listed Current status: Former featured article

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In the picture captioned: Hand-blown glass beads and pendants illustrate some of the myriad colors and shapes of glass art. The actual process is lampworked (also known as flameworking), not blown. I have no idea how to go about editing the main page without screwing it up, so someone more knowledgeable should change it. 68.144.87.169 05:14, 30 April 2007 (UTC)[reply]

this is gonna sound retarded to most people. but is glass a solid or a liquid? i assumed it was a solid until my science teacher (he's not one of those insane teachers, he has his facts straight) told me it was actually a super-sedated liquid. i also noticed on the page it said it was "of arguable phase". does that mean they dont know what it is? --Late Leo 20:46, 9 April 2007 (UTC)[reply]

Yes glass is a liquid but its flow speed is less than 1mm in about 100 yrs —The preceding unsigned comment was added by 84.250.110.93 (talk) 14:42, 9 May 2007 (UTC).[reply]

read the article again you might learn something...glass a does not flow at all there is no evidence of it...the anecdotes of evidence are not proof

I am desperately looking for glass properties and by properties I mean: Young's Modulus, Density, Poisson's Ratio etc. I am tempted to add space in the article and leave the values empty - could spark someone to edit it, but I supt; if you would like to see a section on the subject included, at least provide seed information that others can build upon. --Cheers, Folajimi (leave a note) 15:37, 27 September 2006 (UTC)[reply]

The Broad, Cylinder, French or German technique for making window glass is illustrated in Diderot's Encyclopedie (circa 1750-70), and can probably be dated to much earlier than that. I will try to dig up some earlier references. As an earlier author suggests, Blenko started working in West Virginia no earlier than the 1920s(?) Ids135 04:05, 22 July 2005 (UTC)[reply]

Now corrected in article Parasite 06:37, 4 February 2006 (UTC)[reply]

Question about 'crown glass process' - 9 pounds seems so - so - so random. Are there technical reasons (does it make a nice, 5' diameter circle?)? Otherwise this is a neat article which I hadn't bothered to read yet! I love the glass-flow section. I've been to the Corning Glass Museum where they not only deny it categorically but go to some length to stamp out the idea with very nice displays.--MichaelTinkler

==Would like to see some discussion of industrial uses of glass, such as for fiber optics (a very important use) and as an insulator. jimaginator

I'm not convinced by the Egyptian bit. They would not have been able to melt sand on its own (despite its ready availability!) so at the very least they must have added soda. It also seems extraordinary that they appear to have invented the float glass process millennia before Pilkington Glass of St Helens. jimfbleak 15:56 9 Jun 2003 (UTC)

The ancient Egyptian glass (circa 1500 BC) is a soda-lime-silica glass that is not that different compsitionally from modern container and plate glass manufactured today. The soda was derived from littoral natron (hydrated sodium carbonate) in which lime and magnesia were impurities. The first applications were as simulated gems then rudimentary containers. Reference: Kurkjian, Charles R. and Prindle, William R. (1998). Perspectives on the History of Glass Composition. Journal of the American Ceramic Society, 81 (4) 795-813.--tod 05:59, 29 Jul 2004 (UTC)

Mott MacDonald (http://www.mottmac.com/html/01/01_05_afr1.cfm) claim the credit for "Egypt's first float glass plant, opened in 1998". Perhaps someone should tell them! -- Heron

What is exactly the difference between "flow" and "creep"? Is it a matter of linearity of response? And then tar pitch: how is this different from glass? Isn't the fact that tar pitch flows and glass doesn't a quantitative rather than qualitative difference? -- T

Flow and creep are two different ways of looking at the same physical phenomena

The creep function describes the relation between stress and deformation

In other words creep is related to time dependent elastic constants

The word flow is usually applied to systems with constant viscosity

Here the word viscosity describes the relation between stress and deformation rate

Three things: 1. Nowhere do I see a broader definition of glass (non-crystalline solid) - this SHOULD be mentioned! 2. Everything flows at sufficient pressure/force (or decomposes). 3. Comparing glasses of different ages (eg Modern vs Egyptian) is spurious unless the chemical composition and the heat treatment is identical.DEN/3/13/2004

1. A broader definition would complicate and confuse the article. All glasses are non-crystalline (syn. amourphous) by definition. However, not all non-crystalline solids are glasses. Non-crystalline is a more general term. A definition would be good though. One possibility is the ASTM definition: A glass is an inorganic product of fusion that has been cooled to a rigid condition without crystallization. Translation: A glass is material (not based on chains or rings of carbon atoms) that has been produced by melting a liquid that was subsequently cooled to solid form without forming crystals. Note that in addition to being non-crystalline, a glass is not a polymer (plastic) but can be a metal. There exist non-crystalline polymers (i.e., polycarbonate, polymethylmethacrylate (plexiglas)), not a glass. And non-crystalline metals (metallic glasses) which are a glass. Also a glass must be formed from a molten liquid. Therefor this definition would exclude non-crystalline materials produced by other such as vapor deposition, oxidation, grinding, radiation exposure. For example, fused quartz is a pure silica glass produced by melting quartz sand and is a glass. The non-crystalline silica produced by oxidizing a silicon wafer in computer chip manufacturing is not a glass. 3. see comment above. --tod 05:59, 29 Jul 2004 (UTC)

1) In statistical physics the word glass is often used to describe a disordered system that has been cooled to a temperature where the dynamics of the system is slow compared to a given experimental timescale. Experimentalists will typically compare the relaxation time with a timescale of 100s, whereas a computer physicist will compare to much shorter timescales.In this respect the word glass is used to describe a range of systems including polymer, molten metal, supercooled organic liquids as well as the spin glass. Sometimes the term glass is used to emphasize that a system that has been kinetically trapped in a non-equilibrium state, but in other cases the term glassy response is used to describe any fast response of a viscous liquid at equilibrium. Sometimes the term ideal glass transition describes a hypothetical low temperature second order phase transition in supercooled liquids. (anonymous coward. 2 aug 04.. just added some links 17 oct)

When a solid "creeps," this refers to a permanent, plastic, time-dependant deformation that usually relies upon some applied force *usually* at high temperatures. (Think of centrifugal forces on a nickel-base turbine engine blade.) Creep for crytalline solids is heavily dependant on things like dislocations, difussion constants, Burgers vectors, and others. Flow, however, is more poorly understood for glasses. There exists only a very fine line between creep and flow, and sometimes to avoid addressing the issue, the literature will talk of "time-dependant flow" of glass. Flow depends heavily on viscosity, which is a very non-linear variable related to a exponential function of temperature. An added level of indirection is the *type* of flow, be it Newtonian or non-Newtonian, which relates to strain-rate effects. Those are questions better asked to a fluid-mechanics expert instead of a materials scientist, though.

Flow is failry well understood for glasses. Molten glass in general pretty much behaves as a newtonian liquid. The temperature dependence of viscosity is common to most all liquids. Near the glass transition temperature it is viscoelastic (which arguable can be complicated, but known), below it is an elastic solid. There are two additional situations that complicate things further. One is flow under very high strain rates as may occur during very high speed fiber drawing or very high speed press and blow manufacture (i.e. bottles). You then can run into shear thinning, a non-linear viscosity effect. Second, occurs if the particular glass composition is susceptible to phase separation (think oil and water). --tod 05:59, 29 Jul 2004 (UTC)

Re: toughened glass and laminated glass - there's no mention of a specific issue I've heard of. With large plates of toughened glass used for walls and ceilings, is there not an issue with "catastrophic failure"? A bad batch will just suddenly shatter one day, or one by one over a few days? I had heard of this as a reason for laminated glass being a safety measure - a form of backup. Is this nonsense or is it something that should be included - I don't know any facts bar what I've described. Zoney 14:23, 21 Jul 2004 (UTC)

For this reason laminated toughened will sometimes be used - the toughening process gives the glass its strength, while the PVB laminate will hold the glass in place in case of failure.

Also, there are restrictions on where toughened glass should be used - for example, in Australia it can not be used if not if the glass could fall from a 10m height above a trafficable area when shattered.

A destructive testing process called "Heat Soaking" is used to minimise spontaneous breakage. Toughened occassionaly shatters for no apparent reason, mainly due to nickel-sulphide inclusions. To reduce this risk, glass can be heated after toughening (but not greater than the annealing point). This causes any panes with nickel-sulphide stones to shatter, and the remainder are safe for use.

--Parasite 06:27, 16 Aug 2004 (UTC)

NB: Tod's comments below. This account is 'still' correct, just inverted as to compression placement at room temp. It's an important point, though. ww 16:17, 4 Aug 2004 (UTC)

The article speaks of toughened glass and this is perhaps a misnomer. An alternative term (also a misnomer in respect to tempering in ferrous metallurgy) is tempered glass. In either case, the fast cooling has the effect of solidfying (though in glasses this is itself a bit of a problem) the surface while the interior is still molten. In most glasses, solidification results in a contraction as for many other materials. This means that the outer layer of the piece goes into tension, while the inner mass (still not 'solid') is placed in compression. This situation continues even after everything has reached room temperature.

Now consider a break in the surface layer (still under tension even at room temp). The tendency will be for the break to propagate (much more so than for normal glass, which is itself quite willing to pass a crack along rather rapidly) and for the interior, being quickly relieved of its compressive strain, to expand. The result is an almost explosive release of both tension and compression and an extremely prompt shattering of the entire mass. It is indeed a catastrophic failure and if anyone was so foolish as to rely on that piece of glass for structural support of anything, well.... Even when the only structure being supported is the glass itself, the stuff is dense and can cause problems merely falling to rest if it's up in the air somewhere when it fails. Glass is not a sane structural material. But this is a good thing in some circumstances as small bits of glass are far less dangerous than large hunks, especially large falling hunks. The stuff has sharp edges, and small and light sharp edges are much less dangerous than large and heavy sharp edges when they connect with cuttable skin and eyes and ...

There are also ways to 'case harden' glass objects rather analogous to case hardening in metal work. These employ chemicals and mild heat to produce a tougher surface layer. One or another of these is common in treating glass spectacles for increased resistance to scratching and such. It is NOT the same thing/process as the forcible cooling business discussed in the article and above.

And now someone will surely ask, "what about fiberglass? Does not the glass fiber provide the strength in that stuff? Surely the binder does not, it has poor strength and toughness either in tension or compression?" And the answer is, yup, that's so. The difference is that glass is actually rather strong in tension, but never exhibits this strength in the usual case (eg, windows encountering baseballs hit by youngsters) as even minute scratches provide a focal point for strains and so are a failure waiting to happen when even the smallest additional strain is added. It's why glass is called 'brittle'. Properly produced and applied glass fibers retain much of that strength, are protected from more such scratches by the binder material in fiberglass, as well as constrained to be here and not there when the load appears, and are actually quite useful under some loading conditions.

This aspect of glass is notably missing from the article, but involves so many additional considerations (eg, failure modes, strain concentrations, etc) that I'm at a loss how to add it w/o too much increase length. Ideas anyone? ww 15:21, 23 Jul 2004 (UTC)

I would recommend just adding it, possibly under "architectural glass" - what you have written is fascinating and would make an excellent addition to the article. Length is not really a problem, certainly not for material this topical (it answers questions like "Why is broken glass dangerous?" "How do they make car windows safer?"). The fibreglass stuff might should go here in summary only and into the fibreglass article in detail, but your comments here certainly seem very apropos. --Andrew 19:08, 23 Jul 2004 (UTC)

A, One of the reasons car windows are safer is the multiple layer nature of (windshields in the US, I don't know elsewhere) as the plastic internal layer hangs onto all (most, anyway) of the sharp dangerous pieces and keeps them from flying about cutting this and that important thing. You generally get a drooping layer of plastic with sharp bits stuck to it. Much safer, if not entirely safe, and a better deal all around. Better still, of course, is to stay out of accidents altogether. ww 16:17, 4 Aug 2004 (UTC)

While you are correct that 'toughened glass' could be considered a misnomer (toughness has a specific meaning with regard to the strength of materials), tempering glass is not. In fact there are two ways to temper glass to increase its strength: thermal and chemical. Regarding thermal tempering, you are incorrect that the surface of a glass is in tension even at room temperature. On initial cooling you are correct that the surface is in tension and the interior is in compression. However, below the glass transition temperature the stresses reverse and the surface is in compression and the interior is in tension increasing the strength of the glass. Prince Rupert's drops are a laboratory curiousity demonstrating this phenomena. If a drop of molten glass is cast into a container of water, it solidifies into a shape roughly resembling a tadpole. You can bang on the big end with a hammer and the glass drop will not break. However if you nip the tail, the drop disintegrates into dust usually with a pop. Thermal tempering is usually applied to windshields. Chemical tempering is usually accomplished by ion exchanging a smaller atom for a larger atom at the surface again putting the surface in compression. Although glazing and surface crystallization can also be used. For example, soda-lime-silica glass can be placed into molten potassium nitrate and exchange potassium for sodium in the surface increasing the strength of the glass. Thermal tempering can increase the strength of glass from 70 to 200 MPa while chemical tempering can increase it 500 to 700 MPa. Chemical tempering is commonly used to increase the strength of beverage containers. --tod 05:59, 29 Jul 2004 (UTC)

Tod, You know, I've played with that tadpole drop thing, and had completely forgotten it. I stand corrected, ouch. I was inverted. And Prince Rupert's drops are a great WP article. I encourage you to creat it if it doesn't yet exist. ww 16:17, 4 Aug 2004 (UTC)

Most ordinary glass is opaque to ultraviolet light with wavelengths shorter than about 380 nm, though special glasses are made which have less transparency toward the ultraviolet.

This sentence from the article seems to be self-contradictory or confusing. Someone other than me ought to fix it. --Yath 05:49, 26 Jul 2004 (UTC)

I am really confused. A simple experiment will show the reason why greenhouses are built of glass. 1)Put a sheet of ordinary window glass between your face and the sun; you will still feel the solar radiation. 2)Put the same sheet of glass between your face and a barbeque grill; you will be shielded from the heat. Conclusion? glass is relatively transparent to ultraviolet compared with infrared. Will someone with more knowledge than I have please explain the discrepancy? Too Old 17:04, 17 Sep 2004 (UTC)

Yes you can feel the solar radiation through glass. But since most of the power is in the visible, that would be true independent of whether or not it passed any ultraviollet at all. The conclusion you have doesn't follow from the given experiment. The correct conclusion for that experement (if the facts are as reported) is that glass is more transparent in the visible than in the infrared. Nahaj 01:52, 23 April 2006 (UTC)[reply]

Heat is transmited by convection/conduction as well as from radiation. In your experiment, the glass sheet shields you from the *hot air* coming from the grill. This is not relevant in experiment 1, where air at both sides of the sheet is at the same temperature. -- T

This confusion probably arises from the undefined term 'ordinary glass.' I suspect what was meant was the family of glasses based on the 1:1:6 soda-lime-silica composition (roughly 14 Na2O, 12 CaO, 75 SiO2 on a weight percent basis) that is nearly ubiquitous in the manufacture of clear container and window (plate) glass. The UV cutoff wavelength of glass is primarily composition dependent. Pure silica (100% SiO2) glass can have a UV cutoff below 200 nm, while glasses containing, for example, ceria (CeO2) or titania (TiO2), will shift the cutoff to wavelengths below 380. If enough of these oxides are added the cutoff will shift to wavelength below 400 nm which will manifest itself as a coloration of the glass as the blue end of the visible spectrum is absorbed along with the UV.

Which brings up my main criticism of the article. There are many instances of vague or undefined terms such as 'common', 'pure', and 'ordinary' that can be confusing without context. --tod 05:59, 29 Jul 2004 (UTC)

Agreed, why do we mention cerium as preventing UV stuff, when it said it blocks all, etc... Some clarity on this would be nice. -- ~ender 2005-02-13 11:18:MST

Here is the diff. I removed it not because I thought it was accurate or inaccurate, but because this thing is going to be on the main page tomorrow (Sep. 17) as a featured article and I'm not comfortable trying to rework or incorporate it in such a short amount of time. Can someone else tackle this? --Ardonik.talk() 19:32, Sep 16, 2004 (UTC)

Well, I was the one who put it in - I am a glassblower. But what I find interesting is that any corrections I have made simply disappear. For example, if this is a feature page - William Blenko did not invent cylinder glassblowing in the early 1900's, it was used decades before - yet the misinformation appears nice and clean on a feature page.

I don't see any mention of crystal glass in the article, and I don't quite know how I could fit it in, does anyone care to do so? 3:56 UTC 17-Sept-04

The heading 'Arguments against glass flow' seems to imply that the question of glass flowing is contraversial. If this is the case, the article should make that more clear IMHO and have a "for glass flowing section". If this is not the case, the heading should reead "Evidence against glass flow", not "Arguments" Bletch 12:32, 17 Sep 2004 (UTC)

Okey, glass is not flowing.

But is it a liquid? I think that, but I am not sure. But it would be important to include that in the article (whether or not it is) It _is_ a liquid if there is no first order phase transition between room temperature and high temperatures, and the decrementation of viscosity is continual.

So..?

It is my understanding that glass is indeed a liquid. Glass knives are frequently used to process samples for electron microscopy. Only freshly made knives are sharp enough due to the liquid nature of the glass.

Try using fused quartz instead. Flint glass undergoes some (highly localized) dissolution in water, because of minute fluctuations in sodium and calcium content: this is probably what causes your knives to dull.--Joel 00:36, 24 Apr 2005 (UTC)

My understanding is that glass is a liquid at room temperature. The arguements that older glass (Midevel, etc.) are irrelevant as the flow rate is so low that event that time frame is not sufficient for the glass to lose its shape. Its a liquid we treat as a solid, but that doesn't make it so. Bismuth is radioactive, but at least one isotope we treat as if it isn't (sorry, I can't remember which one). It's half-life is much longer than the age of the universe, but it is radioactive. I encourage the reader to check out the Straight Dope Archives on this one at glass which I'm going to add to the main article. Rt66lt, August 5, 2005

Not a physicist or chemist, but I've seen it said glass is "extremely low viscosity liquid". Comment? Trekphiler 05:27, 9 December 2005 (UTC)[reply]

For what its worth, one of my chemistry professors at UC Berkeley referred to glass as a liquid in passing and it struck me as odd so it stuck with me. Also, I've seen documentaries on the world's largest telescopes (located in Hawai'i and owned by the UC system as I recall) which noted that larger lenses were impossible to make since the glass would "pour" and distort images too much. BoomBox 17:08, 7 January 2006 (UTC)[reply]

If you wish to discuss if glass is a liquid, then you must use the terminology of glass physics.

1) The wikipedia page defines liquid to be one of the four phases of matter. This definition is of course correct and very useful, but it does not apply to silicate glass at room temperature. The problem is that if you define the word liquid in terms of a phase diagram, then you are only able to treat equilibrium states.

2) In glass physics a sample is usually defined to be liquid if the viscosity is smaller that 10^12 Pascal seconds, or if the ratio between viscosity and instantaneous shear modulus is smaller than 100s. These definitions are practical as they allows you to compare the glass transition temperature of different chemical compositions, and I pressume that they are also used in the glass industry. Strictly speaking the term viscosity is an equilibrium property, and therefore the viscosity of a non-equilibrium states is only welldefined within models. However I still think that it is fair to use this definition to rule that silicate glasses at room temeprature are not liquids.

3) You asked for a thermodynamical definition: Sometimes the term liquid is used to describe a sample at equilibrium, whereas the term glass is used to described a system that is frozen in a non-equilibrium state (Here I mean frozen within a suitable experimental timescale). In other words the term glass is usually defined to be the opposite of a liquid. It is correct that in a phase diagram the boundary between the liquid phase and the glass phase is not a phase transition. Instead it marks the temperature where the system leaves equilibrium. (Actually it is very dangerous to draw this kind of phase diagrams, because the boundary between liquid and glass depends on the cooling rate). Anyway silicate glass at room temperature has been frozen in a non-equilibrium state and therefore it is not a liquid.

BTW: The article describes that additives are added to lower the melting temperature. I don't think that this is correct. The the word melting temperature refers to the temperature at which the system can crystalize. In other word the sample is supercooled whenever it is cooled below the melting temperature. HOwever temperature is unimportant for the production process, so there is no reason to try to change it. I would pressume that the additives are added to lower the Glass_transition_temperature.

The article seems to imply that silica glasses are not supercooled at room temperature. I have a feeling that this is wrong. At least it is inconsistent with the claim that system has a melting temperature of 1000 K. The sentence should probably be double checked or deleted.

The article describes the ability of some glasses to block UV light, which is parenthetically described as "ionizing radiation." It is my understanding that the term 'ionizing radiation' usually applies to high-energy particles resulting from radioactive decay, or electromagnetic radiation at frequencies higher than UV, such as x-rays or gamma rays. Although the article is correct in saying that UV may be biologically harmful, it may not be accurate to describe the UV blocked by glasses as 'ionizing radiation.'

No, ionizing radiation is anything with enough energy to ionize an atom/molecule, i.e. to break a bond. Look at Ultraviolet#Health effects for confirmation that UV does indeed have this property. You're right, however, that most other forms of ionizing radiation are more energetic, and many can pass through glass quite easily, especially if there's no lead or uranium in the mix.--Joel 01:08, 24 Apr 2005 (UTC)

Hello. As a casual reader, I find the following two statements a little confusing. They do not seem to be consistant:

• From the 3rd paragraph in the introduction: Pure silica has a melting point of about 2000 °C (3632 °F), so two other substances are always added to the sand in the glass-making process. One is soda (sodium carbonate Na2CO3), or potash, the equivalent potassium compound, which lowers the melting point to about 1000 °C. However, the soda makes the glass water-soluble, which is obviously unhelpful, so lime (calcium oxide, CaO) is the third component, added to restore insolubility.
• From the 3rd paragraph in the Overview: Sodium is generally used to lower the otherwise impossibly high (when glass was first discovered) temperatures needed. Additional soda or potash is sometimes added to further lower the melting point.

I think this should be cleaned up. I don't know anything about glass making, so I am not making this change. -- JamesTeterenko 22:33, 17 Sep 2004 (UTC)

I gave it a once over. See what you think.--Joel 01:24, 24 Apr 2005 (UTC)

The melting points of various kinds of glass are wellknown. Therefore it is well known that all glass is supercooled at room temperature.

It is not controversial to write that glass is supercooled at room temperature is supercooled. It would be wrong (and thus controversial) to say that windows glass is a liquid at room temperature. The information of glass being supercooled It is not relevant to to question of whether or not windows flow.

The introduction of the article is inconsistent. First you write that glass is transparent, and then you write that the term glass is used to describe any substance thats is cooled below the glass transition temperature. This definition also includes some liquids that have a color. Later again you introduce terms like common glass and ordinary glass without definition. How about adding the following sentence instead.

"In physics the term glass often refer to an amorphous solid or a liquid that is cooled below the glass transition temperature." --- Following the format of other Wikipedia articles, I moved the physical definition of a "glass" to the top, gave an example, then stated that the remainder of the article is concerned with the common definitiono f "glass"

I've just noticed that the section on Self-cleaning glass starts: "A recent innovation—once more from Pilkingtons" yet there are no other references in the page to Pilkingtons. Is this a reference to something that was once but is no longer in the article; a subtle peice of self-advertising; or something else entirely? 192.171.162.101 16:28, 31 Jan 2005 (UTC)

Well Alastair Pilkington is famous for the invention of float glass. Both he and the family business are in fact mentioned in that section.

I think the problem is that the company may have changed its name several times over the past couple of decades. I'm pretty sure it used to be called Pilkington Glass and it now seems to be just Pilkington, but there is a good chance that it was called Pilkingtons with the extra 's' some time in between (not that the article on Pilkington Glass tells you much). -- Solipsist 17:36, 31 Jan 2005 (UTC)

Thanks for the info! I've replaced "Pilkingtons" with "Pilkington Glass" now; hopefully I'll be the last person confused by this :O) (the same person, now no longer at work) -- Whitepaw 19:29, 2005 Jan 31 (UTC)

Pilkington Glass are based in St. Helens (my hometown), and as a "short" they are known as "Pilks". As in "something is going on at Pilks". In the same respect "Pilkingtons" is used when referring to something they're doing or is happening to them. S'just a colloquial habit. Koncorde--82.42.56.236 17:51, 22 May 2006 (UTC)[reply]

"This section is an argument in favor of a position; it does not belong as part of a reference work. The statement that glass is a supercooled liquid refers to the lack of a specific melting point for glass, not to any perceived rate of 'flow', so the argument that follows is meritless."

I want to remove this sentence, but I imagine there might be some controversy behind it? - Omegatron 00:05, May 16, 2005 (UTC)

No harm in toning down the rhetoric to be less aggressive. If that editor comes back and yells "I wanted it to make prior editors feel like dirt! It has to be worded my way! Change it back, you moron!" then it will be safe to remove the statement entirely. One thought is that you might reword it to clarify that the argument is meant to combat the common misconception that old panes of glass have flowed since installation etc. etc.--Joel 07:57, 16 May 2005 (UTC)[reply]

It was changed by someone else, but a bunch of information was removed? - Omegatron 17:35, May 18, 2005 (UTC)

The fact that glass "creeps" doesn't really belong in the room temperature flow argument, because (as a previous editor neglected to mention) creep is a response to high temperature as well as stress. From the standpoint of fundamental physics, it is the same glass-transition behavior discussed above. We can probably debate about the suitability of newsgroup discussions as reference material, however.--Joel 18:12, 18 May 2005 (UTC)[reply]

aha! there are two different types of movement being discussed! this should be more obvious, methinks. - Omegatron 19:42, May 18, 2005 (UTC)

I was the one who removed it. I rewrote the whole section. I was being bold. Change back whatever you think I overstepped. moink 03:39, 19 May 2005 (UTC)[reply]

The new section title, "The myth of glass being liquid at room temperature", seems clunkier than the previous, "Does glass flow?". —wwoods 23:15, 18 May 2005 (UTC)[reply]

Yeah, it's clunkier but more accurate (i.e., there's no real debate). Change it to something simpler if you like. moink 03:39, 19 May 2005 (UTC)[reply]

I've edited the introduction to the article (mostly new headers and a reorder of some material) to make it easier to read. Also there was some repetition of information and a little too much detail in the first section. Possibly still needs some work though. clare

I asked about this on the Reference desk. Some useful information was turned up, it should be merged into the article. The question, and answers, are here: Wikipedia:Reference_desk_archive/Humanities/August_2005#Invention_of_glass_blowing.3F. JesseW, the juggling janitor 04:55, 6 September 2005 (UTC)

An anonymous user wrote:

but it can also be argued that glass formed at different places on the planet can vary in composition or certain subtle variations in composition which lead to differences in viscocity.may be roman and egyptian glasses have a really large viscocity than that of other glass made in the current world. (sic)

In fact, differences in viscosity are most prominent in different types of glass: GeO2 is much thinner than any alloy of SiO2 (no matter where or when it was made), and, as the article mentions, even GeO2 is so viscous at room temperature that the time interval to regard it as a liquid would span 10³² years, which you should compare to the 10² to ⁴ years that a civilization tends to last.--Joel 17:56, 8 November 2005 (UTC)[reply]

The page says: "Obsidian collection is prohibited by law in some places...". This seems unlikely. It has been suggested on Talk:Obsidian that the actual prohibition is of collection of obsidian artifacts. It would be good if somebody could find out for sure and update this page. EdDavies 22:55, 17 November 2005 (UTC)[reply]

http://www.colossal-fossil-site.com/475-legislative/36-BLM-regs-state.htm says it varies state to state, i changed it to hopefully make some more sense, why on earth would collecting rocks be illegal?!?

The obsidian cliff in Yellowstone is almost gone now, hauled off in bits and pieces illegally by tourists. Note that rock collecting is illegal in many (if not most) [US] National Parks, along with collecting plants without authorization, etc... Nahaj 04:28, 4 April 2006 (UTC)[reply]

N really sure if it belongs here (doubt it), but, anybody care to try explaining how it's made? (If you don't know, it's the stuff Hollywood uses for stunt windows.) Trekphiler 05:30, 9 December 2005 (UTC)[reply]

They just melt sugar (probably a special transparent type) and pour it in a mold of the shape they want the glass to be. Then they just wait till it cools.Slartibartfast1992 01:25, 6 December 2006 (UTC)[reply]

Added that section under ingredients. I would like to add some reference to sol gel as well

LaoAn 21:45, 26 December 2005 (UTC)[reply]

the little pro/con argument at the bottom of the article is misleading. By investigating the links at the bottom of the page, one can quickly learn that glass is not a liquid, and as such, will not flow. Some glass can be adulterated with minerals to cause it to become softer.

look at the USENET article, Original by Philip Gibbs October 1996.

should not any suggestions that glass is a liquid and flows, be removed? I think so.

Glass is an amorphous solid and will flow beause of the characteristics of this type of solid.Slartibartfast1992 01:26, 6 December 2006 (UTC)[reply]

It does not mention in the article, but I believe glass is naturally a hydrophillic material, as the contact angle is small with water. Also glass can be etched by some chemicals like hydrofluoric acid, so it isn't 100% inert... something to note?

An interesting question which I would like to have answered here is why glass is so unreactive. – gpvos (talk) 12:54, 12 March 2006 (UTC)

"Ordinary glass does not allow light at a wavelength of lower than 400 nm, also known as ultraviolet light or UV, to pass."

To my knowledge UV-light can be subdivided like so:

UVA 400 nm - 320 nm UVB 320 nm - 290 nm UVC 290 nm - 100 nm

Of wich UVA passes through windowglass, and UVB and UVC being absorbed (or reflected I don't know). If that's true, then glass is not completely impenetrable by UV light. Any comments?(MrDeBeuker 11:21, 4 February 2006 (UTC))[reply]

See this link: [1] virtually all common glasses have this absorption curve of allowing a majority of light above 300nm in the UVA and blocking virtually all light below 300nm. Actually glass blocks partially light between 300nm and 400nm. Mr.K. 03:38, 28 February 2006 (UTC)[reply]

what non-silicate glass is there?

Chalcogenide glass Bridesmill 03:51, 27 May 2006 (UTC)[reply]

Has anyone else looked at the french and german counterparts to this article? I have to say that both look far better in terms of broad coverage of the science and the history of glass especially wrt to illustrative images. This aricle imho should definitely look to those two for ideas on improvement.--Deglr6328 17:43, 6 May 2006 (UTC)[reply]

I have no scientific knowledge relavant to any debate over the definition of a liquid or whether glass falls into any such definition. However, it is clear to me as a reader that the article itself coyly avoids answering the question. This is unacceptable. The article should do one of three things: say that glass is not a liquid; that is a liquid (albeit one that is more viscose than the cathedral glass myth would suggest); or that this is something of a 'grey area' and it depends on the definition of 'liquid' adopted. Currently, some statements in the article imply, at least to someone like myself who doesn't already know the answer, that glass is a solid:

• " One common misconception is that glass is a super-cooled liquid ... "
• "The result is a loss of focus, and occurs not because the glass is flowing over time..."

Whereas other statements suggest to me that glass might be a liquid:

• "If medieval glass has flowed perceptibly" - implying that it does flow slightly. If there is no flow at all then this is otiose: it would only be necessary to state that glass does not flow, 'period'.
• Ditto: "If glass flows at a rate that allows changes to be seen"

And other statements suggest the problem is partly definitional: "he wrote that glass at room temperature is very strongly on the solid side of the spectrum from solids to liquids."

So please - people who know what they are talking about - either come to a consensus on whether the glass is liquid or solid, or, if there are definitional problems, make this clear. The section as it currently stands is very poorly written. --Danward 17:56, 14 May 2006 (UTC)[reply]

Try looking here: Glass: Liquid or Solid -- Science vs. an Urban Legend, then write it in yourself. See WP:BOLD --DV8 2XL 19:04, 14 May 2006 (UTC)[reply]

Grr - OK, I've had a shot at it. In fact, I've found another well-written source on the subject (which is linked in the new text) which suggests that the whole topic is fiendishly complicated, that there is scope for different views and even that "There is still much about the molecular physics and thermodynamics of glass that is not well understood": [2]. I'd suggest that anyone who wants to attack or improve upon what I've written takes a peek at that paper, because it canvesses a variety of views and aspects of the problem. --Danward 22:24, 14 May 2006 (UTC)[reply]

The section is already rather big and quite specific for a general topic. Please consider a summary-style split into a separate Is glass a super-cooled liquid? main article. Femto 11:56, 15 May 2006 (UTC)[reply]

That's a fair point actually. I'll look into it when I've got a free moment unless someone else writes it. --Danward 22:26, 16 May 2006 (UTC)[reply]

Following the most recent changes to this section (which generally seem to be good improvements), it now states "Glass is most commonly classed as a liquid..." Is there a clear basis for saying that it is *most* commonly so regarded? I would have thought that given this page until recently adopted the line that it was an amorphous solid 'no question', the most one could say would be that glass is "commonly" treated as a liquid (?) --Danward 00:00, 20 May 2006 (UTC)[reply]

The reference to pitch clouds the subject considerably. To me 'pitch' isn't a solid by any definition in my head, if someone mentioned it to me I would reference it alongside 'tar' which also isn't a solid. There is no quantified evidence to prove glass has ever flowed once at room temperature under normal conditions. Not a single mention of experiments to deform glass using weights. In conclusion - just because glass doesn't form a perfect rigid lattice structure doesn't mean it isn't a solid (albeit not a solid by 'junior physics' standard, which appears to be the standard used by far too many websites on the web proliferating the myth lacking an understanding of thermodynamics). There are two main websites that deal with the Legend in an adult fashion and both conclude that it is an AMORPHOUS SOLID. they are http://math.ucr.edu/home/baez/physics/General/Glass/glass.html and http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html and here's the debunking of a person who is clearly teaching junior physics to juniors http://www.newton.dep.anl.gov/askasci/chem99/chem99017.htm (again proliferating the myth - he even says "we all know", but is wrong). http://www.sciencenews.org/pages/sn_arc98/5_30_98/fob3.htm and here again in the American Journal of Physics. Anyone who has read The Science of Discworld books will realise the 'glass as a liquid' is one of those "lies to children" because explaining the truth is far too complicated and would contradict everything you've just said. Any scientist worth his salt would define glass as an amorphous solid, or at least explain that it does not fall within the 'traditional' 2 form boundaries which we created as an easy guide for kids (not for the molecular dissection of every object on earth). - Koncorde --82.42.56.236 14:52, 22 May 2006 (UTC)[reply]

Right now the first paragraph says "Clearly, glass is a liquid, since cathedral windows are always much thicker at the bottom." I was under the impression that this was blatantly untrue, and so is a paragraph nearer the bottom of the article. I'd like to at least see the article agree with itself.

I'm in the process of editing the history section of this article in my sandbox. More specifically I'm adding new material and tracking down references. Hopefully I will have this completed sometime next week.

Baudoin 19:58, 17 May 2006 (UTC)[reply]

The edit is complete and has been uploaded. ````

The observation that old windows are often thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a matter of centuries. It is then assumed that the glass was once uniform, but has flowed to its new shape.

The likely source of this belief is that when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the Crown glass process, described above). This plate was then cut to fit a window. The pieces were not, however, absolutely flat; the edges of the disk would be thicker because of centrifugal forces. When actually installed in a window frame, the glass would be placed thicker side down for the sake of stability and visual sparkle. Occasionally such glass has been found thinner side down, as would be caused by carelessness at the time of installation.

I totally learned something new today. much appreciated. -Taco325i 02:55, 20 July 2006 (UTC)[reply]

Some person keeps adding a sentence that glass does not have infinite viscosity. This statement is not true. A solid is per definition definition a system with infinite or very high viscosity (See [glass transition temperature]]).

The following article is a standard refence on flow of glass windows. It is coauthored by following article by Prabhat Gupta who is one of the leading experts in the field. (Sadly it requires subscription)

Edgar D. Zanotto and Prabhat K. Gupta American Journal of Physics -- March 1999 -- Volume 67, Issue 3, pp. 260-262 http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000067000003000260000001&idtype=cvips&gifs=yes

The article makes use of a model called the Tool_Narayanaswami_model, which is arguably not perfect, but at present this model is the best model that we have.

The point of the article is that window glass does indeed flow, but the flow rate is so slow that it cannot explain the shape of cathedral windows. In other words window glass can be treated as a solid (with infinite viscosity) for all practical purposes. The viscosity of window glass at room temperature is indeeed much higher than pitch.

But when you make this statement you have to be careful to use the right words. The word supercooled liquid is a technical term, and it is routinely applied to systems with a very large viscosity. Over the last few decades a lot of people have tried to model what would happen if we could equilibrate a supercooled liquid far below the glass transition temperature. (See the article about the [Kauzmann_paradox]]). In this context the term super cooled liquid is applied systems with a very high viscosity. In other words the same system can be a supercooled liquid as well as an amorpheus solid.

Any further information for the above appreciated (or merge to this page if appropriate) Jackiespeel 18:40, 27 July 2006 (UTC)[reply]

The Good article nomination for Glass has failed, for the following reason:

Lack of citations. Just three? There are lots of statistics that need citing, but what was brought to my attention was the uranium-added glass. More citing, and then it should pass. Iolakana|^T 18:10, 28 July 2006 (UTC)[reply]

I would decide how you want a spell color/colour. The article tends to flip-flop. Just a suggestion. MJCdetroit 13:43, 15 September 2006 (UTC)[reply]

I have changed all text reading colour to color except where calling up an External Link / Reference where I retained the original. I chose the AmE as this is what the original article was written in circa. 2001. Parasite 08:06, 18 September 2006 (UTC)[reply]

Um, how many citations does it have currently? i don't know, but it looks like something at least 9. Duinemerwen 02:34, 19 December 2006 (UTC)[reply]

The article needs more information about laminated glass and various other types of glass. For example, the treated (laminated?) glass used in automobiles, trains and so on (in romanian it's called "geam securizat" direct translation to english: secured glass, I don't know the correct english translation) Persons interested in expanding this may find the following site usefull: http://www.glassonweb.com/glassmanual/index.php Mariushm 19:50, 8 December 2006 (UTC)[reply]

Well I heard that glass made with lead generally has 12-25% lead content, depending on how much shine is desired. Anyway, my question here is lets say a glass cup contains 20% lead content, wouldn't that be dangerous to the body and brain to use a cup like that? And will consuming alcohol from a glass cup like this have any effect on the lead? Because I heard some wine bottles stored in lead glass can become contaminated. I'm guessing if lead/glass does get into the body then is probably insignificant and next to nothing, but what about over the course of a lifespan? I don't want to get alzheimer's when I'm older. —The preceding unsigned comment was added by 75.84.4.168 (talk) 03:10, 15 February 2007 (UTC).[reply]

A section named Calculating Glass Properties has just been added. I think it's way too near the top of the article, if it's even relevant at all.Joelholdsworth 09:12, 16 February 2007 (UTC)[reply]

I was in Australia for a couple of weeks and visited a friend there.

He's working in a glass-bottle factory in Penrith and took us on a tour. (very interesting I might add).

He told us, that glass could contain almost anything. The only substance/liquid it couldn't contain was - and I might have had a problem hearing hip, there was quite noisy in there - Goana Oil. The molecules of that particular oil was simply so small, that the molecules of the glass couldn't contain them, and it would simply flow out of the jar/bottle.

Now, I've never heard of Goana Oil and forgot to ask him further. Can I have misheard him and it's actually something else or?

Is there any other substance glass can't contain?--Nwinther 13:57, 28 February 2007 (UTC)[reply]

Hydroflouric acid dissolves glass (albeit slowly), and thus cannot be contained by it for more than a short time. Not the same deal as what you were told, but it's something that glass can't contain. Someguy1221 16:46, 22 March 2007 (UTC)[reply]

Refer to Australian humour, particulary An important aspect of Australian English usage, inherited in large part from Britain and Ireland, is the use of deadpan humour, in which a person will make extravagant, outrageous and/or ridiculous statements in a neutral tone, and without explicitly indicating they are joking. BTW, Goanna oil is similar to Snake oil. :) Parasite 23:43, 28 February 2007 (UTC)[reply]

Quote: > Strangely enough, to make good quality glass, you need to ADD glass to the mixture (or cullet) before it gets to the molten tin furnace to float on. Tin when molten is perfectly flat and glass floats on top as it is lighter than tin, thus giving glass the "float glass" name sometimes used instead of "raw glass".

The whole wording makes me uneasy, but we need supporting evidence first before we talk about cleaning up the wording. As a matter of fact, does the article really need to explain in this much detail how to make glass? —The preceding unsigned comment was added by 204.96.216.30 (talk) 13:13, 1 March 2007 (UTC).[reply]

The discussion of UFOs in the Americas and their connection to glass seems to me rather speculative. It should probably be removed if no reliable source can be found.

"Reduction of the sum of square errors using the Solver option in Microsoft Excel with the glass components as variables" - is Excel uniquely good for this? Otherwise it doesn't seem neutral to mention a specific piece of software.

A couple of months ago, with this edit: [3], a big chunk of useful and readable info on glass properties and ingredients was removed and then replaced with the way-too-technical "calculating glass properties" section. The info should really be re-integrated back into the article, and the calculations shunted into some other article. --Bob Mellish 08:15, 15 April 2007 (UTC)[reply]

Oh you haven't noticed? no one notices/gives a shit. this happens everywhere all the time. I'm close to leaving wikipedia due to the ceaseless unchecked vandalism.--Deglr6328 02:55, 4 July 2007 (UTC)[reply]

So far as I can tell, there does not seem to be an extant project which deals with this article, or several other similar articles. On that basis, I have proposed a project at Wikipedia:WikiProject Council/Proposals#Chemical compounds and mixtures which might deal with subjects such as this. Anyone interested should add their name there so that we can know if such a proposal would receive sufficient interest to at least potentially stay active. Thank you for your attention. John Carter 16:38, 30 April 2007 (UTC)[reply]

I came to this article to find out how glass is made, and was surprised that it does not explain the production process, only the composition. I think this would be very useful information to include. Thanks. 134.225.1.162 12:56, 15 May 2007 (UTC)[reply]