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'''Glass''' is a [[non-crystalline solid]] that is often [[transparency and translucency|transparent]], brittle and chemically inert. It has widespread practical, technological, and decorative use in, for example, [[window]] panes, [[tableware]], and [[optics]].

Glass is most often formed by rapid cooling ([[quenching]]) of the [[Melting|molten]] form; some glasses such as [[volcanic glass]] are naturally occurring. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound [[silicon dioxide|silica]] (silicon dioxide, or [[quartz]]), the primary constituent of [[sand]]. [[Soda–lime glass]], containing around 70% silica, accounts for around 90% of manufactured glass. The term ''glass'', in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and [[glasses|eyeglasses]], are so commonly made of silicate-based glass that they are simply called by the name of the material.

Despite being brittle, buried silicate glass will survive for very long periods if not disturbed, and many examples of glass fragments exist from early glassmaking cultures. Archaeological evidence suggests glassmaking dates back to at least 3,600 BC in [[Mesopotamia]], [[Egypt]], or [[Syria]]. The earliest known glass objects were [[beads]], perhaps created accidentally during [[metalworking]] or the production of [[faience]]. Due to its ease of [[formability]] into any shape, glass has been traditionally used for vessels, such as [[bowl (vessel)|bowls]], [[vase]]s, [[bottle]]s, jars and drinking glasses. In its most solid forms, it has also been used for [[paperweight collecting|paperweights]] and [[Marble (toy)|marbles]]. Glass can be coloured by adding metal salts or painted and printed with [[vitreous enamel]]s, leading to its use in [[stained glass]] windows and other [[glass art]] objects. The [[refraction|refractive]], [[Reflection (physics)|reflective]] and [[Transmission coefficient#Optics|transmission]] properties of glass make glass suitable for manufacturing [[Lens (optics)|optical lenses]], [[Prism (optics)|prism]]s, and [[optoelectronics]] materials. Extruded [[glass fiber|glass fibres]] have application as [[optical fiber|optical fibres]] in communications networks, thermal insulating material when matted as [[glass wool]] so as to trap air, or in glass-fibre reinforced plastic ([[fiberglass|fibreglass]]).

== Microscopic structure ==
The standard definition of a ''glass'' (or vitreous solid) is a solid formed by rapid melt [[quenching]].<ref>[[ASTM]] definition of glass from 1945</ref><ref name="Zallen83">{{cite book |last=Zallen |first=R. |title=The Physics of Amorphous Solids |publisher=John Wiley |place=New York |year=1983 |pages=1–32|isbn=978-0-471-01968-8}}</ref><ref name="Cusack87">{{Cite book |last=Cusack |first=N.E. |title=The physics of structurally disordered matter: an introduction |publisher=Adam Hilger in association with the University of Sussex press |year=1987 |page=13 |isbn=978-0-85274-829-9}}</ref><ref name="Horst Scholze 1991">{{Cite book |last=Scholze |first=Horst |title=Glass – Nature, Structure, and Properties |publisher=Springer |year=1991 |pages=3–5 |isbn=978-0-387-97396-8}}</ref> However, the term "glass" is often defined in a broader sense, to describe any non-crystalline ([[amorphous solid|amorphous]]) solid that exhibits a [[glass transition]] when heated towards the liquid state.<ref name="Horst Scholze 1991" /><ref name="Elliot84">{{Cite book |last=Elliot |first=S.R. |title=Physics of Amorphous Materials |publisher=Longman group ltd |year=1984 |pages=1–52 |isbn=0-582-44636-8}}</ref>

Glass is an [[amorphous solid]]. Although the atomic-scale structure of glass shares characteristics of the structure of a [[supercooled liquid]], glass exhibits all the mechanical properties of a solid.<ref>{{cite web|last=Neumann |first=Florin |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 |access-date=8 April 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070409022023/http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html |archive-date=9 April 2007}}</ref><ref name="Gibbs">{{cite web |last=Gibbs |first=Philip |url=http://math.ucr.edu/home/baez/physics/General/Glass/glass.html |title=Is glass liquid or solid? |access-date=21 March 2007 |url-status=live |archive-url=https://web.archive.org/web/20070329154027/http://math.ucr.edu/home/baez/physics/General/Glass/glass.html |archive-date=29 March 2007}}</ref><ref>"Philip Gibbs" ''Glass Worldwide'', (May/June 2007), pp. 14–18</ref> As in other [[amorphous solid]]s, the atomic structure of a glass lacks the long-range periodicity observed in [[Crystal structure|crystalline solids]]. Due to [[chemical bonding]] constraints, glasses do possess a high degree of short-range order with respect to local atomic [[polyhedra]].<ref>{{cite journal |last=Salmon |first=P.S. |title=Order within disorder |doi=10.1038/nmat737 |journal=Nature Materials |pmid=12618817 |volume=1 |issue=2 |year=2002 |pages=87–8|s2cid=39062607 }}</ref> The notion that glass flows to an appreciable extent over extended periods of time well below the glass transition temperature is not supported by empirical research or theoretical analysis (see [[viscosity#In solids|viscosity in solids]]). Though atomic motion at glass surfaces can be observed,<ref>{{cite journal |last1=Ashtekar |first1=Sumit |last2=Scott |first2=Gregory |last3=Lyding |first3=Joseph |last4=Gruebele |first4=Martin |year=2010 |title=Direct Visualization of Two-State Dynamics on Metallic Glass Surfaces Well Below Tg |journal=J. Phys. Chem. Lett. |volume=1 |issue=13 |pages=1941–1945 |doi=10.1021/jz100633d |arxiv=1006.1684 |s2cid=93171134 }}</ref> and a viscosity on the order of 10<sup>17</sup>–10<sup>18</sup> Pa s can be measured in glass, such a high value reinforces the fact that glass would not change shape appreciably over even large periods of time.<ref name=Elliot84 /><ref>{{cite journal |last1=Vannoni |first1=M. |last2=Sordini |first2=A. |last3=Molesini |first3=G. |year=2011 |title=Relaxation time and viscosity of fused silica glass at room temperature |journal=Eur. Phys. J. E |volume=34 |issue=9 |pages=9–14 |doi=10.1140/epje/i2011-11092-9|pmid=21947892 |s2cid=2246471 }}</ref>

=== Formation from a supercooled liquid ===
{{Main|Glass transition|Glass formation}}
{{Unsolved |physics |What is the nature of the [[Glass transition|transition]] between a fluid or regular solid and a glassy phase?
"The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition." —[[Philip Warren Anderson|P.W. Anderson]]<ref>{{cite journal |last=Anderson |first=P.W. |journal=Science |volume=267 |year=1995 |doi=10.1126/science.267.5204.1615-e |pmid=17808155 |issue=5204 |pages=1615–16 |title=Through the Glass Lightly|s2cid=28052338 }}</ref> }}
For melt quenching, if the cooling is sufficiently rapid (relative to the characteristic [[crystallization]] time) then crystallization is prevented and instead the disordered atomic configuration of the [[supercooled]] liquid is frozen into the solid state at T<sub>g</sub>. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by the [[Rigidity theory (physics)|rigidity theory]].<ref name="phillips1979">{{cite journal |last=Phillips |first=J.C. |title=Topology of covalent non-crystalline solids I: Short-range order in chalcogenide alloys |journal=Journal of Non-Crystalline Solids |year=1979 |volume=34 |issue=2 |page=153 |doi=10.1016/0022-3093(79)90033-4 |bibcode=1979JNCS...34..153P }}</ref> Generally, a glass exists in a structurally [[metastability in molecules|metastable]] state with respect to its [[Crystallinity|crystalline]] form, although in certain circumstances, for example in [[atactic]] polymers, there is no crystalline analogue of the amorphous phase.<ref name="Folmer">{{cite journal |last1=Folmer |first1=J.C.W. |last2=Franzen |first2=Stefan |title=Study of polymer glasses by modulated differential scanning calorimetry in the undergraduate physical chemistry laboratory |journal=Journal of Chemical Education |year=2003 |volume=80 |issue=7 |page=813 |doi=10.1021/ed080p813 |bibcode=2003JChEd..80..813F}}</ref>

Glass is sometimes considered to be a liquid due to its lack of a first-order [[phase transition]]<ref name=Gibbs /><ref>{{cite web|last=Loy |first=Jim |url=http://www.jimloy.com/physics/glass.htm |title=Glass Is A Liquid? |access-date=21 March 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070314004114/http://www.jimloy.com/physics/glass.htm |archive-date=14 March 2007}}</ref>
where certain [[thermodynamics|thermodynamic]] [[thermodynamic variable|variables]] such as [[volume]], [[entropy]] and [[enthalpy]] are discontinuous through the glass transition range. The [[glass transition]] 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.<ref name=Zallen83 /> However, the equilibrium theory of phase transformations does not hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.<ref name="Horst Scholze 1991" /><ref name="Elliot84" />

== Occurrence in nature ==
{{Main|Volcanic glass|Impactite|Fulgurite}}

Glass can form naturally from volcanic magma. [[Obsidian]] is a common volcanic glass with high silica (SiO<sub>2</sub>) content formed when felsic lava extruded from a volcano cools rapidly.<ref>{{cite web|url=https://geology.com/rocks/obsidian.shtml|title=Obsidian: Igneous Rock – Pictures, Uses, Properties|website=geology.com}}</ref> [[Impactite]] is a form of glass formed by the impact of a [[meteorite]], where [[Moldavite]] (found in central and eastern Europe), and [[Libyan desert glass]] (found in areas in the eastern [[Sahara]], the [[Libyan desert|deserts of eastern Libya]] and [[Western Desert (Egypt)|western Egypt]]) are notable examples.<ref>{{cite web|url=https://geology.com/meteorites/impactites.shtml|title=Impactites: Impact Breccia, Tektites, Moldavites, Shattercones|website=geology.com}}</ref> [[Vitrification]] of [[quartz]] can also occur when [[lightning]] strikes [[sand]], forming hollow, [[dendrite (crystal)|branching rootlike]] structures called [[fulgurite]]s.<ref>{{Cite book|url=https://books.google.com/books?id=cxEEAAAAQAAJ&pg=PA363|title=Land, sea and sky; or, Wonders of life and nature, tr. from the Germ. [Die Erde und ihr organisches Leben] of H.J. Klein and dr. Thomé, by J. Minshull|last=Klein|first=Hermann Joseph|date=1881-01-01}}</ref> [[Trinitite]] is a glassy residue formed from the desert floor sand at the [[Trinity test|Trinity]] [[nuclear testing|nuclear bomb test]] site.<ref>{{Cite news|url=http://www.atlasobscura.com/articles/trinitite-trinity-test-mineral-cultural-jewelry|title=The Long, Weird Half-Life of Trinitite|last=Giaimo|first=Cara|date=2017-06-30|work=Atlas Obscura|access-date=2017-07-08|language=en|df=mdy-all}}</ref> [[Edeowie glass]], found in [[South Australia]], is proposed to originate from [[Pleistocene]] grassland fires, [[lightning]] strikes, or [[hypervelocity impact]] by one or several [[asteroid]]s or [[comet]]s.<ref>{{cite journal|last1=Roperch |first1=Pierrick |last2=Gattacceca |first2=Jérôme |last3=Valenzuela |first3=Millarca |last4=Devouard |first4=Bertrand |last5=Lorand |first5=Jean-Pierre |last6=Arriagada |first6=Cesar |last7=Rochette |first7=Pierre |last8=Latorre |first8=Claudio |last9=Beck |first9=Pierre |title=Surface vitrification caused by natural fires in Late Pleistocene wetlands of the Atacama Desert|journal=Earth and Planetary Science Letters |volume=469 |issue=1 July 2017 |pages=15–26 |date=2017 |doi=10.1016/j.epsl.2017.04.009|bibcode=2017E&PSL.469...15R |s2cid=55581133 |url=https://hal.archives-ouvertes.fr/hal-02889687 }}</ref>

<gallery mode="nolines">

File:Lipari-Obsidienne (5).jpg|A piece of volcanic [[obsidian]] glass
File:Moldavite Besednice.jpg|[[Moldavite]], a natural glass formed by [[meteorite]] impact, from [[Besednice]], [[Bohemia proper|Bohemia]]
File:Fulgurites-algeria.jpg|Tube [[fulgurites]]
File:Trinitite from Trinity Site.jpg|[[Trinitite]], a glass made by the [[Trinity (nuclear test)|Trinity nuclear-weapon test]]
File:Libyan Desert Glass.jpg|[[Libyan desert glass]]
</gallery>

== History ==
{{Main|History of glass}}
[[File:Roman diatretglas.jpg|thumb|upright|Roman [[cage cup]] from the 4th century BC|alt=Refer to caption]]

Naturally occurring [[obsidian]] glass was used by [[Stone Age]] societies as it fractures along very sharp edges, making it ideal for cutting tools and weapons.<ref name="Harvey09">{{Cite book|url=https://books.google.com/books?id=7ig5XnOx4RMC&pg=PA83|pages=83–90|title=Fundamental Building Materials|last=Ward-Harvey|first=K.|date=2009|publisher=Universal-Publishers|isbn=978-1-59942-954-0}}</ref><ref>{{cite web |url=https://www.nationalgeographic.com/news/2015/04/150413-Paleolithic-obsidian-weapons-arteni-armenia-archaeology/ |title=Digs Reveal Stone-Age Weapons Industry With Staggering Output |date=13 April 2015 |website=National Geographic News}}</ref> Glassmaking dates back at least 6000 years, long before humans had discovered how to [[Smelting|smelt]] iron.<ref name="Harvey09" /> Archaeological evidence suggests that the first true synthetic glass was made in [[Lebanon]] and the coastal north [[Syria]], [[Mesopotamia]] or [[ancient Egypt]].<ref name="Henderson_ancient_glass">{{cite book |author=Julian Henderson |title=Ancient Glass |year=2013 |publisher=Cambridge University Press |doi=10.1017/CBO9781139021883.006 |pages=127–157}}</ref><ref>{{cite web |url=http://www.glassonline.com/infoserv/history.html |title=Glass Online: The History of Glass |access-date=29 October 2007 |url-status=dead |archive-url=https://web.archive.org/web/20111024000436/http://www.glassonline.com/infoserv/history.html |archive-date=24 October 2011 }}</ref> The earliest known glass objects, of the mid-third millennium BC, were [[Glass beadmaking|beads]], perhaps initially created as accidental by-products of [[metalworking]] ([[slag]]s) or during the production of [[Egyptian faience|faience]], a pre-glass [[Vitreous enamel|vitreous]] material made by a process similar to [[Ceramic glaze|glazing]].<ref>{{cite web |url=https://www.cmog.org/article/life-string-35-centuries-glass-bead |title=All About Glass &#124; Corning Museum of Glass |website=www.cmog.org}}</ref>
Early glass was rarely transparent and often contained impurities and imperfections,<ref name="Harvey09" /> and is technically faience rather than true glass, which did not appear until the 15th century BC.<ref>{{Cite journal|last=Karklins|first=Karlis|title=Simon Kwan &ndash; Early Chinese Faience and Glass Beads and Pendants|url=https://www.academia.edu/38201095|journal=BEADS: Journal of the Society of Bead Researchers|date=January 2013|language=en}}</ref> However, red-orange glass beads excavated from the [[Indus Valley civilisation|Indus Valley Civilization]] dated before 1700 BC (possibly as early as 1900 BC) predate sustained glass production, which appeared around 1600 BC in Mesopotamia and 1500 BC in Egypt.<ref>{{Cite book|last=Kenoyer|first=J.M|url=https://www.harappa.com/sites/default/files/pdf/BeadTechnologiesSummary.pdf |archive-url=https://web.archive.org/web/20190708064827/https://www.harappa.com/sites/default/files/pdf/BeadTechnologiesSummary.pdf |archive-date=2019-07-08 |url-status=live|title=South Asian Archaeology|year=2001|location=Paris|pages=157–170|chapter=Bead Technologies at Harappa, 3300-1900 BC: A Comparative Summary}}</ref><ref>{{Cite book|last=McIntosh|first=Jane|url=https://books.google.com/books?id=1AJO2A-CbccC&q=indus+valley+civilization|title=The Ancient Indus Valley: New Perspectives|date=2008|publisher=ABC-CLIO|isbn=978-1-57607-907-2|pages=99|language=en}}</ref> During the [[Late Bronze Age]] there was a rapid growth in [[glassmaking]] technology in [[Egypt]] and [[Western Asia]].<ref name="Henderson_ancient_glass" /> Archaeological finds from this period include coloured glass [[ingots]], vessels, and beads.<ref name="Henderson_ancient_glass" /><ref>{{cite web |url=https://dailyhistory.org/How_did_Manufactured_Glass_Develop_in_the_Bronze_Age? |title=How did Manufactured Glass Develop in the Bronze Age? - DailyHistory.org |website=dailyhistory.org}}</ref> Much early glass production relied on grinding techniques borrowed from [[Stonemasonry|stoneworking]], such as grinding and carving glass in a cold state.<ref>Wilde, H. "Technologische Innovationen im 2. Jahrtausend v. Chr. Zur Verwendung und Verbreitung neuer Werkstoffe im ostmediterranen Raum". GOF IV, Bd 44, Wiesbaden 2003, 25–26.</ref>

The term ''glass'' developed in the late [[Roman Empire]]. It was in the [[Roman glass]]making centre at [[Trier]] (located in current-day Germany) that the [[late-Latin]] term ''glesum'' originated, probably from a [[Germanic languages|Germanic]] word for a [[transparent materials|transparent]], [[lustrous]] substance.<ref name="douglas">{{cite book |last=Douglas |first=R.W. |title=A history of glassmaking |publisher=G T Foulis & Co Ltd |place=Henley-on-Thames |year=1972 |isbn=978-0-85429-117-5 |pages=5}}</ref> Glass objects have been recovered across the Roman Empire<ref>{{Cite book |url=https://books.google.com/books?id=bBBkBJN_lJMC&pg=PA45|title=Roman Glass in the Corning Museum of Glass, Volume 3 |last=Whitehouse |first=David |year=2003 |publisher=Hudson Hills |isbn=978-0-87290-155-1 |page=45}}</ref> in domestic, [[funerary]],<ref>{{Cite book |url=https://books.google.com/books?id=UO5MAQAAMAAJ&pg=PA365|title=The Art Journal |date=1888 |publisher=Virtue and Company |page=365}}</ref> and industrial contexts,<ref>{{Cite journal |url=https://books.google.com/books?id=ouIkAQAAMAAJ&pg=PA259|title=The Manufacture of Glass Milk Bottles |last=Brown |first=A.L. |journal=The Glass Industry |volume=2 |issue=11 |date=November 1921 |publisher=Ashlee Publishing Company |page=259}}</ref> as well as trade items in marketplaces in distant provinces.<ref>Aton, Francesca, ''[https://www.artnews.com/art-news/news/roman-glass-bowl-nijmegen-1234616630/ Perfectly Preserved 2,000-Year-Old Roman Glass Bowl Unearthed in the Netherlands]'', Art News, January 25, 2022</ref><ref>McGreevy, Nora, ''[https://www.smithsonianmag.com/smart-news/2000-year-old-ancient-roman-glass-bowl-found-in-netherlands-180979461/ 2,000-Year-Old Roman Bowl Discovered Intact in the Netherlands]'', National Geographic, January 28, 2022</ref> Examples of [[Roman glass]] have been found outside of the former [[Roman Empire]] in [[China]],<ref>{{Cite book |url=https://books.google.com/books?id=0zp6iMZoqt0C&pg=PA290|title=Six Dynasties Civilization |last=Dien |first=Albert E. |year=2007 |publisher=Yale University Press |isbn=978-0-300-07404-8 |page=290}}</ref> the [[Baltic region|Baltics]], the [[Middle East]], and [[India]].<ref>{{Cite book |url=https://books.google.com/books?id=xeJMAgAAQBAJ&pg=RA2-PA29|title=The Oxford Companion to Archaeology |last1=Silberman |first1=Neil Asher |last2=Bauer |first2=Alexander A. |year=2012 |publisher=Oxford University Press |isbn=978-0-19-973578-5 |page=29}}</ref> The Romans perfected [[cameo glass]], produced by [[Etching (microfabrication)|etching]] and carving through fused layers of different colours to produce a design in relief on the glass object.<ref name="britannica-glass">{{Cite web|url=https://www.britannica.com/technology/glass|title=glass &#124; Definition, Composition, & Facts|website=Encyclopedia Britannica}}</ref>

[[File:Vitrail-Passion.jpg|thumb|Windows in the choir of the [[Basilica of Saint-Denis]], one of the earliest uses of extensive areas of glass (early 13th-century architecture with restored glass of the 19th century)|alt=Elaborate stained glass windows in the choir of the Basilica of Saint Denis]]

In [[post-classical]] West Africa, [[Kingdom of Benin|Benin]] was a manufacturer of glass and glass beads.<ref>Oliver, Roland, and Fagan, Brian M. ''Africa in the Iron Age, c500 B.C. to A.D. 1400''. New York: Cambridge University Press, p. 187. {{ISBN|0-521-20598-0}}.</ref>
Glass was used extensively in Europe during the [[Middle Ages]]. [[Anglo-Saxon glass]] has been found across England during archaeological excavations of both settlement and cemetery sites.<ref>{{Cite book |url=https://books.google.com/books?id=idAVBAAAQBAJ&pg=PP1 |title=Neighbours and Successors of Rome: Traditions of Glass Production and use in Europe and the Middle East in the Later 1st Millennium AD |last1=Keller |first1=Daniel |last2=Price |first2=Jennifer |last3=Jackson |first3=Caroline |year=2014 |publisher=Oxbow Books |isbn=978-1-78297-398-0 |pages=1–41}}</ref> From the 10th century onwards, glass was employed in [[stained glass windows]] of churches and [[cathedral]]s, with famous examples at [[Chartres Cathedral]] and the [[Basilica of Saint-Denis]]. By the 14th century, architects were designing buildings with walls of [[stained glass]] such as [[Sainte-Chapelle]], Paris, (1203–1248) and the East end of [[Gloucester Cathedral]]. With the change in architectural style during the [[Renaissance architecture|Renaissance]] period in Europe, the use of large stained glass windows became much less prevalent,<ref>{{Cite book |url=https://archive.org/details/discoveringstain0000tuta |url-access=registration |title=Discovering Stained Glass in Detroit |last1=Tutag |first1=Nola Huse |last2=Hamilton |first2=Lucy |date=1987 |publisher=Wayne State University Press |isbn=978-0-8143-1875-1 |pages=[https://archive.org/details/discoveringstain0000tuta/page/11 11]}}</ref> although stained glass had a major revival with [[Gothic Revival architecture]] in the 19th century.<ref>{{Cite book |url=https://archive.org/details/encyclopediaofam00hunt |url-access=registration |title=Encyclopedia of American architecture |last1=Packard |first1=Robert T. |last2=Korab |first2=Balthazar |last3=Hunt |first3=William Dudley |date=1980 |publisher=McGraw-Hill |isbn=978-0-07-048010-0 |pages=[https://archive.org/details/encyclopediaofam00hunt/page/268 268]}}</ref>

During the 13th century, the island of [[Murano]], [[Venice]], became a centre for glass making, building on medieval techniques to produce colourful ornamental pieces in large quantities.<ref name=britannica-glass /> [[Venetian glass|Murano glass]] makers developed the exceptionally clear colourless glass [[cristallo]], so called for its resemblance to natural crystal, which was extensively used for windows, mirrors, ships' lanterns, and lenses.<ref name="Harvey09" /> In the 13th, 14th, and 15th centuries, enamelling and [[gilding]] on glass vessels was perfected in Egypt and Syria.<ref name="EB1911-incorp" /> Towards the end of the 17th century, [[Bohemia]] became an important region for glass production, remaining so until the start of the 20th century. By the 17th century, glass in the Venetian tradition was also being produced in [[England]]. In about 1675, [[George Ravenscroft]] invented [[lead crystal]] glass, with [[cut glass]] becoming fashionable in the 18th century.<ref name=britannica-glass /> Ornamental glass objects became an important art medium during the [[Art Nouveau]] period in the late 19th century.<ref name="britannica-glass" />

Throughout the 20th century, new [[mass production]] techniques led to widespread availability of glass in much larger amounts, making it practical as a building material and enabling new applications of glass.<ref>{{Cite book |url=https://books.google.com/books?id=jm9hGqECbXcC&pg=PA705 |title=Global Roadmap for Ceramic and Glass Technology |last=Freiman |first=Stephen |year=2007 |publisher=John Wiley & Sons |isbn=978-0-470-10491-0 |pages=705}}</ref> In the 1920s a [[Glass casting|mould]]-etch process was developed, 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 coloured 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/ |access-date=2007-10-19 |archive-date=2 December 2014 |archive-url=https://web.archive.org/web/20141202110304/http://www.glassonweb.com/articles/article/201/ |url-status=dead }}</ref> In the 1950s, [[Pilkington|Pilkington Bros.]], [[England]], developed the [[float glass]] process, producing high-quality distortion-free flat sheets of glass by floating on molten [[tin]].<ref name="Harvey09" /> Modern multi-story buildings are frequently constructed with [[curtain wall (architecture)|curtain walls]] made almost entirely of glass.<ref>{{Cite book |url=https://books.google.com/books?id=b_PmZAzJecYC&pg=PT187 |title=Sustainable Renovation: Strategies for Commercial Building Systems and Envelope |last1=Gelfand |first1=Lisa |last2=Duncan |first2=Chris |year=2011 |publisher=John Wiley & Sons |pages=187 |isbn=978-1-118-10217-6}}</ref> [[Laminated glass]] has been widely applied to vehicles for windscreens.<ref>{{Cite book |url=https://books.google.com/books?id=g-YCKEPYMpYC&pg=PA274 |title=Photodermatology |last1=Lim |first1=Henry W. |last2=Honigsmann |first2=Herbert |last3=Hawk |first3=John L.M. |year=2007 |publisher=CRC Press |pages=274 |isbn=978-1-4200-1996-4}}</ref> Optical glass for spectacles has been used since the Middle Ages.<ref>{{cite book|title=The Properties of Optical Glass|first1=Hans|last1=Bach|first2=Norbert|last2=Neuroth|publisher=Springer|year=2012|url=https://books.google.com/books?id=y3nnCAAAQBAJ&pg=PA267|isbn=978-3-642-57769-7|pages=267}}</ref> The production of lenses has become increasingly proficient, aiding [[astronomer]]s<ref>{{cite book |first1=Ian S. |last1=McLean |title=Electronic Imaging in Astronomy: Detectors and Instrumentation |url=https://books.google.com/books?id=FGHhZf-k8SkC&pg=PA78 |publisher=Springer Science & Business Media |year=2008 |pages=78 |isbn=978-3-540-76582-0}}</ref> as well as having other application in medicine and science.<ref name="glassalliance">{{cite web|url=https://www.glassallianceeurope.eu/en/applications |title=Glass Applications – Glass Alliance Europe |publisher=Glassallianceeurope.eu |access-date=2020-03-01}}</ref> Glass is also employed as the aperture cover in many [[solar energy]] collectors.<ref>{{Cite book |url=https://books.google.com/books?id=QNTKBQAAQBAJ&pg=PA122 |title=Solar Energy Sciences and Engineering Applications |last1=Enteria |first1=Napoleon |last2=Akbarzadeh |first2=Aliakbar |pages=122 |year=2013 |publisher=CRC Press |isbn=978-0-203-76205-9}}</ref>

In the 21st century, glass manufacturers have developed different brands of [[chemically strengthened glass]] for widespread application in [[touchscreen]]s for [[smartphone]]s, [[tablet computer]]s, and many other types of [[information appliance]]s. These include [[Gorilla Glass]], developed and manufactured by [[Corning Inc.|Corning]], [[AGC Inc.]]'s [[Dragontrail]] and [[Schott AG]]'s Xensation.<ref>{{cite web |url=http://www.physnews.com/materials-news/cluster251747226/ |title=Gorilla Glass maker unveils ultra-thin and flexible Willow Glass |work=Physics News |access-date=2013-11-01 |url-status=dead |archive-url=https://web.archive.org/web/20131106075448/http://www.physnews.com/materials-news/cluster251747226/ |archive-date=6 November 2013 }}</ref><ref>{{cite web |url=http://www.schott.com/xensation/english/index.html |title=Xensation |publisher=[[Schott AG|Schott]] |access-date=2013-11-01 |url-status=live |archive-url=https://web.archive.org/web/20131103224742/http://www.schott.com/xensation/english/index.html |archive-date=2013-11-03 }}</ref><ref name="gensix">{{cite web |url=https://www.engadget.com/2018/07/18/corning-unveils-gorilla-glass-6/ |title=Gorilla Glass 6 gives phones a better shot at surviving multiple drops |publisher=Engadget |date=19 July 2018 |first=Jon |last=Fingas }}</ref>

== Physical properties ==
=== Optical ===
Glass is in widespread use in optical systems due to its ability to refract, reflect, and transmit light following [[geometrical optics]]. The most common and oldest applications of glass in optics are as [[Lens (optics)|lenses]], [[window]]s, [[mirror]]s, and [[Prism (optics)|prism]]s.<ref name="Bach12">{{cite book |title=The Properties of Optical Glass |first1=Hans |last1=Bach |first2=Norbert |last2=Neuroth |publisher=Springer |year=2012|url=https://books.google.com/books?id=y3nnCAAAQBAJ&pg=PA1 |pages=1–11 |isbn=978-3-642-57769-7}}</ref> The key optical properties [[refractive index]], [[Dispersion (optics)|dispersion]], and [[Transparency and translucency|transmission]], of glass are strongly dependent on chemical composition and, to a lesser degree, its thermal history.<ref name=Bach12 /> Optical glass typically has a refractive index of 1.4 to 2.4, and an [[Abbe number]] (which characterises dispersion) of 15 to 100.<ref name=Bach12 /> Refractive index may be modified by high-density (refractive index increases) or low-density (refractive index decreases) additives.<ref>{{Cite book |url=https://books.google.com/books?id=-0DOBQAAQBAJ&pg=PA70 |title=Physical Properties of Materials, Second Edition |last=White |first=Mary Anne |authorlink1=Mary Anne White |year=2011 |pages=70 |publisher=CRC Press|isbn=978-1-4398-9532-0}}</ref>

Glass transparency results from the absence of [[grain boundary|grain boundaries]] which [[diffuse reflection|diffusely scatter light]] in polycrystalline materials.<ref name="Carter-Norton">{{Cite book |url=https://books.google.com/books?id=aE_VQ8I24OoC&pg=PA583 |title=Ceramic Materials: Science and Engineering |last1=Carter |first1=C. Barry |first2=M. Grant |last2= Norton |year=2007| publisher=Springer Science & Business Media| pages=583|isbn=978-0-387-46271-4 }}</ref> Semi-opacity due to crystallization may be induced in many glasses by maintaining them for a long period at a temperature just insufficient to cause fusion. In this way, the crystalline, devitrified material, known as Réaumur's glass [[porcelain]] is produced.<ref name="EB1911-incorp">{{EB1911|inline=1 |wstitle=Glass |volume=12 |page=86}}</ref><ref name="Mysen05">{{cite book|last1=Mysen|first1=Bjorn O.|last2=Richet|first2=Pascal|title=Silicate Glasses and Melts: Properties and Structure|publisher=Elsevier|year=2005|pages=10}}</ref> Although generally transparent to visible light, glasses may be [[Opacity (optics)|opaque]] to other [[Electromagnetic spectrum|wavelengths of light]]. While silicate glasses are generally opaque to [[infrared]] wavelengths with a transmission cut-off at 4 μm, heavy-metal [[Fluoride glass|fluoride]] and [[Chalcogenide glass|chalcogenide]] glasses are transparent to infrared wavelengths of 7 to 18 μm.<ref name=brittanica-industrial /> The addition of metallic oxides results in different coloured glasses as the metallic ions will absorb wavelengths of light corresponding to specific colours.<ref name=brittanica-industrial />

=== Other ===
{{See also|List of physical properties of glass|Corrosion#Corrosion of glass|Strength of glass}}
[[File:Artesanía en vidrio (Unsplash).jpg|thumb|Glass can be fairly easily melted and manipulated with a heat source]]
In the manufacturing process, glasses can be poured, formed, extruded and moulded into forms ranging from flat sheets to highly intricate shapes.<ref>{{Cite book |url=https://books.google.com/books?id=BZUtFQNuNgMC&pg=PA60 |title=Handbook of Physical Vapor Deposition (PVD) Processing |last=Mattox |first=D.M. |year=2014 |page=60 |publisher=Cambridge University Press |isbn=978-0-08-094658-0}}</ref> The finished product is brittle but can be [[laminated glass|laminated]] or [[Tempered glass|tempered]] to enhance durability.<ref>{{Cite book|url=https://books.google.com/books?id=D7Z8ywb3QggC&pg=PA361|title=Glasses and the Vitreous State|last=Zarzycki|first=Jerzy|year=1991|publisher=Cambridge University Press|isbn=978-0-521-35582-7|pages=361}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=CL8Z38FaPsAC&pg=PA365|title=Collision Repair and Refinishing: A Foundation Course for Technicians|last1=Thomas|first1=Alfred|last2=Jund|first2=Michael|year=2013|pages=365|isbn=978-1-133-60187-6}}</ref> Glass is typically inert, resistant to chemical attack, and can mostly withstand the action of water, making it an ideal material for the manufacture of containers for foodstuffs and most chemicals.<ref name="Harvey09" /><ref name="Gardner-1949">{{Cite book|url=https://books.google.com/books?id=yYQ3BMs9Ql0C&pg=PA13|title=Research and Development in Applied Optics and Optical Glass at the National Bureau of Standards: A Review and Bibliography|last1=Gardner|first1=Irvine Clifton|last2=Hahner|first2=Clarence H.|date=1949|publisher=U.S. Government Printing Office|page=13|isbn=9780598682413}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=rJTBCQAAQBAJ&pg=PA550|title=Food Safety in the 21st Century: Public Health Perspective|last1=Dudeja|first1=Puja|last2=Gupta|first2=Rajul K.| page=550 |last3=Minhas|first3=Amarjeet Singh|year=2016|publisher=Academic Press|isbn=978-0-12-801846-0}}</ref> Nevertheless, although usually highly resistant to chemical attack, glass will corrode or dissolve under some conditions.<ref name="Gardner-1949" /><ref name="Bengisu 2013">{{Cite book|url=https://books.google.com/books?id=PXD8CAAAQBAJ&pg=PA360|title=Engineering Ceramics|last=Bengisu|first=M.|year=2013|publisher=Springer Science & Business Media|isbn=978-3-662-04350-9|page=360}}</ref> The materials that make up a particular glass composition have an effect on how quickly the glass corrodes. Glasses containing a high proportion of [[alkali metal|alkali]] or [[Alkaline earth element|alkaline earth]] elements are more susceptible to corrosion than other glass compositions.<ref>{{Cite book|url=https://books.google.com/books?id=IVe7CgAAQBAJ&pg=PA141|title=Materials Degradation and Its Control by Surface Engineering|last1=Batchelor|first1=Andrew W.|last2=Loh|first2=Nee Lam|last3=Chandrasekaran|first3=Margam|year=2011|publisher=World Scientific|page=141|isbn=978-1-908978-14-1}}</ref><ref name="Chawla93">{{Cite book|url=https://books.google.com/books?id=_NXYRgHnnqkC&pg=PA328|pages=327–328|title=Materials Selection for Corrosion Control|last=Chawla|first=Sohan L.|date=1993|publisher=ASM International|isbn=978-1-61503-728-5}}</ref>

The density of glass varies with chemical composition with values ranging from {{convert|2.2|g/cm3|kg/m3}} for [[Fused quartz|fused silica]] to {{convert|7.2|g/cm3|kg/m3}} for dense flint glass.<ref>{{cite Q|Q87511351}}<!--"Density of Glass" in The Physics Factbook--></ref> Glass is stronger than most metals, with a theoretical [[tensile strength]] for pure, flawless glass estimated at {{convert|14|to|35|GPa|psi}} due to its ability to undergo reversible compression without fracture. However, the presence of scratches, bubbles, and other microscopic flaws lead to a typical range of {{convert|14|to|175|MPa|psi}} in most commercial glasses.<ref name="brittanica-industrial">{{Cite web|url=https://www.britannica.com/topic/glass-properties-composition-and-industrial-production-234890|title=Industrial glass – Properties of glass|website=Encyclopedia Britannica}}</ref> Several processes such as [[Toughened glass|toughening]] can increase the strength of glass.<ref>{{cite web|url=https://www.pilkington.com/en-gb/uk/architects/glass-information/functions-of-glass/mechanicalfunctionsofglass/glass-strength|title=Glass Strength|website=www.pilkington.com|access-date=2017-11-24|url-status=live|archive-url=https://web.archive.org/web/20170726123604/http://www.pilkington.com/en-gb/uk/architects/glass-information/functions-of-glass/mechanicalfunctionsofglass/glass-strength|archive-date=26 July 2017}}</ref> Carefully drawn flawless [[glass fibre]]s can be produced with strength of up to {{convert|11.5|GPa|psi}}.<ref name=brittanica-industrial />
{{Further|topic=the tiny glass flakes formed during glass vial manufacturing |Spicule (glass manufacture)|label1=Spicule}}

=== Reputed flow ===
The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass has exhibited the liquid property of flowing from one shape to another.<ref>{{cite news|url=https://www.nytimes.com/2008/07/29/science/29glass.html?ex=1375070400&en=048ade4011756b24&ei=5124&partner=permalink&exprod=permalink|title=The Nature of Glass Remains Anything but Clear|work=The New York Times|access-date=29 July 2008|date=29 July 2008|author=Kenneth Chang|url-status=live|archive-url=https://web.archive.org/web/20090424094929/http://www.nytimes.com/2008/07/29/science/29glass.html?ex=1375070400&en=048ade4011756b24&ei=5124&partner=permalink&exprod=permalink|archive-date=24 April 2009}}</ref> This assumption is incorrect, as once solidified, glass stops flowing. The sags and ripples observed in old glass were already there the day it was made; manufacturing processes used in the past produced sheets with imperfect surfaces and non-uniform thickness (the near-perfect [[float glass]] used today only became widespread in the 1960s).<ref name=Gibbs />

A 2017 study computed the rate of flow of the medieval glass used in [[Westminster Abbey]] from the year 1268. The study found that the room temperature viscosity of this glass was roughly 10<sup>24</sup>{{nbsp}}[[Pascal (unit)|Pa]]·[[Second|s]] which is about 10<sup>16</sup> times less viscous than a previous estimate made in 1998, which focused on soda-lime silicate glass. Even with this lower viscosity, the study authors calculated that the maximum flow rate of medieval glass is 1[[Nanometer|nm]] per billion years, making it impossible to observe in a human timescale.<ref>{{cite journal | last1=Gulbiten | first1=Ozgur | last2=Mauro | first2=John C. | last3=Guo | first3=Xiaoju | last4=Boratav | first4=Olus N. | title=Viscous flow of medieval cathedral glass | journal=Journal of the American Ceramic Society| volume=101 | issue=1 | date=3 August 2017 | issn=0002-7820 | doi=10.1111/jace.15092 | pages=5–11}}</ref><ref>{{Cite web |title=Glass viscosity calculations definitively debunk the myth of observable flow in medieval windows |last=Gocha |first=April |work=The American Ceramic Society |date=3 August 2017 |url= https://ceramics.org/ceramic-tech-today/glass-viscosity-calculations-definitively-debunk-the-myth-of-observable-flow-in-medieval-windows}}</ref>

== Types ==
=== Silicate ===
[[File:Quartz sand.jpg|thumb|[[Sand|Quartz sand]] (silica) is the main raw material in commercial glass production|alt=Close-up photograph of sand]]
[[Silicon dioxide]] (SiO<sub>2</sub>) is a common fundamental constituent of glass. [[Fused quartz]] is a glass made from chemically pure silica.<ref name="Chawla93" /> It has very low thermal expansion and excellent resistance to [[thermal shock]], being able to survive immersion in water while red hot, resists high temperatures (1000–1500&nbsp;°C) and chemical weathering, and is very hard. It is also transparent to a wider spectral range than ordinary glass, extending from the visible further into both the [[UV]] and [[Infrared|IR]] ranges, and is sometimes used where transparency to these wavelengths is necessary. Fused quartz is used for high-temperature applications such as furnace tubes, lighting tubes, melting crucibles, etc.<ref name="Seafriends-1994">{{cite web|url=http://www.seafriends.org.nz/oceano/seasand.htm|title=Mining the sea sand|url-status=live|archive-url=https://web.archive.org/web/20120229061512/http://www.seafriends.org.nz/oceano/seasand.htm|archive-date=29 February 2012|website=Seafriends|date=1994-02-08|access-date=2012-05-15}}</ref> However, its high melting temperature (1723&nbsp;°C) and viscosity make it difficult to work with. Therefore, normally, other substances (fluxes) are added to lower the melting temperature and simplify glass processing.<ref name="Chemistry-explained">{{cite web|url=http://www.chemistryexplained.com/Ge-Hy/Glass.html|access-date=1 April 2015|title=Glass – Chemistry Encyclopedia|url-status=live|archive-url=https://web.archive.org/web/20150402113454/http://www.chemistryexplained.com/Ge-Hy/Glass.html|archive-date=2 April 2015}}</ref>

==== Soda–lime ====
[[Sodium carbonate]] (Na<sub>2</sub>CO<sub>3</sub>, "soda") is a common additive and acts to lower the glass-transition temperature. However, [[sodium silicate]] is [[water solubility|water-soluble]], so [[lime (mineral)|lime]] (CaO, [[calcium oxide]], generally obtained from [[limestone]]), along with [[magnesium oxide]] (MgO), and [[aluminium oxide]] (Al<sub>2</sub>O<sub>3</sub>), are commonly added to improve chemical durability. Soda–lime glasses (Na<sub>2</sub>O) + lime (CaO) + magnesia (MgO) + alumina (Al<sub>2</sub>O<sub>3</sub>) account for over 75% of manufactured glass, containing about 70 to 74% silica by weight.<ref name="Chawla93" /><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|978-3-527-20112-9}}, pp. 365–432.</ref> Soda–lime–silicate glass is transparent, easily formed, and most suitable for window glass and tableware.<ref name="Spence-2016">{{Cite book|url=https://books.google.com/books?id=KX5TCwAAQBAJ&pg=PA509|title=Construction Materials, Methods and Techniques|last1=Spence|first1=William P.|last2=Kultermann|first2=Eva|year=2016|publisher=Cengage Learning|isbn=978-1-305-08627-2|pages=510–526}}</ref> However, it has a high thermal expansion and poor resistance to heat.<ref name="Spence-2016" /> Soda–lime glass is typically used for [[window]]s, [[bottle]]s, [[light bulb]]s, and [[jar]]s.<ref name="Chemistry-explained" />

==== Borosilicate ====
[[File:Measuring cup.jpg|thumb|A [[Pyrex]] [[borosilicate glass]] [[measuring cup]] |alt=Refer to caption]]
[[Borosilicate glass]]es (e.g. [[Pyrex]], [[Duran (glass)|Duran]]) typically contain 5–13% [[boron trioxide]] (B<sub>2</sub>O<sub>3</sub>).<ref name="Chemistry-explained" /> Borosilicate glasses have fairly low [[Coefficient of thermal expansion|coefficients of thermal expansion]] (7740 Pyrex CTE is 3.25{{e|-6}}/°C<ref>{{cite web|url=http://www.quartz.com/pxprop.pdf|title=Properties of PYREX®, PYREXPLUS® and Low Actinic PYREX Code 7740 Glasses|publisher=Corning, Inc.|url-status=live|archive-url=https://web.archive.org/web/20120113050839/http://www.quartz.com/pxprop.pdf|archive-date=13 January 2012|access-date=2012-05-15}}</ref> as compared to about 9{{e|-6}}/°C for a typical soda–lime glass<ref>{{cite web|url=http://www.us.schott.com/tubing/media/selector/datasheets/english/schott-tubing_datasheet_ar-glas_english.pdf|title=AR-GLAS® Technical Data|url-status=live|archive-url=https://web.archive.org/web/20120612224929/http://www.us.schott.com/tubing/media/selector/datasheets/english/schott-tubing_datasheet_ar-glas_english.pdf|archive-date=12 June 2012|publisher=Schott, Inc.}}</ref>). They are, therefore, less subject to [[Stress (mechanics)|stress]] caused by [[thermal expansion]] and thus less vulnerable to [[Crack propagation|cracking]] from [[thermal shock]]. They are commonly used for e.g. [[labware]], [[cookware|household cookware]], and sealed beam car [[head lamp]]s.<ref name="Chemistry-explained" />

==== Lead ====
The addition of [[lead(II) oxide]] into silicate glass lowers melting point and [[viscosity]] of the melt.<ref>{{Cite book |url=https://books.google.com/books?id=ZeF_QLW6-xsC&pg=PA125 |title=Introduction to Glass Science and Technology |last=Shelby |first=J.E. |year=2017 |page=125 |publisher=Royal Society of Chemistry |isbn=978-0-85404-639-3}}</ref> The high density of [[lead glass]] (silica + lead oxide (PbO) + potassium oxide (K<sub>2</sub>O) + soda (Na<sub>2</sub>O) + zinc oxide (ZnO) + alumina) results in a high electron density, and hence high refractive index, making the look of glassware more brilliant and causing noticeably more [[specular reflection]] and increased [[Dispersion (optics)|optical dispersion]].<ref name="Chawla93" /><ref name="Schwartz-2002">{{Cite book |url=https://books.google.com/books?id=0ETMBQAAQBAJ&pg=PA352 |title=Encyclopedia of Materials, Parts and Finishes |edition=Second |last=Schwartz |first=Mel |year=2002 |page =352 |publisher=CRC Press |isbn=978-1-4200-1716-8}}</ref> Lead glass has a high elasticity, making the glassware more workable and giving rise to a clear "ring" sound when struck. However, lead glass cannot withstand high temperatures well.<ref name="Seafriends-1994" /> Lead oxide also facilitates solubility of other metal oxides and is used in coloured glass. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glass); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in [[vitreous enamel]]s and [[glass solder]]s. The high [[ionic radius]] of the Pb<sup>2+</sup> ion renders it highly immobile and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda–lime glass (10<sup>8.5</sup> vs 10<sup>6.5</sup>&nbsp;Ω⋅cm, [[direct current|DC]] at 250&nbsp;°C).<ref>{{Cite book|url=https://books.google.com/books?id=ASIYuNCp81YC&pg=PA158|title=Ceramic and Glass Materials: Structure, Properties and Processing|last1=Shackelford|first1=James F.|last2=Doremus|first2=Robert H.|date=2008-04-12|publisher=Springer Science & Business Media|isbn=978-0-387-73362-3 |page=158}}</ref>

==== Aluminosilicate ====
Aluminosilicate glass typically contains 5–10% [[alumina]] (Al<sub>2</sub>O<sub>3</sub>). Aluminosilicate glass tends to be more difficult to melt and shape compared to borosilicate compositions, but has excellent thermal resistance and durability.<ref name="Chemistry-explained" /> Aluminosilicate glass is extensively used for [[fiberglass]],<ref name="Askeland-2008">{{Cite book|url=https://books.google.com/books?id=TL4j-jDXsk0C&pg=PA485|title=Essentials of Materials Science & Engineering|last1=Askeland|first1=Donald R.|last2=Fulay|first2=Pradeep P.|year=2008|page=485|publisher=Cengage Learning|isbn=978-0-495-24446-2}}</ref> used for making glass-reinforced plastics (boats, fishing rods, etc.), top-of-stove cookware, and halogen bulb glass.<ref name="Seafriends-1994" /><ref name="Chemistry-explained" />

==== Other oxide additives ====
The addition of [[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 eyeglasses.<ref>{{cite web|url=http://www.historyofglass.com/glass-making-process/glass-ingredients/|title=Glass Ingredients – What is Glass Made Of?|website=www.historyofglass.com|access-date=2017-04-23|url-status=live|archive-url=https://web.archive.org/web/20170423155431/http://www.historyofglass.com/glass-making-process/glass-ingredients/|archive-date=23 April 2017}}</ref> Iron can be incorporated into glass to absorb [[infrared]] radiation, for example in heat-absorbing filters for movie projectors, while [[cerium(IV) oxide]] can be used for glass that absorbs [[ultraviolet]] wavelengths.<ref>{{cite book |last=Pfaender |first=Heinz G. |title=Schott guide to glass |url=https://books.google.com/books?id=v5q4Hje3iFgC&pg=PA135 |access-date=8 February 2011 |year=1996 |publisher=Springer |isbn=978-0-412-62060-7 |pages=135, 186 |url-status=live |archive-url=https://web.archive.org/web/20130525185349/http://books.google.com/books?id=v5q4Hje3iFgC&pg=PA135 |archive-date=25 May 2013}}</ref> [[Fluorine]] lowers the [[dielectric constant]] of glass. Fluorine is highly [[electronegative]] and lowers the polarizability of the material. Fluoride silicate glasses are used in manufacture of [[integrated circuit]]s as an insulator.<ref>{{cite book |last1=Doering |first1=Robert |last2=Nishi |first2=Yoshio |url=https://books.google.com/books?id=PsVVKz_hjBgC&pg=SA12-PA3 |title=Handbook of semiconductor manufacturing technology |pages=12–13 |publisher=CRC Press |year=2007 |isbn=978-1-57444-675-3}}</ref>

==== Glass-ceramics ====
{{Main|Glass-ceramic}}
[[File:Ceranfeld.jpg|thumb|A high-strength glass-ceramic [[cooktop]] with negligible [[thermal expansion]] |alt=A cooktop with two of its eyes turned on]]
[[Glass-ceramic]] materials contain both non-crystalline glass and [[Crystallinity|crystalline]] [[ceramic]] phases. They are formed by controlled nucleation and partial crystallisation of a base glass by heat treatment.<ref name="Holand-glass-ceramics">{{cite book |url=https://books.google.com/books?id=Bw_Yz52jdFQC&pg=PA1 |title=Glass Ceramic Technology |last1=Holand |first1=Wolfram |last2=Beall |first2=George H. |year=2012 |pages=1–38 |publisher=John Wiley & Sons |isbn=978-1-118-26592-5}}</ref> Crystalline grains are often embedded within a non-crystalline intergranular phase of [[grain boundary|grain boundaries]]. Glass-ceramics exhibit advantageous thermal, chemical, biological, and dielectric properties as compared to metals or organic polymers.<ref name=Holand-glass-ceramics />

The most commercially important property of glass-ceramics is their imperviousness to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking and industrial processes. The negative [[thermal expansion]] coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of [[glass-ceramic]] exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000&nbsp;°C.<ref name="MOD">{{cite book |last=Richerson |first=David W. |title=Modern ceramic engineering : properties, processing and use in design |year=1992 |publisher=Dekker |pages=577–578 |location=New York |isbn=978-0-8247-8634-2 |edition=2nd}}</ref><ref name=Holand-glass-ceramics />

==== Fibreglass ====
{{Main|Fiberglass|Glass wool}}
[[Fibreglass]] (also called glass fibre reinforced plastic, GRP) is a [[composite material]] made by reinforcing a plastic [[resin]] with [[glass fibre]]s. It is made by melting glass and stretching the glass into fibres. These fibres are woven together into a cloth and left to set in a plastic resin.<ref name="Parkyn">{{cite book |url=https://books.google.com/books?id=gfEkBQAAQBAJ&pg=PA3 |title=Glass Reinforced Plastics |last=Parkyn |first=Brian |publisher=Elsevier |year=2013 |pages=3–41|isbn=978-1-4831-0298-6 }}</ref><ref>{{cite book |last= Mayer |first= Rayner M. |title= Design with reinforced plastics |page= 7 |publisher= Springer |year= 1993 |url= https://books.google.com/books?id=XQFJego9nGUC&pg=PA7 |isbn= 978-0-85072-294-9}}</ref><ref name="propertiesofmatter">{{cite web|url=http://www.propertiesofmatter.si.edu/teamwork.html|title=Properties of Matter Reading Selection: Perfect Teamwork|website=www.propertiesofmatter.si.edu|access-date=2017-04-25|url-status=dead|archive-url=https://web.archive.org/web/20160512174222/http://www.propertiesofmatter.si.edu/teamwork.html|archive-date=12 May 2016}}</ref>
Fibreglass has the properties of being lightweight and corrosion resistant, and is a good [[Insulator (electricity)|insulator]] enabling its use as [[building insulation materials|building insulation material]] and for electronic housing for consumer products. Fibreglass was originally used in the United Kingdom and United States during [[World War II]] to manufacture [[radome]]s. Uses of fibreglass include building and construction materials, boat hulls, car body parts, and aerospace composite materials.<ref name="brittanica-fibreglass">{{Cite web|url=https://www.britannica.com/technology/fiberglass|title=Fibreglass &#124; glass|website=Encyclopedia Britannica}}</ref><ref name=Parkyn /><ref name=propertiesofmatter />

[[Glass wool|Glass-fibre wool]] is an excellent [[thermal insulation|thermal]] and [[sound insulation|sound]] insulation material, commonly used in buildings (e.g. [[attic]] and [[cavity wall insulation]]), and plumbing (e.g. [[pipe insulation]]), and [[soundproofing]].<ref name=brittanica-fibreglass /> It is produced by forcing molten glass through a fine mesh by [[centripetal force]], and breaking the extruded glass fibres into short lengths using a stream of high-velocity air. The fibres are bonded with an adhesive spray and the resulting wool mat is cut and packed in rolls or panels.<ref name=brittanica-industrial />

=== Non-silicate ===
[[File:CD-RW bottom.jpg|thumb|A [[CD-RW]] (CD). [[Chalcogenide glass]] form the basis of rewritable CD and DVD solid-state memory technology.<ref name="Greer05">{{cite journal |last1=Greer |first1=A. Lindsay |doi=10.1038/4371246a |journal=Nature |volume=437 |pages=1246–1247 |year=2005 |title=Materials science: Changing Face of the Chameleon |pmid=16251941 |last2=Mathur |first2=N |issue=7063 |bibcode=2005Natur.437.1246G|s2cid=6972351 |doi-access=free }}</ref>|alt=A CD]]
Besides common silica-based glasses many other [[inorganic]] and [[Organic chemistry|organic]] materials may also form glasses, including [[Metallic glass|metals]], [[aluminate]]s, [[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, [[plastics]], [[acrylic glass|acrylic]], and many other substances.<ref name="Elliot84" /> Some of these glasses (e.g. [[Germanium dioxide]] (GeO<sub>2</sub>, Germania), in many respects a structural analogue of silica, [[fluoride glass|fluoride]], [[aluminate]], [[phosphate glass|phosphate]], [[borate glass|borate]], and [[chalcogenide glass|chalcogenide]] glasses) have physico-chemical properties useful for their application in [[Optical fiber|fibre-optic]] [[waveguide]]s in communication networks and other specialised technological applications.<ref>{{Cite book|url=https://books.google.com/books?id=gL-RDgAAQBAJ&pg=PA214|title=Technological Advances in Tellurite Glasses: Properties, Processing, and Applications|last1=Rivera|first1=V. A. G.|last2=Manzani|first2=Danilo|date=2017-03-30|publisher=Springer|isbn=978-3-319-53038-3|page=214|language=en}}</ref><ref>{{Cite journal
  |last1=Jiang|first1=Xin|last2=Lousteau|first2=Joris|last3=Richards|first3=Billy|last4=Jha|first4=Animesh|date=2009-09-01
  |title=Investigation on germanium oxide-based glasses for infrared optical fibre development
  |journal=Optical Materials|volume=31|issue=11|pages=1701–1706|doi=10.1016/j.optmat.2009.04.011  |bibcode=2009OptMa..31.1701J
}}</ref>

Silica-free glasses may often have poor glass forming tendencies. Novel techniques, including containerless processing by [[aerodynamic levitation]] (cooling the melt whilst it floats on a gas stream) or [[splat quenching]] (pressing the melt between two metal anvils or rollers), may be used to increase cooling rate, or to reduce crystal nucleation triggers.<ref>{{cite journal|author1=J. W. E. Drewitt|author2=S. Jahn|author3=L. Hennet|title=Configurational constraints on glass formation in the liquid calcium aluminate system|journal=Journal of Statistical Mechanics: Theory and Experiment|year=2019|volume=2019|issue=10|page=104012|doi=10.1088/1742-5468/ab47fc|arxiv=1909.07645|bibcode=2019JSMTE..10.4012D|s2cid=202583753}}</ref><ref>{{cite journal|author1=C. J. Benmore |author2=J. K. R. Weber|year=2017|title=Aerodynamic levitation, supercooled liquids and glass formation|journal=Advances in Physics: X|volume=2|issue=3|pages=717–736|doi= 10.1080/23746149.2017.1357498|bibcode=2017AdPhX...2..717B|doi-access=free}}</ref><ref>{{cite journal|last=Davies|first=H. A.|author2=Hull J. B. |title=The formation, structure and crystallization of non-crystalline nickel produced by splat-quenching|journal=Journal of Materials Science|year=1976|volume=11|issue=2|pages=707–717|doi=10.1007/BF00551430|bibcode=1976JMatS..11..215D|s2cid=137403190}}</ref>

==== Amorphous metals ====
{{Main|Amorphous metal}}
[[File:Bulk Metallic Glass Sample.jpg|thumb|Samples of amorphous metal, with millimeter scale|alt=Refer to caption]]
In the past, small batches of [[amorphous metal]]s with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk.<ref name=klement60>{{cite journal | last1=Klement | first1=W. Jr. |last2=Willens |first2=R.H. |last3=Duwez |first3=Pol |doi=10.1038/187869b0 |bibcode=1960Natur.187..869K |title=Non-crystalline Structure in Solidified Gold-Silicon Alloys |year=1960 |journal=Nature |volume=187 |issue=4740 |page=869|s2cid=4203025 }}</ref><ref name=lieb76>{{cite journal |last1=Liebermann |first1=H. |last2=Graham |first2=C. |doi=10.1109/TMAG.1976.1059201 |title=Production of Amorphous Alloy Ribbons and Effects of Apparatus Parameters on Ribbon Dimensions |journal=IEEE Transactions on Magnetics |year=1976 |volume=12 |issue=6 |page=921 |bibcode=1976ITM....12..921L}}</ref>

A number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). [[Liquidmetal|Liquidmetal Technologies]] sell a number of [[zirconium]]-based BMGs.

Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.<ref name=ponn04>{{cite journal |last1=Ponnambalam |first1=V. |last2=Poon |first2=S. Joseph |last3=Shiflet |first3=Gary J. |title=Fe-based bulk metallic glasses with diameter thickness larger than one centimeter |journal=Journal of Materials Research |year=2004 |volume=19 |issue=5 |page=1320 |doi=10.1557/JMR.2004.0176 |bibcode=2004JMatR..19.1320P|s2cid=138846816 }}</ref>

Experimental evidence indicates that the system Al-Fe-Si may undergo a ''first-order transition'' to an amorphous form (dubbed "q-glass") on rapid cooling from the melt. [[Transmission electron microscopy]] (TEM) images indicate that q-glass nucleates from the melt as discrete particles with a uniform spherical growth in all directions. While [[x-ray diffraction]] reveals the isotropic nature of q-glass, a [[nucleation]] barrier exists implying an interfacial discontinuity (or internal surface) between the glass and melt phases.<ref>{{cite web|url=http://www.metallurgy.nist.gov/techactv2004/TechnicalHighlights.html#glass|title=Metallurgy Division Publications|work=NIST Interagency Report 7127|url-status=live|archive-url=https://web.archive.org/web/20080916063500/http://www.metallurgy.nist.gov/techactv2004/TechnicalHighlights.html#glass|archive-date=16 September 2008}}</ref><ref>{{cite journal |last1=Mendelev |first1=M.I. |last2=Schmalian |first2=J. |last3=Wang |first3=C.Z. |last4=Morris |first4=J.R. |author5=K.M. Ho |doi=10.1103/PhysRevB.74.104206 |bibcode=2006PhRvB..74j4206M |title=Interface Mobility and the Liquid-Glass Transition in a One-Component System |year=2006 |journal=Physical Review B |volume=74 |issue=10|page=104206 |url=https://zenodo.org/record/1233751 }}</ref>

==== Polymers ====
Important polymer glasses include amorphous and glassy pharmaceutical compounds. These are useful because the solubility of the compound is greatly increased when it is amorphous compared to the same crystalline composition. Many emerging pharmaceuticals are practically insoluble in their crystalline forms.<ref>{{cite web|url=http://www-ics.u-strasbg.fr/etsp//research/glass/field.php|archive-url=https://web.archive.org/web/20160525003628/http://www-ics.u-strasbg.fr/etsp/research/glass/field.php|url-status=dead|title=A main research field: Polymer glasses|archive-date=25 May 2016|website=www-ics.u-strasbg.fr}}</ref> Many polymer [[thermoplastic]]s familiar from everyday use are glasses. For many applications, like [[glass bottles]] or [[eyewear]], polymer glasses ([[acrylic glass]], [[polycarbonate]] or [[polyethylene terephthalate]]) are a lighter alternative to traditional glass.<ref name="Carraher-polymer">{{cite book|url=https://books.google.com/books?id=_izOBgAAQBAJ&q=polymer%20glass%20lighter%20alternative&pg=PA274|title=Introduction to Polymer Chemistry|first=Charles E. Jr.|last=Carraher|year=2012|pages=274|publisher=CRC Press|isbn=978-1-4665-5495-5}}</ref>

=== Molecular liquids and molten salts ===
Molecular liquids, [[electrolyte]]s, [[molten salt]]s, and [[aqueous solution]]s are mixtures of different [[molecules]] or [[ion]]s that do not form a covalent network but interact only through weak [[van der Waals force]]s or through transient [[hydrogen bond]]s. In a mixture of three or more ionic species of dissimilar size and shape, crystallization can be so difficult that the liquid can easily be supercooled into a glass.<ref>{{Cite book|page=21|chapter-url=https://books.google.com/books?id=-ajaBwAAQBAJ&pg=PA21|chapter=Crystals, Supercooled Liquids, and Glasses in Frozen Aqueous Solutions|first1=S.L.|last1=Ruby|first2=I.|last2=Pelah|title=Mössbauer Effect Methodology: Volume 6 Proceedings of the Sixth Symposium on Mössbauer Effect Methodology New York City, January 25, 1970|editor-last=Gruverman|editor-first=Irwin J.|year=2013|publisher=Springer Science & Business Media|isbn=978-1-4684-3159-9}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=om31BwAAQBAJ&pg=PA226|title=Water Relationships in Foods: Advances in the 1980s and Trends for the 1990s|last1=Levine|first1=Harry|last2=Slade|first2=Louise|author-link2=Louise Slade|year=2013|publisher=Springer Science & Business Media|isbn=978-1-4899-0664-9|page=226}}</ref> Examples include LiCl:''R''H<sub>2</sub>O (a solution of [[lithium chloride]] salt and water molecules) in the composition range 4<''R''<8.<ref>{{Cite journal|vauthors=Dupuy J, Jal J, Prével B, Aouizerat-Elarby A, Chieux P, Dianoux AJ, Legrand J|s2cid=39468740|date=October 1992|title=Vibrational dynamics and structural relaxation in aqueous electrolyte solutions in the liquid, undercooled liquid and glassy states|journal=Journal de Physique IV |volume=2|issue=C2|pages=C2-179–C2-184|doi=10.1051/jp4:1992225|bibcode=1992JPhy4...2C.179D|url=https://hal.archives-ouvertes.fr/jpa-00251296/file/ajp-jp4199202C225.pdf |archive-url=https://web.archive.org/web/20200509082002/https://hal.archives-ouvertes.fr/jpa-00251296/file/ajp-jp4199202C225.pdf |archive-date=2020-05-09 |url-status=live}} European Workshop on Glasses and Gels.</ref> [[sugar glass]],<ref>{{Cite book|url=https://books.google.com/books?id=uk66BAAAQBAJ&pg=PA38|title=Candy Bites: The Science of Sweets|last1=Hartel|first1=Richard W.|last2=Hartel|first2=AnnaKate|year=2014|page=38|publisher=Springer Science & Business Media|isbn=978-1-4614-9383-9}}</ref> or Ca<sub>0.4</sub>K<sub>0.6</sub>(NO<sub>3</sub>)<sub>1.4</sub>.<ref>{{cite journal|author=Charbel Tengroth|title=Structure of Ca0.4K0.6(NO3)1.4 from the glass to the liquid state|journal=Phys. Rev. B|volume=64|page=224207|year=2001|issue=22|doi=10.1103/PhysRevB.64.224207|bibcode=2001PhRvB..64v4207T}}</ref> Glass electrolytes in the form of Ba-doped Li-glass and Ba-doped Na-glass have been proposed as solutions to problems identified with organic liquid electrolytes used in modern lithium-ion battery cells.<ref>{{cite web|url=http://fortune.com/2017/03/05/lithium-ion-battery-goodenough/|title=Lithium-Ion Pioneer Introduces New Battery That's Three Times Better|website=Fortune|access-date=2017-05-06|url-status=live|archive-url=https://web.archive.org/web/20170409193506/http://fortune.com/2017/03/05/lithium-ion-battery-goodenough/|archive-date=9 April 2017}}</ref>

== Production ==
{{Main|Glass production|Float glass|Glassblowing}}
{{Missing information|section|manual glassworking (glassblowing, shapeforming, etc.)|date=May 2023}}

[[File:Float Glass Unloading.jpg|thumb|Robotised float glass unloading|alt=Industrial robots unloading float glass]]
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 melting furnace]]s. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.<ref name=ullmann />
After melting, homogenization and [[refining (glass)|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, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.<ref>{{cite web|url=http://www.pfg.co.za/about%20glass.htm |title=PFG Glass |publisher=Pfg.co.za |access-date=24 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20091106210357/http://www.pfg.co.za/about%20glass.htm |archive-date=6 November 2009}}</ref> [[Container glass]] for common bottles and jars is formed by [[Glass container production#Forming process|blowing and pressing]] methods.<ref>{{Cite book|url=https://books.google.com/books?id=Kbxv0oPJPK4C&pg=PA449|title=Code of Federal Regulations, Title 40,: Protection of Environment, Part 60 (Sections 60.1-end), Revised As of July 1, 2011|date=October 2011|publisher=Government Printing Office|isbn=978-0-16-088907-3}}</ref> This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance.<ref>{{Cite book|url=https://books.google.com/books?id=Pwvtj9jJd6wC&pg=PA552|title=Leachables and Extractables Handbook: Safety Evaluation, Qualification, and Best Practices Applied to Inhalation Drug Products|last1=Ball|first1=Douglas J.|last2=Norwood|first2=Daniel L.|last3=Stults|first3=Cheryl L. M.|last4=Nagao|first4=Lee M.|date=2012-01-24|publisher=John Wiley & Sons|isbn=978-0-470-17365-7|page=552|language=en}}</ref>

[[File:Skansen, Stockholm, Sweden (Unsplash).jpg|thumb|Glass blowing|alt=A red hot piece of glass being blown]]

Once the desired form is obtained, glass is usually [[annealing (glass)|annealed]] for the removal of stresses and to increase the glass's hardness and durability.<ref name="EB1911">{{Cite EB1911|wstitle=Glass|volume=12|pages=87–105}}</ref> Surface treatments, 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<ref>{{cite web|url= https://www.autoglassguru.com/blog/windshields-how-theyre-made/ |title= windshields how they are made|publisher=autoglassguru |access-date=2018-02-09}}</ref>), or optical properties ([[insulated glazing]], [[anti-reflective coating]]).<ref>{{cite web|url=https://www.lehigh.edu/imi/teched/GlassProcess/Lectures/Lecture10_Pantano_Surface_Treatments.pdf |archive-url=https://web.archive.org/web/20150909081808/http://www.lehigh.edu/imi/teched/GlassProcess/Lectures/Lecture10_Pantano_Surface_Treatments.pdf |archive-date=2015-09-09 |url-status=live|title=Glass Surface Treatments: Commercial Processes Used in Glass Manufacture|last=Pantano|first=Carlo}}</ref>

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 [[chemical]]s 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]] or [[alkaline earth metal]] oxides and hydroxides, or [[boron trioxide|boron oxide]]), or that the impurities are quantified (loss on ignition).<ref name="pnnl">{{cite web|url=http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html |title=Glass melting, Pacific Northwest National Laboratory |publisher=Depts.washington.edu |access-date=24 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100505144629/http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html |archive-date=5 May 2010}}</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 [[Chemically inert|inert]] ones, such as [[Aluminium hydroxide|aluminum hydroxide]] (Al(OH)<sub>3</sub>) over [[Aluminium oxide|alumina]] (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 [[homogeneous (chemistry)|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>{{cite web |last=Fluegel |first=Alexander |url=http://glassproperties.com/melting/ |title=Glass melting in the laboratory |publisher=Glassproperties.com |access-date=24 October 2009 |url-status=live |archive-url=https://web.archive.org/web/20090213120553/http://glassproperties.com/melting/ |archive-date=13 February 2009}}</ref>

=== Colour ===
{{Main|Glass coloring and color marking}}

Colour in glass may be obtained by addition of homogenously distributed electrically charged ions (or [[Transparent materials#Absorption of light in solids|colour centres]]). While ordinary [[soda–lime glass]] appears colourless in thin section, [[iron(II) oxide]] (FeO) impurities produce a green tint in thick sections.<ref name="Mukherjee13">{{cite book|last=Mukherjee|first=Swapna|title=The Science of Clays: Applications in Industry, Engineering, and Environment|publisher=Springer Science & Business Media|year=2013|pages=142|url=https://books.google.com/books?id=wALFBAAAQBAJ&pg=PA142|isbn=978-9-4007-6683-9}}</ref> [[Manganese dioxide]] (MnO<sub>2</sub>), which gives glass a purple colour, may be added to remove the green tint given by FeO.<ref>{{Cite book|title=CRC Handbook of Metal Etchants|last1=Walker|first1=Perrin|last2=Tarn|first2=William H.|publisher=CRC press|year=1990|page=798|isbn=978-1-4398-2253-1|url=https://books.google.com/books?id=-2ObmTZTq2QC&pg=PA798}}</ref> FeO and [[chromium(III) oxide]] (Cr<sub>2</sub>O<sub>3</sub>) additives are used in the production of green bottles.<ref name="Mukherjee13" /> [[Iron (III) oxide]], on the other-hand, produces yellow or yellow-brown glass.<ref name="Langhamer03">{{cite book|url=https://books.google.com/books?id=UwLCa_h3hTEC&pg=PA273|title=The Legend of Bohemian Glass: A Thousand Years of Glassmaking in the Heart of Europe|first=Antonín|last=Langhamer|pages=273|year=2003|publisher=Tigris|isbn=978-8-0860-6211-2}}</ref> Low concentrations (0.025 to 0.1%) of [[cobalt oxide]] (CoO) produces rich, deep blue [[cobalt glass]].<ref>{{cite web|url=https://intarch.ac.uk/journal/issue52/3/3.html|title=3. Glass, Colour and the Source of Cobalt|website=Internet Archaeology}}</ref> [[Chromium]] is a very powerful colourising agent, yielding dark green.<ref>[http://www.speclab.com/elements/chromium.htm Chemical Fact Sheet – Chromium] {{Webarchive|url=https://web.archive.org/web/20170815033017/http://www.speclab.com/elements/chromium.htm |date=2017-08-15 }} www.speclab.com.</ref>
[[Sulphur]] combined with [[carbon]] and iron salts produces amber glass ranging from yellowish to almost black.<ref>David M Issitt. [https://web.archive.org/web/20070305020112/http://1st.glassman.com/articles/glasscolouring.html Substances Used in the Making of Coloured Glass] 1st.glassman.com.</ref> A glass melt can also acquire an amber colour from a reducing combustion atmosphere.<ref>{{Cite book|url=https://books.google.com/books?id=-mwoDwAAQBAJ&pg=PA211|title=Introduction to Glass Science and Technology|last=Shelby|first=James E.|year=2007|page=211|publisher=Royal Society of Chemistry|isbn=978-1-84755-116-0}}</ref> [[Cadmium sulfide]] produces imperial [[red]], and combined with selenium can produce shades of yellow, orange, and red.<ref name="Mukherjee13" /><ref name="Langhamer03" /> The additive [[Copper(II) oxide]] (CuO) produces a [[turquoise (color)|turquoise]] colour in glass, in contrast to [[Copper(I) oxide]] (Cu<sub>2</sub>O) which gives a dull brown-red colour.<ref name="Nicholson00">{{cite book|url=https://books.google.com/books?id=Vj7A9jJrZP0C&pg=PA208|title=Ancient Egyptian Materials and Technology|first1=Paul T.|last1=Nicholson|first2=Ian|last2=Shaw|publisher=Cambridge University Press|year=2000|pages=208|isbn=978-0-521-45257-1}}</ref>

<!-- WORKING ON FINDING MORE SUITABLE REFERENCES FOR THIS
* [[Nickel]], depending on the concentration, produces blue, or [[violet (colour)|violet]], or even [[black]] glass. [[Lead crystal]] with added nickel acquires purplish colour. Nickel together with a small amount of cobalt was used for decolourizing of [[lead glass]]. -->
<gallery mode="nolines">
File:Bottle, wine (AM 1997.80.28-1).jpg|alt=A green glass bottle|[[Iron(II) oxide]] and [[chromium(III) oxide]] additives are often used in the production of green bottles.<ref name="Mukherjee13" />
File:Bristol.blue.glass.arp.750pix.jpg|alt=Several examples of deep blue glass|[[Cobalt oxide]] produces rich, [[cobalt glass|deep blue glass]], such as [[Bristol blue glass]].
File:Colour Eclipse, Danny Lane.jpg|alt=Three glass disks, with one coloured turquoise, another purple, and a third coloured red|Different oxide additives produce the different colours in glass: [[turquoise (color)|turquoise]] ([[Copper(II) oxide]]),<ref name="Nicholson00" /> purple ([[Manganese dioxide]]),<ref name="Mukherjee13" /> and red ([[Cadmium sulfide]]).<ref name="Mukherjee13" />
File:Chinese snuff bottle, Qing dynasty, glass bottle with amber stopper, Honolulu Museum of Art.JPG|Red glass bottle with yellow glass overlay
File:Glass ornaments.JPG|Amber-coloured glass
File:Glass garland bowl MET DP122006.jpg|Four-colour Roman glass bowl, manufactured {{Circa|1st century B.C.}}
</gallery>

== Uses ==
=== Architecture and windows ===
{{Main|Architectural glass|Window}}
Soda–lime [[Plate glass|sheet glass]] is typically used as transparent [[glazing in architecture|glazing]] material, typically as [[window]]s in external walls of buildings. Float or rolled sheet glass products is cut to size either by [[Scoring (industrial process)|scoring]] and snapping the material, [[laser cutting]], [[Water jet cutter|water jets]], or [[diamond blade]]d saw. The glass may be thermally or chemically [[Tempered glass|tempered]] (strengthened) for [[safety glass|safety]] and bent or curved during heating. Surface coatings may be added for specific functions such as scratch resistance, blocking specific wavelengths of light (e.g. [[infrared]] or [[ultraviolet]]), dirt-repellence (e.g. [[self-cleaning glass]]), or switchable [[Electrochromism|electrochromic]] coatings.<ref name="Weller12">{{cite book|url=https://books.google.com/books?id=NXXTAAAAQBAJ&q=glass%20in%20buildings&pg=PA1|title=Glass in Building: Principles, Applications, Examples|last1=Weller|first1=Bernhard|last2=Unnewehr|first2=Stefan|last3=Tasche|first3=Silke|last4=Härth|first4=Kristina|year=2012|pages=1–19|publisher=Walter de Gruyter|isbn=978-3-0346-1571-6}}</ref>

Structural glazing systems represent one of the most significant architectural innovations of modern times, where glass buildings now often dominate [[skyline]]s of many modern [[cities]].<ref name="glass-times">{{cite web|url=https://glasstimes.co.uk/featured-articles/the-rise-of-glass-buildings/ |title=The rise of glass buildings |work=Glass Times|date=9 January 2017 |access-date=2020-03-01}}</ref> These systems use stainless steel fittings countersunk into recesses in the corners of the glass panels allowing strengthened panes to appear unsupported creating a flush exterior.<ref name="glass-times" /> Structural glazing systems have their roots in iron and [[Conservatory (greenhouse)|glass conservatories]] of the nineteenth century<ref name="Patterson">{{cite book|title=Structural Glass Facades and Enclosures|last=Patterson|first=Mic|url=https://books.google.com/books?id=qsqi2jdH7ecC&pg=PT29|publisher=Jon Wiley & Sons|year=2011|pages=29|isbn=978-0-470-93185-1}}</ref>

=== Tableware ===
{{Main|Tableware|List of glassware}}
Glass is an essential component of tableware and is typically used for water, [[Beer glassware|beer]] and [[wine glass|wine]] drinking glasses.<ref name="glassalliance" /> Wine glasses are typically [[stemware]], i.e. goblets formed from a bowl, stem, and foot. Crystal or [[Lead glass|Lead crystal]] glass may be cut and polished to produce decorative drinking glasses with gleaming facets.<ref>{{cite journal|title=Lead, glass and the environment |first1=Michael|last1=Hynes|first2=Bo|last2=Jonson|year=1997|journal=Chemical Society Reviews|volume=26|issue=2|page=145|doi=10.1039/CS9972600133}}</ref><ref>{{Cite web|url=https://www.britannica.com/art/cut-glass|title=Cut glass &#124; decorative arts|website=Encyclopedia Britannica}}</ref> Other uses of glass in tableware include [[decanters]], [[jug]]s, [[Plate (dishware)|plates]], and [[bowl]]s.<ref name="glassalliance" />
<gallery mode="nolines">

File:Jubilee Campus MMB «62 Melton Hall Christmas Dinner.jpg|Wine glasses and other glass tableware
File:British dimpled glass pint jug with ale.jpg|Dimpled glass beer pint jug
File:Crystal glass.jpg|[[Cut glass|lead crystal cut glass]]
File:Decanter and Stopper LACMA 56.35.29a-b.jpg|A glass [[decanter]] and [[Bung|stopper]]
</gallery>

=== Packaging ===
{{Main|Container glass}}
The inert and impermeable nature of glass makes it a stable and widely used material for food and drink packaging as [[glass bottle]]s and [[jar]]s. Most [[container glass]] is [[soda–lime glass]], produced by [[Glass production#Forming process|blowing and pressing]] techniques. Container glass has a lower [[magnesium oxide]] and [[sodium oxide]] content than flat glass, and a higher [[silica]], [[calcium oxide]], and [[aluminum oxide]] content.<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> Its higher content of water-insoluble oxides imparts slightly higher [[chemical durability]] against water, which is advantageous for storing beverages and food. Glass packaging is sustainable, readily recycled, reusable and refillable.<ref>{{Cite web|url=https://feve.org/about-glass/|title=Why choose Glass?|website=FEVE}}</ref>

For electronics applications, glass can be used as a substrate in the manufacture of [[integrated passive devices]], [[thin-film bulk acoustic resonator]]s, and as a [[hermetic seal]]ing material in device packaging,<ref>{{cite book |last1=Sun |first1=P. |last2=et |first2=al. |title=2018 19th International Conference on Electronic Packaging Technology (ICEPT) |chapter=Design and Fabrication of Glass-based Integrated Passive Devices |doi=10.1109/ICEPT.2018.8480458 |year=2018 |pages=59–63 |isbn=978-1-5386-6386-8 |s2cid=52935909 }}</ref><ref>{{cite book |last1=Letz |first1=M. |last2=et |first2=al. |title=2018 IEEE 68th Electronic Components and Technology Conference (ECTC) |chapter=Glass in Electronic Packaging and Integration: High Q Inductances for 2.35 GHZ Impedance Matching in 0.05 mm Thin Glass Substrates |doi=10.1109/ECTC.2018.00167 |year=2018 |pages=1089–1096 |isbn=978-1-5386-4999-2 |s2cid=51972637 }}</ref> including very thin solely glass based encapsulation of integrated circuits and other semiconductors in high manufacturing volumes.<ref>{{cite book |last1=Lundén |first1=H. |last2=et |first2=al. |title=Proceedings of the 5th Electronics System-integration Technology Conference (ESTC) |chapter=Novel glass welding technique for hermetic encapsulation |year=2014 |doi=10.1109/ESTC.2014.6962719 |pages=1–4 |isbn=978-1-4799-4026-4 |s2cid=9980556 }}</ref>

=== Laboratories ===
{{Main|Laboratory glassware}}
Glass is an important material in scientific laboratories for the manufacture of experimental apparatus because it is relatively cheap, readily formed into required shapes for experiment, easy to keep clean, can withstand heat and cold treatment, is generally non-reactive with many [[reagent]]s, and its transparency allows for the observation of chemical reactions and processes.<ref name="Zumdahl">{{cite book|url=https://books.google.com/books?id=5qgZBQAAQBAJ&q=laboratory%20glassware&pg=PT10|last=Zumdahl|first=Steven|year=2013|publisher=Cengage Learning|title=Lab Manual|pages=ix–xv|isbn=978-1-285-69235-7}}</ref><ref>{{Cite web|url=https://americanhistory.si.edu/science-under-glass|title=Science Under Glass|date=29 July 2015|website=National Museum of American History}}</ref> [[Laboratory glassware]] applications include [[Laboratory flask|flasks]], [[petri dish]]es, [[test tube]]s, [[pipette]]s, [[graduated cylinder]]s, glass lined metallic containers for chemical processing, [[fractionation column]]s, glass pipes, [[Schlenk line]]s, [[Gauge (instrument)|gauges]], and [[thermometer]]s.<ref name="BASUDEB">{{cite book|url=https://books.google.com/books?id=T838DAAAQBAJ&q=uses%20of%20glass&pg=PA5|title=Functional Glasses and Glass-Ceramics: Processing, Properties and Applications|pages=3–5|year=2017|last=Basudeb|first=Karmakar|publisher=Butterworth-Heinemann|isbn=978-0-12-805207-5}}</ref><ref name="Zumdahl" /> Although most standard laboratory glassware has been mass-produced since the 1920s, scientists still employ skilled [[glassblower]]s to manufacture bespoke glass apparatus for their experimental requirements.<ref>{{cite web|url=https://americanhistory.si.edu/science-under-glass/scientific-glassblowing |title=Scientific Glassblowing &#124; National Museum of American History |publisher=Americanhistory.si.edu |date=2012-12-17 |access-date=2020-03-04}}</ref>
<gallery mode="nolines">

File:Vigreux column lab.jpg|A Vigreux [[Fractionating column|column]] in a laboratory setup
File:Double vac line front view.jpg|A [[Schlenk line]] with four ports
File:Different types of graduated cylinder- 10ml, 25ml, 50ml and 100 ml graduated cylinder.jpg|[[Graduated cylinder]]s
File:250 mL Erlenmeyer flask.jpg|Erlenmeyer [[Laboratory flask|flask]]
</gallery>

=== Optics ===
Glass is a ubiquitous material in [[optics]] by virtue of its ability to [[Refraction|refract]], [[Reflection (physics)|reflect]], and [[Transmittance|transmit]] light. These and other optical properties can be controlled by varying chemical compositions, thermal treatment, and manufacturing techniques. The many applications of glass in optics includes [[glasses]] for eyesight correction, imaging optics (e.g. [[lens]]es and [[mirror]]s in [[telescope]]s, [[microscope]]s, and [[camera]]s), [[fibre optics]] in [[telecommunications]] technology, and [[Photonic integrated circuit|integrated optics]]. [[Microlens]]es and [[gradient-index optics]] (where the [[refractive index]] is non-uniform) find application in e.g. reading [[optical disc]]s, [[laser printer]]s, [[photocopier]]s, and [[laser diode]]s.<ref name=Bach12 />

=== Art ===
{{Main|Studio glass|Art glass|Glass art}}
Glass as art dates to least 1300 BC shown as an example of natural glass found in Tutankhamun's pectoral,<ref name="BBC">[http://news.bbc.co.uk/2/hi/science/nature/5196362.stm Tut's gem hints at space impact], [[BBC News]], July 19, 2006.</ref> which also contained [[vitreous enamel]], that is to say, melted coloured glass used on a metal backing. [[Enamelled glass]], the decoration of glass vessels with coloured glass paints, has existed since 1300 BC,<ref>[https://www.ganoksin.com/article/earliest-cloisonne-enamels/ The Earliest Cloisonné Enamels]</ref> and was prominent in the early 20th century with [[Art Nouveau glass]] and that of the [[House of Fabergé]] in St. Petersburg, Russia. Both techniques were used in [[stained glass]], which reached its height roughly from 1000 to 1550, before a revival in the 19th century.

The 19th century saw a revival in ancient glassmaking techniques including [[cameo glass]], achieved for the first time since the Roman Empire, initially mostly for pieces in a [[neoclassicism|neo-classical]] style. The [[Art Nouveau]] movement made great use of glass, with [[René Lalique]], [[Émile Gallé]], and [[Daum (studio)|Daum of Nancy]] in the first French wave of the movement, producing coloured vases and similar pieces, often in cameo glass or in [[lustre glass]] techniques.<ref>{{cite book |title=The Art of Glass: Art Nouveau to Art Deco |last=Arwas |first=Victor |year=1996 |pages=1–54 |url=https://books.google.com/books?id=bZsuJ90UAtIC&pg=PP1 |isbn=978-1-901092-00-4}}</ref>

[[Louis Comfort Tiffany]] in America specialised in [[stained glass]], both secular and religious, in panels and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as [[Waterford Crystal|Waterford]] and [[Lalique]]. Small studios may hand-produce glass artworks. Techniques for producing glass art include [[glassblowing|blowing]], kiln-casting, fusing, slumping, [[pâte de verre]], flame-working, hot-sculpting and cold-working. Cold work includes traditional stained glass work and other methods of shaping glass at room temperature. Objects made out of glass include vessels, [[paperweight collecting|paperweights]], [[marbles]], [[bead]]s, sculptures and [[installation art]].<ref name="V&A A-Z">{{cite web |title=A-Z of glass |url=https://www.vam.ac.uk/articles/a-z-of-glass |publisher=Victoria and Albert Museum |access-date=9 March 2020}}</ref>

<gallery mode="nolines">
Image:Portland Vase BM Gem4036 n5.jpg|The [[Portland Vase]], Roman [[cameo glass]], about 5–25 AD
File:Medallion St Demetrios Louvre OA6457.jpg|Byzantine [[cloisonné enamel]] plaque of [[St Demetrios]], c. 1100, using the ''senkschmelz'' or "sunk" technique
File:Gallé, nancy, vaso clematis, 1890-1900.JPG|[[Émile Gallé]], Marquetry glass vase with clematis flowers (1890–1900)
File:Vase (Perruches) by René Jules Lalique, 1922, blown four mold glass - Cincinnati Art Museum - DSC04355.JPG|Glass vase by [[art nouveau]] artist [[René Lalique]]
File:Clara driscoll per tiffany studios, lampada laburnum, 1910 ca. 02.jpg|[[Clara Driscoll (glass designer)|Clara Driscoll]] [[Tiffany lamp]], [[laburnum]] pattern, c. 1910 
File:Glass.sculpture.kewgardens.london.arp.jpg|A glass sculpture by [[Dale Chihuly]], "The Sun" at the "Gardens of Glass" exhibition in Kew Gardens, London
</gallery>

== See also ==
{{div col}}
* [[Fire glass]]
* [[Flexible glass]]
* [[Kimberley points]]
* [[Prince Rupert's drop]]
* [[Smart glass]]
{{div col end}}

== References ==
{{reflist|colwidth=30em}}

== External links ==
{{Sister project links| wikt=no | commons=Category:Glass | b=no | n=no | q=Glass | s=no | v=yes | voy=no | species=no | d=no}}
* {{cite EB1911|wstitle=Glass |volume=12 |short=x}}
<!-- DO NOT ADD COMMERCIAL LINKS TO THIS LIST-->
* [http://www.civilisations.ca/cmc/exhibitions/hist/verre/vemak01e.shtml The Story of Glass Making in Canada] from The Canadian Museum of Civilization.
* [https://books.google.com/books?id=pCEDAAAAMBAJ&pg=RA1-PA61 "How Your Glass Ware Is Made"] by George W. Waltz, February 1951, ''[[Popular Science]]''.
* [http://www.cmog.org/research/all-about-glass All About Glass] from the Corning Museum of Glass: a collection of articles, multimedia, and virtual books all about glass, including the [http://www.cmog.org/research/glass-dictionary Glass Dictionary].
* [http://www.glass.org/ National Glass Association]—The largest trade association representing the flat (architectural), auto glass, and window & door industries
<!-- DO NOT ADD COMMERCIAL LINKS TO THIS LIST-->

{{Glass science}}
{{Glass forming}}
{{Glass makers and brands}}
{{Authority control}}

[[Category:Glass| ]]
[[Category:Amorphous solids]]
[[Category:Dielectrics]]
[[Category:Materials]]
[[Category:Packaging materials]]
[[Category:Sculpture materials]]
[[Category:Windows]]