Jump to content

Glass: Difference between revisions

Edit links
From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
ClueBot (talk | contribs)
1,596,818 edits
m Reverting possible vandalism by 75.108.242.28 to version by LindsayH. False positive? Report it. Thanks, User:ClueBot. (316111) (Bot)
←Replaced content with 'i'VE TAKEN THE LIBERTY OF REMOVING THIS IRREVLEVANT BLOG. glass does not exist!'
Line 1: Line 1:
i'VE TAKEN THE LIBERTY OF REMOVING THIS IRREVLEVANT BLOG. glass does not exist!
{{this|the material}}
[[Image:Moldavite Besednice.jpg|thumb|right|[[Moldavite]], a natural glass formed by [[meteorite]] impact, from [[Český Krumlov District|Besednice]], [[Bohemia]]]]

[[Image:RHSGlasshouse.JPG|thumb|right|A modern [[greenhouse]] in [[Wisley Garden]], [[England]], made from [[float glass]]]]

[[Image:Gluehlampe 01 KMJ.jpg|thumb|right|upright|Clear glass [[Lamp (electrical component)|light bulb]]]]

'''Glass''' in the ''common'' sense refers to a [[hard]], [[brittle]], [[transparency (optics)|transparent]] [[solid]], such as used for [[window]]s, many [[Glass Bottles|bottles]], or [[eyewear]], including [[soda-lime glass]], [[acrylic glass]], [[sugar glass]], [[Muscovite|isinglass]] (Muscovy-glass), or [[aluminium oxynitride]].

In the ''technical'' sense, glass is an inorganic product of fusion which has been cooled to a rigid condition without crystallizing.<ref>[[ASTM]] definition of glass from 1945; also: [[Deutsches Institut für Normung|DIN]] 1259, Glas - Begriffe für Glasarten und Glasgruppen, September 1986</ref><ref name=Zallen83>Zallen, ''The Physics of Amorphous Solids'', John Wiley, New York, (1983).</ref><ref name=Cusack87>Cusack, ''The physics of structurally disordered matter: an introduction'', Adam Hilger in association with the University of Sussex press (1987)</ref><ref name=Elliot84>Elliot, ''Physics of amorphous materials'', Longman group ltd (1984)</ref><ref>Horst Scholze: "Glass - Nature, Structure, and Properties"; Springer, 1991, ISBN 0-387-97396-6</ref> Most glasses contain [[silica]] as their main component and ''glass former''.<ref name=vogel>Werner Vogel: "Glass Chemistry"; Springer-Verlag Berlin and Heidelberg GmbH & Co. K; 2nd revised edition (November 1994), ISBN 3540575723</ref>

In the ''scientific'' sense the term glass is often extended to all [[amorphous solid]]s (and melts that easily form amorphous solids), including [[plastic]]s, [[resin]]s, or other silica-free amorphous solids. In addition, besides traditional [[Glass_production#Hot_end|melting]] techniques, any other means of preparation are considered, such as [[ion implantation]], and the [[sol-gel]] method.<ref name=vogel/> However, ''[[:Template:Glass science|glass science]]'' commonly includes only [[inorganic]] amorphous solids, while plastics and similar organics are covered by [[polymer science]], [[biology]] and further scientific disciplines.

The optical and physical properties of glass make it suitable for applications such as [[flat glass]], [[container glass]], [[optics]] and [[optoelectronics]] material, [[laboratory equipment]], thermal insulator ([[glass wool]]), reinforcement fiber ([[glass-reinforced plastic]], [[glass fiber reinforced concrete]]), and [[Glass art|art]].

== General properties, uses, occurrence ==
[[Image:Erlenmeyer flask.jpg|thumb|right|upright|[[Laboratory glassware]] made from [[borosilicate glass]] ([[Erlenmeyer flask]])]]

[[Image:502px-TFT Monitor Flachbildschirm.jpg|left|thumb|[[Flat panel display]], using thin sheets of special [[alkali]]-free<ref>See article: [[Samsung Corning Precision Glass]], TFT-LCD Glass substrates</ref> glass]]

Ordinary glass is prevalent due to its transparency to [[visible light]]. This transparency is due to an absence of electronic [[transition state]]s in the range of visible light. The homogeneity of the glass on length scales greater than the [[wavelength]] of visible light also contributes to its transparency as heterogeneities would cause light to be [[scattering|scattered]], breaking up any coherent image transmission. Many household objects are made of glass. [[Drinkware|Drinking glasses]], [[Bowl (vessel)|bowls]] and [[Glass bottles|bottles]] are often made of glass, as are [[light bulb]]s, [[mirror]]s, [[aquarium|aquaria]], [[cathode ray tubes]], computer [[flat panel display]]s, and [[window]]s.

In research [[laboratory|laboratories]], [[laboratory flask|flasks]], [[test tube]]s, and other [[Laboratory glassware|laboratory equipment]] are often made of [[borosilicate glass]] for its low [[coefficient of thermal expansion]], giving greater resistance to [[thermal shock]] and greater accuracy in measurements. For high-temperature applications, [[Fused quartz|quartz glass]] is used, although it is very difficult to work. Most [[laboratory glassware]] is [[mass-production|mass-produced]], but large laboratories also keep a [[glassblowing|glassblower]] on staff for preparing custom made glass equipment.

Sometimes, glass is created naturally from volcanic [[lava]], [[lightning]] strikes, or [[meteorite]] impacts (e.g., [[Lechatelierite]], [[Fulgurite]], [[Darwin Glass]], [[Volcanic Glass]]). If the lava is [[felsic]] this glass is called [[obsidian]], and is usually black with impurities. Obsidian is a raw material for [[flintknapper]]s, who have used it to make extremely sharp [[glass knife|glass knives]] since the [[stone age]].

Glass sometimes occurs in nature resulting from human activity, for example [[trinitite]] (from nuclear testing) and [[beach glass]].

===Glass in buildings===
{{main|Architectural Glass|Glazing in architecture|Window}}

[[Image:flats at bristol harbour arp.jpg|thumb|right|Extensive use of [[float glass]] sheets in apartments in [[Bristol]], [[England]].]]

Glass is commonly used in buildings as transparent windows, internal glazed partitions, and as architectural features. It is also possible to use glass as a structural material, for example, in beams and columns, as well as in the form of "fins" for wind reinforcement, which are visible in many glass frontages like large shop windows. Safe load capacity is, however, limited; although glass has a high theoretical yield stress, it is very susceptible to brittle (sudden) failure, and has a tendency to shatter upon localized impact. This particularly limits its use in columns, as there is a risk of vehicles or other heavy objects colliding with and shattering the structural element. One well-known example of a structure made entirely from glass is the northern entrance to [[Buchanan Street subway station]] in [[Glasgow]].

Glass in buildings can be of a safety type, including wired, heat strengthened (tempered) and laminated glass. Glass fibre insulation is common in roofs and walls. Foamed glass, made from waste glass, can be used as lightweight, closed-cell insulation. As insulation, glass (e.g., [[fiberglass]]) is also used. In the form of long, fluffy-looking sheets, it is commonly found in homes. Fiberglass insulation is used particularly in attics, and is given an R-rating, denoting the insulating ability.

===Technological applications===
[[Image:OpticsGlass.jpg|thumb|right|Uses of glass for scientific purposes range from applications such as [[DNA microarray]]s to large sized [[neodymium]] doped glass [[lasers]] and glass fibres]]

[[Image:Hubble 01.jpg|thumb|left|The [[Hubble Space Telescope]] orbiting above earth, containing [[optical instrument]]s]]


Pure [[Fused quartz|SiO<sub>2</sub> glass]] (the same chemical compound as [[quartz]], or, in its [[polycrystalline]] form, [[sand]]) does not absorb [[UV]] [[light]] and is used for applications that require transparency in this region. '''Large natural single crystals of quartz''' are pure silicon dioxide, and upon crushing are used for high quality specialty glasses. Synthetic amorphous silica, an almost 100&nbsp;% pure form of quartz, is the raw material for the most expensive specialty glasses, such as [[optical fiber]] core. [[Submarine communications cable|Undersea cables]] have sections doped with [[erbium]], which [[Fiber amplifier|amplify]] transmitted signals by [[laser]] emission from within the glass itself. Amorphous SiO<sub>2</sub> is also used as a [[dielectric]] material in [[integrated circuit]]s due to the smooth and electrically neutral interface it forms with [[silicon]].

[[Optical instrument]]s such as [[glasses]], [[camera|cameras]], [[Optical microscope|microscopes]], [[Optical telescope|telescopes]], and [[planetarium|planetaria]] are based on glass [[Lens (optics)|lenses]], [[mirror]]s, and [[Prism (optics)|prisms]]. The glasses used for making these instruments are categorized using a six-digit [[glass code]], or alternatively a letter-number code from the [[Schott Glass]] catalogue. For example, ''BK7'' is a low-[[dispersion (optics)|dispersion]] [[borosilicate glass|borosilicate]] [[crown glass (optics)|crown glass]], and ''SF10'' is a high-dispersion dense [[flint glass]]. The glasses are arranged by composition, refractive index, and [[Abbe number]].

Glass [[polymerization]] is a technique that can be used to incorporate additives that modify the properties of glass that would otherwise be destroyed during high temperature preparation. [[Sol gel]] is an example of glass polymerization and enables embedding of organic and bioactive molecules, to add a new level of functionality to glass.<ref>[http://www.solgel.com/biz/featcom/solgel.asp Sol-Gel Technologies Ltd.]</ref>

==Glass production==
{{main|Glass production|Float glass}}

===Glass production history===

Glass melting technology has passed through several stages:<ref name=ullmann>B. H. W. S. de Jong, "Glass"; in "Ullmann's Encyclopedia of Industrial Chemistry"; 5th edition, vol. A12, VCH Publishers, Weinheim, Germany, 1989, ISBN 3-527-20112-5, p 365-432.</ref>

* Glass was manufactured in open pits, ca. 3000 B.C. until the invention of the blowpipe in ca. 250 B.C.

* The mobile wood-fired melting pot furnace was used until around the 17th century by traveling glass manufacturers.

* Around 1688, a process for [[casting]] glass was developed, which led to glass becoming a much more commonly used material.{{Fact|date=December 2007}}

* The local pot furnace, fired by wood and coal was used between 1600 and 1850.

* The [[Cylinder blown sheet|cylinder method]] of creating [[flat glass]] was used in the [[United States of America]] for the first time in the 1820s. It was used to commercially produce windows.{{Fact|date=December 2007}}

* The invention of the glass pressing machine in 1827 allowed the mass production of inexpensive glass products.{{Fact|date=December 2007}}

* The gas-heated melting pot and tank furnaces dating from 1860, followed by the electric furnace of 1910.

* Hand-blown [[sheet glass]] was replaced in the 20th century by rolled plate glass.{{Fact|date=December 2007}}

* The [[float glass]] process was invented in the 1950s.

===Glass ingredients===
[[Image:Piasek_kwarcowy.jpg|thumb|right|[[Sand|Quartz sand]] (silica) as main raw material for commercial glass production]]

Pure [[silica]] (SiO<sub>2</sub>) has a "glass melting point"&mdash; at a [[viscosity]] of 10&nbsp;[[Pascal second|Pa·s]] (100&nbsp;[[Poise|P]])&mdash; of over 2300&nbsp;[[Celsius|°C]] (4200&nbsp;[[Fahrenheit|°F]]). While pure silica can be made into glass for special applications (see [[fused quartz]]), other substances are added to common glass to simplify processing. One is [[sodium carbonate]] (Na<sub>2</sub>CO<sub>3</sub>), which lowers the melting point to about 1500&nbsp;°C (2700&nbsp;°F) in [[soda-lime glass]]; "[[soda]]" refers to the original source of sodium carbonate in the [[soda ash]] obtained from certain plants. However, the soda makes the glass water soluble, which is usually undesirable, so [[lime (mineral)|lime]] ([[calcium oxide]] (CaO), generally obtained from [[limestone]]), some magnesium oxide (MgO) and aluminium oxide are added to provide for a better chemical durability. The resulting glass contains about 70 to 74 percent silica by weight and is called a [[soda-lime glass]].<ref name=ullmann/> Soda-lime glasses account for about 90 percent of manufactured glass.

As well as soda and lime, most common glass has other ingredients added to change its properties. [[Lead]] glass, such as [[lead crystal]] or [[flint glass]], is more 'brilliant' because the increased [[refractive index]] causes noticeably more "sparkles", while [[boron]] may be added to change the thermal and electrical properties, as in [[Pyrex]]. Adding [[barium]] also increases the refractive index. [[Thorium oxide]] gives glass a high refractive index and low dispersion, and was formerly used in producing high-quality lenses, but due to its [[radioactivity]] has been replaced by [[lanthanum oxide]] in modern glasses. Large amounts of [[iron]] are used in glass that absorbs [[infrared]] energy, such as heat absorbing filters for movie projectors, while [[cerium(IV) oxide]] can be used for glass that absorbs [[UV]] wavelengths (biologically damaging ionizing radiation).

Besides the chemicals mentioned, in some furnaces recycled glass ("cullet") is added, originating from the same factory or other sources. Cullet leads to savings not only in the raw materials, but also in the energy consumption of the glass furnace. However, impurities in the cullet may lead to product and equipment failure. Fining agents such as [[sodium sulfate]], [[sodium chloride]], or [[Antimony trioxide|antimony oxide]] are added to reduce the bubble content in the glass.<ref name=ullmann/>

A further raw material used in the production of soda-lime and fiber glass is calumite, which is a glassy granular by-product of the iron making industry, containing mainly silica, calcium oxide, alumina, magnesium oxide (and traces of iron oxide).<ref>[http://www.calumite.co.uk/ Calumite Limited, United Kingdom]</ref>

For obtaining the desired glass composition, the correct raw material mixture (batch) must be determined by [[glass batch calculation]].

===Contemporary glass production===

Following the [[glass batch]] preparation and mixing the raw materials are transported to the furnace. [[Soda-lime glass]] for mass production is melted in [[Glass_production#Furnace|gas fired units]]. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces and day tanks.<ref name=ullmann/>

After melting, homogenization and refining (removal of bubbles) the glass is [[Template:Glass forming|formed]]. Flat glass for windows and similar applications is formed by the [[float glass]] process, developed between 1953 and 1957 by Sir [[Alastair Pilkington]] and Kenneth Bickerstaff of the UK's Pilkington Brothers, which created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity.
Container glass for common bottles and jars is formed by [[Glass_container_production#Forming_process|blowing and pressing]] methods. Further glass forming techniques are summarized in the table [[Template:Glass forming|Glass forming techniques]].

Once the desired form is obtained, glass is usually [[Annealing (glass)|annealed]] for the removal of stresses.

Various surface treatment techniques, coatings, or [[lamination]] may follow to improve the chemical durability ([[Glass_production#Coatings|glass container coatings]], [[Glass_production#Internal_treatment|glass container internal treatment]]), strength ([[toughened glass]], [[bulletproof glass]], [[windshield]]s), or optical properties ([[insulated glazing]], [[anti-reflective coating]]).

===Glassmaking in the laboratory===

[[Image:Vitrification1.jpg|thumb|left|A vitrification experiment for the study of [[nuclear waste]] disposal at [[Pacific Northwest National Laboratory]].]]

[[Image:Failedmeltingtest.jpg|thumb|right|Failed laboratory glass melting test. The striations must be avoided through good [[homogenization]].]]

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale [[laboratory]] experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure [[chemicals]] are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as [[Alkali metal|alkali]] oxides and hydroxides, [[Alkaline earth metal|alkaline earth]] oxides and hydroxides, or [[boron oxide]]), or that the impurities are quantified (loss on ignition).<ref name=pnnl>[http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html Glass melting, Pacific Northwest National Laboratory]</ref> Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating [[Selenium dioxide|SeO<sub>2</sub>]]. Also, more readily reacting raw materials may be preferred over relatively [[inert]] ones, such as [[Aluminium hydroxide|Al(OH) <sub>3</sub>]] over [[Aluminium oxide|Al<sub>2</sub>O<sub>3</sub>]]. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass [[homogenization|homogeneity]] is achieved by homogenizing the raw materials mixture ([[glass batch]]), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually [[Annealing (glass)|annealed]] to prevent breakage during processing.<ref name=pnnl/><ref>[http://glassproperties.com/melting/ Glass melting in the laboratory]</ref>

See also: [[Optical_lens_design#Process|Optical lens design]], [[Fabrication and testing of optical components]]

==Silica-free glasses==
Besides common [[silica]]-based glasses, many other [[inorganic]] and [[Organic chemistry|organic]] materials may also form glasses, including [[plastics]] (e.g., [[acrylic glass]]), [[carbon]], [[Metallic glass|metals]], carbon dioxide (see below), [[phosphate]]s, [[borate]]s, [[chalcogenide glass|chalcogenides]], [[fluoride]]s, germanates (glasses based on [[Germanium oxide|GeO<sub>2</sub>]]), tellurites (glasses based on TeO<sub>2</sub>), antimonates (glasses based on Sb<sub>2</sub>O<sub>3</sub>), arsenates (glasses based on As<sub>2</sub>O<sub>3</sub>), titanates (glasses based on TiO<sub>2</sub>), tantalates (glasses based on Ta<sub>2</sub>O<sub>5</sub>), [[nitrate]]s, [[carbonate]]s and many other substances.<ref name=vogel/>

Some glasses that do not include silica as a major constituent may have physico-chemical properties useful for their application in [[fiber optics|fibre optics]] and other specialized technical applications. These include fluorozirconate, fluoroaluminate, [[aluminosilicate]], [[phosphate]] and [[chalcogenide glass]]es.

Under extremes of pressure and temperature solids may exhibit large structural and physical changes which can lead to [[polyamorphism|polyamorphic]] phase transitions.<ref>McMillan, P.F. Journal of Materials Chemistry, '''14''', 1506-1512 (2004)</ref> In 2006 Italian scientists created an amorphous phase of [[carbon dioxide]] using extreme pressure. The substance was named [[amorphous carbonia]](a-CO<sub>2</sub>) and exhibits an atomic structure resembling that of Silica.<ref>[http://www.newscientisttech.com/article.ns?id=dn9339 carbon dioxide glass created in the lab] 15 June 2006, www.newscientisttech.com. Retrieved 3 August 2006</ref>

==The physics of glass==
[[Image:Silica.jpg|thumbnail|right|The amorphous structure of glassy Silica (SiO<sub>2</sub>). No long range order is present, however there is local ordering with respect to the [[tetrahedral]] arrangement of Oxygen (O) atoms around the Silicon (Si) atoms.]]

The standard definition of a glass (or [[vitreous]] solid) requires the solid phase to be formed by rapid melt quenching.<ref name=Zallen83/><ref name=Cusack87/><ref name=Elliot84/> Glass is therefore formed via a [[supercooled]] liquid and cooled sufficiently rapidly (relative to the characteristic [[crystallisation]] time) from its molten state through its [[glass transition temperature]], T<sub>g</sub>, that the supercooled disordered atomic configuration at T<sub>g</sub>, is frozen into the solid state. Generally, the structure of a glass exists in a [[metastability in molecules|metastable]] state with respect to its [[crystalline]] form, although in certain circumstances, for example in [[atactic]] polymers, there is no crystalline analogue of the amorphous phase <ref name=Folmer>"Folmer, J. C. W.; Franzen, Stefan." Study of polymer glasses by modulated differential scanning calorimetry in the undergraduate physical chemistry laboratory. Journal of Chemical Education (2003), 80(7), 813-818. CODEN: JCEDA8 ISSN:0021-9584. </ref>. By definition as an [[amorphous solid]], the atomic structure of a glass lacks any long range [[translational symmetry|translational periodicity]]. However, by virtue of the local [[chemical bonding]] constraints glasses do possess a high degree of short-range order with respect to local atomic [[polyhedra]]<ref>Salmon, P.S., ''Order within disorder'', Nature Materials, '''1'''(87), (2002)</ref>. It is deemed that the bonding structure of glasses, although disordered, has the same symmetry signature ([[Hausdorff dimension|Hausdorff-Besicovitch dimensionality]]) as for crystalline materials<ref>M.I. Ojovan, W.E. Lee. Topologically disordered systems at the glass transition. ''J. Phys.: Condensed Matter'', '''18''', 11507-11520 (2006)</ref>.

===Glass versus a supercooled liquid===

Glass is generally treated as an [[amorphous solid]] rather than a liquid, though both views can be justified.<ref name=Gibbs>{{cite web| url = http://math.ucr.edu/home/baez/physics/General/Glass/glass.html| title = Is glass liquid or solid? | accessdate = 2007-03-21| author = Philip Gibbs}}</ref> However, the notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see [[viscosity of amorphous materials]]). From a more commonsense point of view, glass should be considered a solid since it is rigid according to everyday experience.<ref>"Philip Gibbs" ''Glass Worldwide'', (may/june 2007), pp 14-18</ref>

Some people believe glass is a liquid due to its lack of a first-order [[phase transition]] <ref name=Gibbs/><ref>{{cite web| url = http://www.jimloy.com/physics/glass.htm| title = Glass Is A Liquid? | accessdate = 2007-03-21| author = Jim Loy}}</ref> where certain [[thermodynamics|thermodynamic]] [[thermodynamic variable|variables]] such as [[volume]], [[entropy]] and [[enthalpy]] are continuous through the glass transition temperature. However, the glass transition temperature may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the [[thermal expansion|thermal expansivity]] and [[heat capacity]] are discontinuous. Despite this, thermodynamic phase transition theory does not entirely hold for glass, and hence the glass transition cannot be classed as a genuine thermodynamic phase transition.<ref name=Elliot84/>

Although the [[atom|atomic]] structure of glass shares characteristics of the structure in a [[supercooled liquid]], glass is generally classed as solid below its glass transition temperature.<ref>{{cite web| url = http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html| title = Glass: Liquid or Solid -- Science vs. an Urban Legend | accessdate = 2007-04-08| author = Florin Neumann}}</ref> There is also the problem that a supercooled liquid is still a liquid and not a solid but it is below the freezing point of the material and will crystallize almost instantly if a crystal is added as a [[core]]. The change in [[heat capacity]] at a [[glass transition]] and a [[melting point|melting transition]] of comparable materials are typically of the same order of magnitude indicating that the change in active [[degrees of freedom]] is comparable as well. Both in a glass and in a crystal it is mostly only the [[vibration|vibrational]] degrees of freedom that remain active, whereas [[rotational]] and [[translation (physics)|translational]] motion becomes impossible explaining why glasses and crystalline materials are hard.

===Behavior of antique glass===

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, which is a property of liquid. The likely source of this unfounded belief is that when panes of glass were commonly made by [[glassblowing|glassblowers]], the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the [[Crown glass (window)|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 [[centripetal force]] relaxation. When actually installed in a window frame, the glass would be placed thicker side down for the sake of stability and visual sparkle.<ref>[http://www.abc.net.au/science/k2/homework/s95602.htm Dr Karl's Homework: Glass Flows]</ref> Occasionally such glass has been found thinner side down or on either side of the window's edge, as would be caused by carelessness at the time of installation.

Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness. Modern glass intended for windows is produced as [[float glass]] and is very uniform in thickness.

Several other points exemplify the misconception of the 'cathedral glass' theory:

* Writing in the [[American Journal of Physics]],<ref>"Do Cathedral Glasses Flow?" ''Am. J. Phys.'', '''66''' (May 1998), pp 392&ndash;396</ref> physicist [[Edgar D. Zanotto]] states "...the predicted [[relaxation time]] for GeO<sub>2</sub> at room temperature is 10<sup>32</sup> years. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer".
* If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more &mdash; but this is not observed. Similarly, prehistoric [[obsidian]] blades should have lost their edge; this is not observed either (although obsidian may have a different viscosity from window glass).<ref name=Gibbs/>
* If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes. Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed.<ref name=Gibbs/>
* There are many examples of centuries old glass shelving which has not bent, even though it is under much higher stress from gravitational loads than vertical window glass.

Some glasses have a glass transition temperature close to or below room temperature. The behaviour of a material that has a glass transition close to room temperature depends upon the timescale during which the material is manipulated. If the material is hit it may break like a solid glass, however if the material is left on a table for a week it may flow like a liquid. This simply means that for the fast timescale its transition temperature is above room temperature, but for the slow one it is below. The shift in temperature with timescale is not very large however as indicated by the transition of polypropylene glycol of -72 °C and -71 °C over different timescales. <ref name=Folmer/> To observe window glass flowing as liquid at room temperature we would have to wait a much longer time than the universe exists. Therefore it is safe to consider a glass a solid far enough below its transition temperature: Cathedral glass does not flow because its glass transition temperature is many hundreds of degrees above room temperature. Close to this temperature there are interesting time-dependent properties. One of these is known as aging. Many polymers that we use in daily life such as [[rubber]], [[polystyrene]] and [[polypropylene]] are in a glassy state but they are not too far below their glass transition temperature. Their mechanical properties may well change over time and this is serious concern when applying these materials in construction.

===Physical properties===

The following table lists some physical properties of common glasses. Unless otherwise stated, the technical glass compositions and many experimentally determined properties are taken from one large study.<ref name=seward>"High temperature glass melt property database for process modeling"; Eds.: Thomas P. Seward III and Terese Vascott; The American Ceramic Society, Westerville, Ohio, 2005, ISBN 1-57498-225-7</ref> Unless stated otherwise, the properties of [[fused silica]] (quartz glass) and [[germanium oxide|germania]] glass are derived from the SciGlass [[glass database]] by forming the [[arithmetic mean]] of all the experimental values from different authors (in general more than 10 independent sources for quartz glass and Tg of germanium oxide glass). Those values marked in ''italic'' font have been interpolated from sililar glass compositions (see [[Calculation of glass properties]]) due to the lack of experimental data.

{| class="wikitable"
|-
! Properties
! [[Soda-lime glass]] (for [[Container glass|containers]])<ref>Soda-lime glass for containers is slightly different from soda-lime glass for windows (also called flat glass or [[float glass]]). Float glass has a higher [[magnesium oxide]] content as compared to container glass, and a lower silica and [[calcium oxide]] content. For further details see main article [[Soda-lime glass]].</ref>
! [[Borosilicate]] (low expansion, similar to [[Pyrex]], [[Borosilicate glass|Duran]])
! Glass wool (for [[thermal insulation]])
! Special [[Optics|optical]] glass (similar to<br>[[Lead crystal]])
! [[Fused silica]]
! [[germanium oxide|Germania]] glass
! Germanium selenide glass
|-
| Chemical<br>composition,<br>wt%
| 74 [[Silicon dioxide|SiO<sub>2</sub>]], 13 [[Sodium oxide|Na<sub>2</sub>O]], 10.5 [[Calcium oxide|CaO]], 1.3 [[Aluminium oxide|Al<sub>2</sub>O<sub>3</sub>]], 0.3 [[Potassium oxide|K<sub>2</sub>O]], 0.2 [[Sulfur trioxide|SO<sub>3</sub>]], 0.2 [[Magnesium oxide|MgO]], 0.01 [[Titanium dioxide|TiO<sub>2</sub>]], 0.04 [[Iron(III) oxide|Fe<sub>2</sub>O<sub>3</sub>]]
| 81 SiO<sub>2</sub>, 12.5 [[Boron trioxide|B<sub>2</sub>O<sub>3</sub>]], 4 Na<sub>2</sub>O, 2.2 Al<sub>2</sub>O<sub>3</sub>, 0.02 CaO, 0.06 K<sub>2</sub>O
| 63 SiO<sub>2</sub>, 16 Na<sub>2</sub>O, 8 CaO, 3.3 B<sub>2</sub>O<sub>3</sub>, 5 Al<sub>2</sub>O<sub>3</sub>, 3.5 MgO, 0.8 K<sub>2</sub>O, 0.3 Fe<sub>2</sub>O<sub>3</sub>, 0.2 SO<sub>3</sub>
| 41.2 SiO<sub>2</sub>, 34.1 [[Lead oxide|PbO]], 12.4 [[Barium oxide|BaO]], 6.3 [[Zinc oxide|ZnO]], 3.0 K<sub>2</sub>O, 2.5 CaO, 0.35 [[Antimony trioxide|Sb<sub>2</sub>O<sub>3</sub>]], 0.2 [[Arsenic trioxide|As<sub>2</sub>O<sub>3</sub>]]
| SiO<sub>2</sub>
| GeO<sub>2</sub>
| GeSe<sub>2</sub>
|-
| [[Viscosity]]<br>log(η, Pa·s) = A +<br>B / (T in °C - T<sub>o</sub>)
| 550-1450°C:<br>A = -2.309<br>B = 3922<br>T<sub>o</sub> = 291
| 550-1450°C:<br>A = -2.834<br>B = 6668<br>T<sub>o</sub> = 108
| 550-1400°C:<br>A = -2.323<br>B = 3232<br>T<sub>o</sub> = 318
| 500-690°C:<br>A = -35.59<br>B = 60930<br>T<sub>o</sub> = -741
| 1140-2320°C:<br>A = -7.766<br>B = 27913<br>T<sub>o</sub> = -271.7
| 515-1540°C:<br>A = -11.044<br>B = 30979<br>T<sub>o</sub> = -837
|-
| [[Glass transition temperature|Glass transition]]<br>[[Glass transition temperature|temperature]], T<sub>g</sub>, °C
| 573
| 536
| 551
| ~540
| 1140
| 526 ± 27<ref>Leadbetter et al, Journal of non-crystalline solids, 7:37-52 (1972)</ref><ref>Micoulaut et al, Physical Review E, 73:031504 (2006)</ref><ref>35 T<sub>g</sub> data for GeO<sub>2</sub> from [[Sciglass|SciGlass]] 6.7</ref>
| 395 <ref name=Kotkata94>Kotkata et al., J. Phys. D: Appl. Phys. '''27''' pp 623-627 (1994)</ref>
|-
| [[Coefficient of thermal expansion|Coefficient of]]<br>[[Coefficient of thermal expansion|thermal expansion]],<br>ppm/K, ~100-300°C
| 9
| 3.5
| 10
| 7
| 0.55
| 7.3
|
|-
| [[Density]]<br>at 20°C, g/cm<sup>3</sup>
| 2.52
| 2.235
| 2.550
| 3.86
| 2.203
| 3.65 <ref>Salmon et al, Physical Review Letters, '''96''', 235502 (2006)</ref>
| 4.16 <ref name=Kotkata94/>
|-
| [[Refractive index]] n<sub>D</sub><ref name=refind>The subscript ''D'' indicates that the refractive index ''n'' was measured at a wavelength λ of 589.29 nm, ''F'' and ''C'' indicate 486.13 nm (blue) and 656.27 nm (red) respectively (see article [[Fraunhofer lines]])</ref> at 20°C
| ''1.518''
| 1.473
| 1.531
| 1.650
| 1.459
| 1.608
|
|-
| [[Dispersion (optics)|Dispersion]] at 20°C,<br>10<sup>4</sup>&times;(n<sub>F</sub>-n<sub>C</sub>)<ref name=refind/>
| ''86.7''
| ''72.3''
| ''89.5''
| 169
| 67.8
| 146
|
|-
| [[Young's modulus]]<br>at 20°C, GPa
| ''72''
| ''65''
| ''75''
| 67
| 72
| 43.3 <ref>Hwa et al, Materials Chemistry and Physics, '''94''', 1, 37-41 (2005)</ref>
|
|-
| [[Shear modulus]]<br>at 20°C, GPa
| ''29.8''
| ''28.2''
|
| 26.8
| 31.3
|
|
|-
| [[Liquidus temperature|Liquidus]]<br>[[Liquidus temperature|temperature]], °C
| ''1040''
| 1070<ref>Valid for glass composition, wt%: 80.7 SiO<sub>2</sub>, 13.1 B<sub>2</sub>O<sub>3</sub>, 4.1 Na<sub>2</sub>O, 2.1 Al<sub>2</sub>O<sub>3</sub>; Reference: Baak N. T. E. A. and Rapp C. F., GB Patent No. 1132885 Cl C 03 C 3/04, Abridg. Specif., 1968; Assignee: Owens-Illinois, Inc. (US).</ref>
|
|
| 1715
| 1115
|
|-
| [[Heat capacity|Heat]]<br>[[Heat capacity|capacity]] at 20°C,<br>J/(mol·K)
| ''49''
| ''50''
| ''50''
| 51
| 44
| 52
|
|-
| [[Surface tension]],<br>at ~1300°C, mJ/m<sup>2</sup>
| 315
| 370
| 290
|
|
|
|
|-
| [[Chemical durability]],<br>[[Corrosion#Glass_corrosion_tests|Hydrolytic class]],<br>after ISO 719<ref>[http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=4948 International Organization for Standardization, Procedure 719 (1985)]</ref>
| ''3''
| ''1''
| ''3''
|
|
|
|
|}

====Color====
[[Image:Green color of float glass.jpg|thumb|right|Common soda-lime [[float glass]] appears green in thick sections because of Fe<sup>2+</sup> impurities.]]
{{main|Glass_production#Colors}}

[[Color]]s in glass may be obtained by addition of coloring ions that are homogeneously distributed and by precipitation of finely dispersed particles (such as in [[Photochromic lens|photochromic glasses]]).<ref name=vogel/> Ordinary [[soda-lime glass]] appears colorless to the naked eye when it is thin, although [[iron(II) oxide]] (FeO) impurities of up to 0.1 wt%<ref name=seward/> produce a [[green]] tint which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and [[Chromium(III) oxide|Cr<sub>2</sub>O<sub>3</sub>]] additions may be used for the production of green bottles. [[Sulfur]], together with [[carbon]] and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black.<ref>[http://1st.glassman.com/articles/glasscolouring.html Substances Used in the Making of Coloured Glass] 1st.glassman.com (David M Issitt). Retrieved 3 August 2006</ref> [[Manganese dioxide]] can be added in small amounts to remove the green tint given by iron(II) oxide.

== History ==
[[Image:Roman diatretglas.jpg|thumb|right|Roman [[Cage cup| Cage Cup]] from the 4th century A.D.]]
[[Image:2006 0814RomanGlassHistriaMuseum20060336.jpg|thumb|right|Roman glass]]
:''see also category [[:Category:Glass history|Glass history]]''
Naturally occurring glass, especially [[obsidian]], has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. According to [[Pliny the Elder]], [[Phoenician]] traders were the first to stumble upon glass manufacturing techniques at the site of the [[Belus River]]. Agricola, ''[[De re metallica]]'', reported a traditional serendipitous "discovery" tale of familiar type:

<blockquote>"The tradition is that a merchant ship laden with [[Nitre|nitrum]] being moored at this place, the merchants were preparing their meal on the beach, and not having stones to prop up their pots, they used lumps of nitrum from the ship, which fused and mixed with the sands of the shore, and there flowed streams of a new translucent liquid, and thus was the origin of glass."<ref name=Agricola>[[Agricola]], Georgius, ''[[De re metallica]]'', translated by Herbert Clark Hoover and Lou Henry Hoover, Dover Publishing. [http://www.farlang.com/gemstones/agricola-metallica/page_001 De Re Metallica Trans. by Hoover Online Version] [http://www.farlang.com/gemstones/agricola-metallica/page_621 Page 586] Retrieved = 12 September 2007 </ref></blockquote>

This account is more a reflection of Roman experience of glass production, however, as white silica sand from this area was used in the production of Roman glass due to its low impurity levels. But in general archaeological evidence suggests that the first true glass was made in coastal north Syria, [[Mesopotamia]] or [[Old Kingdom|Old Kingdom Egypt]].<ref>{{cite web| url = http://www.glassonline.com/infoserv/history.html| title = Glass Online: The History of Glass| accessdate = 2007-10-29}}</ref> Due to Egypt's favourable environment for preservation, the majority of well-studied early glass is found in Egypt, although some of this is likely to have been imported. The earliest known glass objects, of the mid third millennium BC, were beads, perhaps initially created as accidental by-products of metal-working [[slag]]s or during the production of [[faience]], a pre-glass [[vitreous]] material made by a process similar to glazing.<ref>True glazing over a ceramic body was not used until many centuries after the production of the first glass.</ref>

During the [[Late Bronze Age]] in [[Egypt]] and [[Western Asia]] there was an explosion in glass-making technology. Archaeological finds from this period include coloured glass [[ingots]], vessels (often coloured and shaped in imitation of highly prized wares of semi-precious stones) and the ubiquitous beads. The alkali of Syrian and Egyptian glass was [[soda ash]], sodium carbonate, which can be extracted from the ashes of many plants, notably [[halophile]] seashore plants: (see [[saltwort]]). The earliest vessels were 'core-wound', produced by winding a ductile rope of metal round a shaped core of sand and clay over a metal rod, then fusing it with repeated reheatings. Threads of thin glass of different colours made with admixtures of oxides were subsequently wound around these to create patterns, which could be drawn into festoons with a metal raking tools. The vessel would then be rolled flat ('marvered') on a slab in order to press the decorative threads into its body. Handles and feet were applied separately. The rod was subsequently allowed to cool as the glass slowly [[Annealing|annealed]] and was eventually removed from the centre of the vessel, after which the core material was scraped out. Glass shapes for [[inlay]]s were also often created in moulds. Much early glass production, however, relied on grinding techniques borrowed from stone working. This meant that the glass was ground and carved in a cold state.
By the 15th century BC extensive glass production was occurring in [[Western Asia]] and [[Egypt]]. It is thought the techniques and recipes required for the initial fusing of glass from raw materials was a closely guarded technological secret reserved for the large palace industries of powerful states. Glass workers in other areas therefore relied on imports of pre-formed glass, often in the form of cast ingots such as those found on the [[Ulu Burun]] shipwreck off the coast of Turkey.

Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilisations seem to have brought glass-making to a halt. It picked up again in its former sites, in Syria and Cyprus, in the ninth century BC, when the techniques for making colourless glass were discovered. In Egypt glass-making did not revive until it was reintroduced in [[Ptolemaic Egypt|Ptolemaic Alexandria]]. Core-formed vessels and beads were still widely produced, but other techniques came to the fore with experimentation and technological advancements. During the [[Hellenistic]] period many new techniques of glass production were introduced and glass began to be used to make larger pieces, notably table wares. Techniques developed during this period include 'slumping' [[viscous]] (but not fully molten) glass over a mould in order to form a dish and '[[millefiori]]' (meaning 'thousand flowers') technique, where canes of multi-coloured glass were sliced and the slices arranged together and fused in a mould to create a mosaic-like effect. It was also during this period that colourless or decoloured glass began to be prized and methods for achieving this effect were investigated more fully.
During the first century BC [[glass blowing]] was discovered on the Syro-Palestinian coast, revolutionising the industry and laying the way for the explosion of glass production that occurred throughout the Roman world. Over the next 1000 years glass making and working continued and spread through southern Europe and beyond.

===Romans===

A full discussion of Roman glass making and working can be found on the [[Roman glass]] page.

===Anglo-Saxon world===

Evidence for glass making, working and use in the 5th to 8th centuries in England is discussed in the [[Anglo-Saxon glass]] page.

===Islamic world===

In the [[Islamic Golden Age|medieval Islamic world]], the first clear, colourless, high-purity glasses were produced by [[Alchemy (Islam)|Muslim chemists]], [[Islamic architecture|architects]] and [[Inventions in the Muslim world|engineers]] in the 9th century. Examples include [[Silica glass]] and colourless high-purity glass invented by [[Abbas Ibn Firnas]] (810-887), who was the first to produce glass from [[sand]] and [[Rock (geology)|stones]].<ref name=White-100>[[Lynn Townsend White, Jr.]] (Spring, 1961). "Eilmer of Malmesbury, an Eleventh Century Aviator: A Case Study of Technological Innovation, Its Context and Tradition", ''Technology and Culture'' '''2''' (2), pp. 97-111 [100].
{{quote|"Ibn Firnas was a [[polymath]]: a [[Islamic medicine|physician]], a rather bad [[Islamic poetry|poet]], the first to make glass from [[Rock (geology)|stones]], a student of [[Islamic music|music]], and inventor of some sort of [[metronome]]."}}</ref> The [[Arabic poetry|Arab poet]] al-[[Buhturi]] (820-897) described the clarity of such glass,
"Its colour hides the glass as if it is standing in it without a container."<ref name=Glass>[[Ahmad Y Hassan]], [http://www.history-science-technology.com/Articles/articles%2093.htm Assessment of ''Kitab al-Durra al-Maknuna''], ''History of Science and Technology in Islam''.</ref>

[[Stained glass]] was also first produced by [[Islamic architecture|Muslim architects]] in [[Southwest Asia]] using coloured glass rather than stone. In the 8th century, the [[Arab]] chemist [[Geber|Jabir ibn Hayyan]] (Geber) scientifically described 46 original recipes for producing coloured glass in ''Kitab al-Durra al-Maknuna'' (''The Book of the Hidden Pearl''), in addition to 12 recipes inserted by al-Marrakishi in a later edition of the book.<ref>[[Ahmad Y Hassan]], [http://www.history-science-technology.com/Articles/articles%209.htm The Manufacture of Coloured Glass], ''History of Science and Technology in Islam''.</ref>

The [[parabolic mirror]] was first described by [[Ibn Sahl]] in his ''On the Burning Instruments'' in the 10th century, and later described again in [[Ibn al-Haytham]]'s ''On Burning Mirrors'' and ''[[Book of Optics]]'' (1021).<ref>Roshdi Rashed (1990), "A Pioneer in Anaclastics: Ibn Sahl on Burning Mirrors and Lenses", ''[[Isis (journal)|Isis]]'' '''81''' (3), p. 464-491 [464-468].</ref> By the 11th century, clear glass [[mirror]]s were being produced in [[Al-Andalus|Islamic Spain]]. The first glass [[factories]] were also built by Muslim craftsmen in the Islamic world. The first glass factories in [[Christian]] Europe were later built in the 11th century by Muslim [[Egypt]]ian craftsmen in [[Corinth]], [[Greece]].<ref>[[Ahmad Y Hassan]], [http://www.history-science-technology.com/Articles/articles%2072.htm Transfer Of Islamic Technology To The West, Part III: Technology Transfer in the Chemical Industries], ''History of Science and Technology in Islam''.</ref>

===Medieval Europe===
[[Image:AndelysVitrail.jpg|thumb|left|A 16th-century [[stained glass]] window]]

Glass objects from the 7th and 8th centuries have been found on the island of [[Torcello]] near [[Venice]]. These form an important link between Roman times and the later importance of that city in the production of the material. Around 1000&nbsp;AD, an important technical breakthrough was made in Northern Europe when soda glass, produced from white pebbles and burnt vegetation was replaced by glass made from a much more readily available material: [[potash]] obtained from wood ashes. From this point on, northern glass differed significantly from that made in the Mediterranean area, where soda remained in common use.<ref>{{cite web| url = http://nautarch.tamu.edu/class/anth605/File5.htm| title = Glass Conservation | accessdate = 2007-03-21| author = Donny L. Hamilton | publisher = Conservation Research Laboratory, Texas A&M University}}</ref>

Until the 12th century, [[stained glass]] -- glass to which metallic or other impurities had been added for coloring -- was not widely used.

The 11th century saw the emergence in [[Germany]] of new ways of making sheet glass by blowing spheres. The spheres were swung out to form cylinders and then cut while still hot, after which the sheets were flattened. This technique was perfected in 13th century [[Venice]].

The [[Crown glass process]] was used up to the mid-19th century. In this process, the [[glassblower]] would spin approximately 9 [[Avoirdupois|pounds]] (4&nbsp;kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 [[foot (unit of length)|feet]] (1.5&nbsp;[[metre|m]]) in diameter. The disk would then be cut into panes.

===Late medieval Northern Europe===

Glass making in late medieval Northern Europe is discussed in the article on [[Forest glass]].

=== Murano glassmaking ===
{{main|Murano glass|Venetian Glass}}

The center for glassmaking from the 14th century was the island of [[Murano]], which developed many new techniques and became the center of a lucrative export trade in [[dinnerware]], [[mirror]]s, and other luxury items. What made Venetian [[Murano glass]] significantly different was that the local quartz pebbles were almost pure [[silica]], and were ground into a fine clear sand that was combined with [[soda ash]] obtained from the [[Levant]], for which the Venetians held the sole [[monopoly]]. The clearest and finest glass is tinted in two ways: firstly, a small or large amount of a natural coloring agent is ground and melted with the glass. Many of these coloring agents still exist today; for a list of coloring agents, see below. Black glass was called '''obsidianus''' after [[obsidian]] stone. A second method is apparently to produce a black glass which, when held to the light, will show the true color that this glass will give to another glass when used as a dye. <ref name=Agricola1>[[Georg Agricola]]''[[De Natura Fossilium]]'', Textbook of Mineralogy, M.C. Bandy, J. Bandy, Mineralogical Society of America, 1955, Page 111 [http://www.farlang.com/gemstones/agricola-metallica/page_001 Section on Murano Glass, De Natura Fossilium] Retrieved 12 September 2007 </ref>

The Venetian ability to produce this superior form of glass resulted in a trade advantage over other glass producing lands. [[Murano]]’s reputation as a center for glassmaking was born when the Venetian Republic, fearing fire might burn down the city’s mostly wood buildings, ordered glassmakers to move their foundries to Murano in 1291. Murano's glassmakers were soon the island’s most prominent citizens. Glassmakers were not allowed to leave the Republic. Many took a risk and set up glass furnaces in surrounding cities and as far afield as England and the Netherlands.

== Glass art ==

{{main|Glass art}}

[[Image:Glass worker, Reijmyre glasbruk, Sweden.jpg|thumb|right|A [[vase]] being created at the [[Kosta Glasbruk|Reijmyre glassworks]], [[Sweden]]]]

[[Image:Paperweight, Corning Museum of Glass.jpg|thumb|[[Paperweight]] with items inside the glass, [[Corning Museum of Glass]]]]

Beginning in the late 20th century, glass started to become highly collectible as art. Works of art in glass can be seen in a variety of museums, including the Chrysler Museum, the Museum of Glass in Tacoma, the Metropolitan Museum of Art, the Toledo Museum of Art, and [[Corning Museum of Glass]], in [[Corning, NY]], which houses the world's largest collection of glass art and history, with more than 45,000 objects in its collection.<ref name=Corning>{{cite web |title= Corning Museum of Glass|url=http://www.cmog.org/index.asp?pageId=1276|accessdate=2007-10-14|format= }}</ref>

Several of the most common techniques for producing glass art include: [[glass blowing|blowing]], kiln-casting, fusing, slumping, pate-de-verre, flame-working, hot-sculpting and cold-working. Cold work includes traditional [[stained glass]] work as well as other methods of shaping glass at room temperature. Glass can also be cut with a diamond saw, or copper wheels embedded with abrasives, and polished to give gleaming facets; the technique used in creating [[waterford crystal]] <ref>{{cite web |title=Waterford Crystal Vistors Centre|url=http://www.waterfordvisitorcentre.com/|accessdate=2007-10-19|format= }}</ref>. Art is sometimes etched into glass via the use of acid, caustic, or abrasive substances. Traditionally this was done after the glass was blown or cast. In the 1920s a new mould-etch process was invented, in which art was etched directly into the mould, so that each cast piece emerged from the mould with the image already on the surface of the glass. This reduced manufacturing costs and, combined with a wider use of colored glass, led to cheap glassware in the 1930s, which later became known as Depression glass<ref>{{cite web |title=Depression Glass|url=http://www.glassonweb.com/articles/article/201/|accessdate=2007-10-19|format= }}</ref>. As the types of acids used in this process are extremely hazardous, abrasive methods have gained popularity.

Objects made out of glass include not only traditional objects such as vessels ([[bowl]]s, [[vase]]s, [[bottle]]s, and other containers), [[Paperweight collecting|paperweights]], [[marbles]], [[bead]]s, but an endless range of [[sculpture]] and installation art as well. Colored glass is often used, though sometimes the glass is painted, innumerable examples exist of the use of [[stained glass]].

The [[Harvard Museum of Natural History]] has a collection of extremely detailed models of flowers made of painted glass. These were [[lampworking|lampworked]] by [[Leopold Blaschka]] and his son Rudolph, who never revealed the method he used to make them. The Blaschka [[Glass Flowers]] are still an inspiration to glassblowers today. <ref> [http://www.hmnh.harvard.edu/exhibitions/glassflowers.html the Harvard Museum of Natural History's page on the exhibit] </ref>

== See also ==
* [[Aluminium oxynitride]]
* [[Favrile iridescent glass]]
* [[Template:List of glass companies|Glass makers and brands]]
* [[Glass recycling]]
* [[Glass fibre]]
* [[Magnifying glass]]
* [[Opaline glass]]

== References ==

{{reflist|2}}

== Bibliography ==

* Noel C. Stokes; ''The Glass and Glazing Handbook''; [[Standards Australia]]; SAA HB125–1998
* Brugmann, Birte. ''Glass Beads from Anglo-Saxon Graves: A Study on the Provenance and Chronology of Glass Beads from Anglo-Saxon Graves, Based on Visual Examination''. Oxbow Books, 2004. ISBN 1-84217-104-6

==External links==
{{wiktionary}}
{{commonscat}}

* [http://www.20thcenturyglass.com/glass_encyclopedia_home.htm Glass Encyclopedia - A comprehensive guide to all types of antique and collectable glass, with information, pictures and references]
* [http://www.justglass-online.com/ Free information and articles about Designer Glassware, Vintage Art Glass, Depression Glass & Collectible Glass | JustGlass-Online.com]
* [http://www.civilisations.ca/hist/verre/veint01e.html The Canadian Museum of Civilization - The Story of Glass Making in Canada]
* [http://www.cmog.org/ Corning Museum of Glass]
* [http://www.worldartglass.com/index.asp A comprehensive guide to art glass and crystal around the world]
* [http://venixe.com/en/glass-working-descriptions/description-of-the-art-of-murano-glass-furnace-and-mol.html Working Description Furnace & Moleria - Murano Glass]
* [http://www.glassonweb.com Informative website about the glass industry]
* [http://1st.glassman.com/articles/glasscolouring.html Substances used in the Making of Colored Glass]
* [http://glassproperties.com/ Glass property measurement and calculation]
* [http://www.glassfacts.info Almost 400 articles and images about glass (mostly art glass)]

{{Glass science}}
{{Glass forming}}
{{List of glass companies}}

[[Category:Glass| ]]
[[Category:Glass art]]
[[Category:Glass history]]
[[Category:Dielectrics]]
[[Category:Recyclable materials]]
[[Category:Packaging materials]]
[[Category:Materials science]]

{{Link FA|af}}

[[af:Glas]]
[[ar:زجاج]]
[[be:Шкло]]
[[bs:Staklo]]
[[bg:Стъкло]]
[[ca:Vidre]]
[[cs:Sklo]]
[[cy:Gwydr]]
[[da:Glas]]
[[de:Glas]]
[[et:Klaas]]
[[el:Γυαλί]]
[[es:Vidrio]]
[[eo:Vitro]]
[[eu:Beira]]
[[fa:شیشه]]
[[fr:Verre]]
[[gl:Vidro]]
[[ko:유리]]
[[hr:Staklo]]
[[io:Vitro]]
[[id:Kaca]]
[[os:Авг]]
[[is:Gler]]
[[it:Vetro]]
[[he:זכוכית]]
[[jv:Kaca]]
[[ku:Cam]]
[[la:Vitrum]]
[[lv:Stikls]]
[[lt:Stiklas]]
[[lmo:Véder]]
[[hu:Üveg]]
[[mk:Стакло]]
[[mt:Ħġieġ]]
[[ms:Kaca]]
[[nl:Glas]]
[[ja:ガラス]]
[[nap:Vrito]]
[[no:Glass (materiale)]]
[[nn:Glas]]
[[oc:Veire]]
[[ug:ئەينەك]]
[[pl:Szkło]]
[[pt:Vidro]]
[[ro:Sticlă]]
[[qu:Q'ispillu]]
[[ru:Стекло]]
[[simple:Glass]]
[[sk:Sklo]]
[[sl:Steklo]]
[[sr:Стакло]]
[[sh:Staklo]]
[[fi:Lasi]]
[[sv:Glas]]
[[ta:கண்ணாடி]]
[[th:แก้ว]]
[[vi:Thủy tinh (chất)]]
[[tr:Cam]]
[[uk:Скло]]
[[vec:Véro]]
[[zh-yue:玻璃]]
[[zh:玻璃]]

Revision as of 19:57, 10 April 2008

i'VE TAKEN THE LIBERTY OF REMOVING THIS IRREVLEVANT BLOG. glass does not exist!

Retrieved from "https://en.wikipedia.org/w/index.php?title=Glass&oldid=204764208"