Glass is anamorphous (non-crystalline) solid. Because it is oftentransparent and chemically inert, glass has found widespread practical, technological, and decorative use inwindow panes,tableware, andoptics. Some common objects made of glass are named after the material, e.g., a"glass" for drinking, "glasses" for vision correction, and a "magnifying glass".

Glass is most often formed by rapid cooling (quenching) of themolten form. Some glasses such asvolcanic glass are naturally occurring, andobsidian has been used to make arrowheads and knives since theStone Age. Archaeological evidence suggests glassmaking dates back to at least 3600 BC inMesopotamia,Egypt, orSyria. The earliest known glass objects werebeads, perhaps created accidentally duringmetalworking or the production offaience, which is a form of pottery using lead glazes.

Due to its ease offormability into any shape, glass has been traditionally used for vessels, such asbowls,vases,bottles, jars and drinking glasses.Soda–lime glass, containing around 70%silica, accounts for around 90% of modern manufactured glass. Glass can be coloured by adding metal salts or painted and printed withvitreous enamels, leading to its use instained glass windows and otherglass art objects.

Therefractive,reflective andtransmission properties of glass make glass suitable for manufacturingoptical lenses,prisms, andoptoelectronics materials. Extrudedglass fibres have applications asoptical fibres in communications networks, thermal insulating material when matted asglass wool to trap air, or in glass-fibre reinforced plastic (fibreglass).

The standard definition of aglass (or vitreous solid) is a non-crystalline solid formed by rapid meltquenching.^[1][2][3][4] However, the term "glass" is often defined in a broader sense, to describe any non-crystalline (amorphous) solid that exhibits aglass transition when heated towards the liquid state.^[4][5]

Glass is anamorphous solid. Although the atomic-scale structure of glass shares characteristics of the structure of asupercooled liquid, glass exhibits all the mechanical properties of a solid.^[6][7][8] As in otheramorphous solids, the atomic structure of a glass lacks the long-range periodicity observed incrystalline solids. Due tochemical bonding constraints, glasses do possess a high degree of short-range order with respect to local atomicpolyhedra.^[9] The notion that glass flows to an appreciable extent over extended periods well below the glass transition temperature is not supported by empirical research or theoretical analysis (seeviscosity in solids). Though atomic motion at glass surfaces can be observed,^[10] and viscosity on the order of 10¹⁷–10¹⁸ 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.^[5][11]

For melt quenching, if the cooling is sufficiently rapid (relative to the characteristiccrystallization time) then crystallization is prevented and instead, the disordered atomic configuration of thesupercooled liquid is frozen into the solid state at T_g. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by therigidity theory.^[13] Generally, a glass exists in a structurallymetastable state with respect to itscrystalline form, although in certain circumstances, for example inatactic polymers, there is no crystalline analogue of the amorphous phase.^[14]

Glass is sometimes considered to be a liquid due to its lack of a first-orderphase transition^[7][15]where certainthermodynamicvariables such asvolume,entropy andenthalpy are discontinuous through the glass transition range. Theglass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as thethermal expansivity andheat capacity are discontinuous.^[2] 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.^[4][5]

Glass can form naturally from volcanic magma.Obsidian is a common volcanic glass with high silica (SiO₂) content formed when felsic lava extruded from a volcano cools rapidly.^[16]Impactite is a form of glass formed by the impact of ameteorite, whereMoldavite (found in central and eastern Europe), andLibyan desert glass (found in areas in the easternSahara, thedeserts of eastern Libya andwestern Egypt) are notable examples.^[17]Vitrification ofquartz can also occur whenlightning strikessand, forming hollow,branching rootlike structures calledfulgurites.^[18]Trinitite is a glassy residue formed from the desert floor sand at theTrinitynuclear bomb test site.^[19]Edeowie glass, found inSouth Australia, is proposed to originate fromPleistocene grassland fires,lightning strikes, orhypervelocity impact by one or severalasteroids orcomets.^[20]

•  
  A piece of volcanicobsidian glass
•  
  Moldavite, a natural glass formed bymeteorite impact, fromBesednice,Bohemia
•  
  Tubefulgurites
•  
  Trinitite, a glass made by theTrinity nuclear-weapon test
•  
  Libyan desert glass

Naturally occurringobsidian glass was used byStone Age societies as it fractures along very sharp edges, making it ideal for cutting tools and weapons.^[21][22]

Glassmaking dates back at least 6000 years, long before humans had discovered how tosmelt iron.^[21] Archaeological evidence suggests that the first true synthetic glass was made inLebanon and the coastal northSyria,Mesopotamia orancient Egypt.^[23][24] The earliest known glass objects, of the mid-third millennium BC, werebeads, perhaps initially created as accidental by-products ofmetalworking (slags) or during the production offaience, a pre-glassvitreous material made by a process similar toglazing.^[25]

Early glass was rarely transparent and often contained impurities and imperfections,^[21] and is technically faience rather than true glass, which did not appear until the 15th century BC.^[26] However, red-orange glass beads excavated from theIndus 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.^[27][28]

During theLate Bronze Age, there was a rapid growth inglassmaking technology inEgypt andWestern Asia.^[23] Archaeological finds from this period include coloured glassingots, vessels, and beads.^[23][29]

Much early glass production relied on grinding techniques borrowed fromstoneworking, such as grinding and carving glass in a cold state.^[30]

The termglass has its origins in the lateRoman Empire, in theRoman glass making centre atTrier (located in current-day Germany) where thelate-Latin termglesum originated, likely from aGermanic word for atransparent,lustrous substance.^[31] Glass objects have been recovered across the Roman Empire^[32] in domestic,funerary,^[33] and industrial contexts,^[34] as well as trade items in marketplaces in distant provinces.^[35][36] Examples ofRoman glass have been found outside of the formerRoman Empire inChina,^[37] theBaltics, theMiddle East, andIndia.^[38] The Romans perfectedcameo glass, produced byetching and carving through fused layers of different colours to produce a design in relief on the glass object.^[39]

Inpost-classical West Africa,Benin was a manufacturer of glass and glass beads.^[40]Glass was used extensively in Europe during theMiddle Ages.Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites.^[41] From the 10th century onwards, glass was employed instained glass windows of churches andcathedrals, with famous examples atChartres Cathedral and theBasilica of Saint-Denis. By the 14th century, architects were designing buildings with walls ofstained glass such asSainte-Chapelle, Paris, (1203–1248) and the East end ofGloucester Cathedral. With the change in architectural style during theRenaissance period in Europe, the use of large stained glass windows became much less prevalent,^[42] although stained glass had a major revival withGothic Revival architecture in the 19th century.^[43]

During the 13th century, the island ofMurano,Venice, became a centre for glass making, building on medieval techniques to produce colourful ornamental pieces in large quantities.^[39]Murano glass makers developed the exceptionally clear colourless glasscristallo, so called for its resemblance to natural crystal, which was extensively used for windows, mirrors, ships' lanterns, and lenses.^[21] In the 13th, 14th, and 15th centuries, enamelling andgilding on glass vessels were perfected in Egypt and Syria.^[44] 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 inEngland. In about 1675,George Ravenscroft inventedlead crystal glass, withcut glass becoming fashionable in the 18th century.^[39] Ornamental glass objects became an important art medium during theArt Nouveau period in the late 19th century.^[39]

Throughout the 20th century, newmass production techniques led to the widespread availability of glass in much larger amounts, making it practical as a building material and enabling new applications of glass.^[45] In the 1920s amould-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 asDepression glass.^[46] In the 1950s,Pilkington Bros.,England, developed thefloat glass process, producing high-quality distortion-free flat sheets of glass by floating on moltentin.^[21] Modern multi-story buildings are frequently constructed withcurtain walls made almost entirely of glass.^[47]Laminated glass has been widely applied to vehicles for windscreens.^[48] Optical glass for spectacles has been used since the Middle Ages.^[49] The production of lenses has become increasingly proficient, aidingastronomers^[50] as well as having other applications in medicine and science.^[51] Glass is also employed as the aperture cover in manysolar energy collectors.^[52]

In the 21st century, glass manufacturers have developed different brands ofchemically strengthened glass for widespread application intouchscreens forsmartphones,tablet computers, and many other types ofinformation appliances. These includeGorilla Glass, developed and manufactured byCorning,AGC Inc.'sDragontrail andSchott AG's Xensation.^[53][54][55]

Glass is in widespread use in optical systems due to its ability to refract, reflect, and transmit light followinggeometrical optics. The most common and oldest applications of glass in optics are aslenses,windows,mirrors, andprisms.^[56] The key optical propertiesrefractive index,dispersion, andtransmission, of glass are strongly dependent on chemical composition and, to a lesser degree, its thermal history.^[56] Optical glass typically has a refractive index of 1.4 to 2.4, and anAbbe number (which characterises dispersion) of 15 to 100.^[56] The refractive index may be modified by high-density (refractive index increases) or low-density (refractive index decreases) additives.^[57]

Glass transparency results from the absence ofgrain boundaries whichdiffusely scatter light in polycrystalline materials.^[58] 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 glassporcelain is produced.^[44][59] Although generally transparent to visible light, glasses may beopaque to otherwavelengths of light. While silicate glasses are generally opaque toinfrared wavelengths with a transmission cut-off at 4 μm, heavy-metalfluoride andchalcogenide glasses are transparent to infrared wavelengths of 7 to 18 μm.^[60] The addition of metallic oxides results in different coloured glasses as the metallic ions will absorb wavelengths of light corresponding to specific colours.^[60]

In the manufacturing process, glasses can be poured, formed, extruded and moulded into forms ranging from flat sheets to highly intricate shapes.^[61] The finished product is brittle but can belaminated ortempered to enhance durability.^[62][63] 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.^[21][64][65] Nevertheless, although usually highly resistant to chemical attack, glass will corrode or dissolve under some conditions.^[64][66] The materials that make up a particular glass composition affect how quickly the glass corrodes. Glasses containing a high proportion ofalkali oralkaline earth elements are more susceptible to corrosion than other glass compositions.^[67][68]

The density of glass varies with chemical composition with values ranging from 2.2 grams per cubic centimetre (2,200 kg/m³) forfused silica to 7.2 grams per cubic centimetre (7,200 kg/m³) for dense flint glass.^[69] Glass is stronger than most metals, with a theoreticaltensile strength for pure, flawless glass estimated at 14 to 35 gigapascals (2,000,000 to 5,100,000 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 14 to 175 megapascals (2,000 to 25,400 psi) in most commercial glasses.^[60] Several processes such astoughening can increase the strength of glass.^[70] Carefully drawn flawlessglass fibres can be produced with a strength of up to 11.5 gigapascals (1,670,000 psi).^[60]

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.^[71] 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-perfectfloat glass used today only became widespread in the 1960s).^[7]

A 2017 study computed the rate of flow of the medieval glass used inWestminster Abbey from the year 1268. The study found that the room temperature viscosity of this glass was roughly 10²⁴ Pa·s which is about 10¹⁶ 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 1nm per billion years, making it impossible to observe in a human timescale.^[72][73]

Silicon dioxide (SiO₂) is a common fundamental constituent of glass.Fused quartz is a glass made from chemically pure silica.^[68] It has very low thermal expansion and excellent resistance tothermal shock, being able to survive immersion in water while red hot, resists high temperatures (1000–1500 °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 theUV andIR 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.^[74] However, its high melting temperature (1723 °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.^[75]

Sodium carbonate (Na₂CO₃, "soda") is a common additive and acts to lower the glass-transition temperature. However,sodium silicate iswater-soluble, solime (CaO,calcium oxide, generally obtained fromlimestone), along withmagnesium oxide (MgO), andaluminium oxide (Al₂O₃), are commonly added to improve chemical durability. Soda–lime glasses (Na₂O) + lime (CaO) + magnesia (MgO) + alumina (Al₂O₃) account for over 75% of manufactured glass, containing about 70 to 74% silica by weight.^[68][76] Soda–lime–silicate glass is transparent, easily formed, and most suitable for window glass and tableware.^[77] However, it has a high thermal expansion and poor resistance to heat.^[77] Soda–lime glass is typically used forwindows,bottles,light bulbs, andjars.^[75]

Borosilicate glasses (e.g.Pyrex,Duran) typically contain 5–13%boron trioxide (B₂O₃).^[75] Borosilicate glasses have fairly lowcoefficients of thermal expansion (7740 Pyrex CTE is 3.25×10⁻⁶/°C^[78] as compared to about 9×10⁻⁶/°C for a typical soda–lime glass^[79]). They are, therefore, less subject tostress caused bythermal expansion and thus less vulnerable tocracking fromthermal shock. They are commonly used for e.g.labware,household cookware, and sealed beam carhead lamps.^[75]

The addition oflead(II) oxide into silicate glass lowers the melting point andviscosity of the melt.^[80] The high density of lead glass (silica + lead oxide (PbO) + potassium oxide (K₂O) + soda (Na₂O) + 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 morespecular reflection and increasedoptical dispersion.^[68][81] 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.^[74] Lead oxide also facilitates the 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 invitreous enamels andglass solders. The highionic radius of the Pb²⁺ 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 (10^8.5 vs 10^6.5 Ω⋅cm,DC at 250 °C).^[82]

Aluminosilicate glass typically contains 5–10%alumina (Al₂O₃). Aluminosilicate glass tends to be more difficult to melt and shape compared to borosilicate compositions but has excellent thermal resistance and durability.^[75] Aluminosilicate glass is extensively used forfibreglass,^[83] used for making glass-reinforced plastics (boats, fishing rods, etc.), top-of-stove cookware, and halogen bulb glass.^[74][75]

The addition ofbarium 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 itsradioactivity has been replaced bylanthanum oxide in modern eyeglasses.^[84] Iron can be incorporated into glass to absorbinfrared radiation, for example in heat-absorbing filters for movie projectors, whilecerium(IV) oxide can be used for glass that absorbsultraviolet wavelengths.^[85]Fluorine lowers thedielectric constant of glass. Fluorine is highlyelectronegative and lowers the polarizability of the material. Fluoride silicate glasses are used in the manufacture ofintegrated circuits as an insulator.^[86]

Glass-ceramic materials contain both non-crystalline glass andcrystallineceramic phases. They are formed by controlled nucleation and partial crystallisation of a base glass by heat treatment.^[87] Crystalline grains are often embedded within a non-crystalline intergranular phase ofgrain boundaries. Glass-ceramics exhibit advantageous thermal, chemical, biological, and dielectric properties as compared to metals or organic polymers.^[87]

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 negativethermal 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 ofglass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.^[88][87]

Fibreglass (also called glass fibre reinforced plastic, GRP) is acomposite material made by reinforcing a plasticresin withglass fibres. 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.^[89][90][91]Fibreglass has the properties of being lightweight and corrosion resistant and is a goodinsulator enabling its use asbuilding insulation material and for electronic housing for consumer products. Fibreglass was originally used in the United Kingdom and United States duringWorld War II to manufactureradomes. Uses of fibreglass include building and construction materials, boat hulls, car body parts, and aerospace composite materials.^[92][89][91]

Glass-fibre wool is an excellentthermal andsound insulation material, commonly used in buildings (e.g.attic andcavity wall insulation), and plumbing (e.g.pipe insulation), andsoundproofing.^[92] It is produced by forcing molten glass through a fine mesh bycentripetal 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.^[60]

Besides common silica-based glasses many otherinorganic andorganic materials may also form glasses, includingmetals,aluminates,phosphates,borates,chalcogenides,fluorides, germanates (glasses based onGeO₂), tellurites (glasses based on TeO₂), antimonates (glasses based on Sb₂O₃), arsenates (glasses based on As₂O₃), titanates (glasses based on TiO₂), tantalates (glasses based on Ta₂O₅),nitrates,carbonates,plastics,acrylic, and many other substances.^[5] Some of these glasses (e.g.Germanium dioxide (GeO₂, Germania), in many respects a structural analogue of silica,fluoride,aluminate,phosphate,borate, andchalcogenide glasses) have physicochemical properties useful for their application infibre-opticwaveguides in communication networks and other specialised technological applications.^[94][95]

Silica-free glasses may often have poor glass-forming tendencies. Novel techniques, including containerless processing byaerodynamic levitation (cooling the melt whilst it floats on a gas stream) orsplat quenching (pressing the melt between two metal anvils or rollers), may be used to increase the cooling rate or to reduce crystal nucleation triggers.^[96][97][98]

In the past, small batches ofamorphous metals 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.^[99][100]

Several alloys have been produced in layers with thicknesses exceeding 1 millimetre. These are known as bulk metallic glasses (BMG).Liquidmetal Technologies sells severalzirconium-based BMGs.

Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.^[101]

Experimental evidence indicates that the system Al-Fe-Si may undergo afirst-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 uniform spherical growth in all directions. Whilex-ray diffraction reveals the isotropic nature of q-glass, anucleation barrier exists implying an interfacial discontinuity (or internal surface) between the glass and melt phases.^[102][103]

Importantpolymer 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.^[104] Many polymerthermoplastics familiar to everyday use are glasses. For many applications, likeglass bottles oreyewear, polymer glasses (acrylic glass,polycarbonate orpolyethylene terephthalate) are a lighter alternative to traditional glass.^[105]

Molecular liquids,electrolytes,molten salts, andaqueous solutions are mixtures of differentmolecules orions that do not form a covalent network but interact only through weakvan der Waals forces or transienthydrogen bonds. 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.^[106][107] Examples include LiCl:RH₂O (a solution oflithium chloride salt and water molecules) in the composition range 4<R<8.^[108]sugar glass,^[109] or Ca_0.4K_0.6(NO₃)_1.4.^[110] 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.^[111]

Following theglass batch preparation and mixing, the raw materials are transported to the furnace.Soda–lime glass formass production is melted inglass-melting furnaces. Smaller-scale furnaces for speciality glasses include electric melters, pot furnaces, and day tanks.^[76]After melting, homogenization andrefining (removal of bubbles), the glass isformed. This may be achieved manually byglassblowing, which involves gathering a mass of hot semi-molten glass, inflating it into a bubble using a hollow blowpipe, and forming it into the required shape by blowing, swinging, rolling, or moulding. While hot, the glass can be worked using hand tools, cut with shears, and additional parts such as handles or feet attached by welding.^[112]Flat glass for windows and similar applications is formed by thefloat glass process, developed between 1953 and 1957 by SirAlastair 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.^[113]Container glass for common bottles and jars is formed byblowing and pressing methods.^[114] This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance.^[115]

Once the desired form is obtained, glass is usuallyannealed for the removal of stresses and to increase the glass's hardness and durability.^[116] Surface treatments, coatings orlamination may follow to improve the chemical durability (glass container coatings,glass container internal treatment), strength (toughened glass,bulletproof glass,windshields^[117]), or optical properties (insulated glazing,anti-reflective coating).^[118]

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 purechemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such asalkali oralkaline earth metal oxides and hydroxides, orboron oxide), or that the impurities are quantified (loss on ignition).^[119] Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g.,sodium selenite may be preferred over easily evaporatingselenium dioxide (SeO₂). Also, more readily reacting raw materials may be preferred over relativelyinert ones, such asaluminium hydroxide (Al(OH)₃) overalumina (Al₂O₃). Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glasshomogeneity is achieved by homogenizing the raw materials mixture (glass batch), stirring the melt, and crushing and re-melting the first melt. The obtained glass is usuallyannealed to prevent breakage during processing.^[119][120]

Colour in glass may be obtained by addition of homogenously distributed electrically charged ions (orcolour centres). While ordinarysoda–lime glass appears colourless in thin section,iron(II) oxide (FeO) impurities produce a green tint in thick sections.^[121]Manganese dioxide (MnO₂), which gives glass a purple colour, may be added to remove the green tint given by FeO.^[122] FeO andchromium(III) oxide (Cr₂O₃) additives are used in the production of green bottles.^[121]Iron (III) oxide, on the other-hand, produces yellow or yellow-brown glass.^[123] Low concentrations (0.025 to 0.1%) ofcobalt oxide (CoO) produce rich, deep bluecobalt glass.^[124]Chromium is a very powerful colouring agent, yielding dark green.^[125]Sulphur combined withcarbon and iron salts produces amber glass ranging from yellowish to almost black.^[126] A glass melt can also acquire an amber colour from a reducing combustion atmosphere.^[127]Cadmium sulfide produces imperialred, and combined with selenium can produce shades of yellow, orange, and red.^[121][123] Addition ofcopper(II) oxide (CuO) produces aturquoise colour in glass, in contrast tocopper(I) oxide (Cu₂O) which gives a dull red-brown colour.^[128]

•  
  Iron(II) oxide andchromium(III) oxide additives are often used in the production of green bottles.^[121]
•  
  Cobalt oxide produces rich,deep blue glass, such asBristol blue glass.
•  
  Different oxide additives produce the different colours in glass:turquoise (copper(II) oxide),^[128] purple (manganese dioxide),^[121] and red (cadmium sulfide).^[121]
•  
  Red glass bottle with yellow glass overlay
•  
  Amber-coloured glass
•  
  Four-colour Roman glass bowl, manufacturedc. 1st century B.C.

Soda–limesheet glass is typically used as a transparentglazing material, typically aswindows in external walls of buildings. Float or rolled sheet glass products are cut to size either byscoring and snapping the material,laser cutting,water jets, ordiamond-bladed saw. The glass may be thermally or chemicallytempered (strengthened) forsafety 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 orultraviolet), dirt-repellence (e.g.self-cleaning glass), or switchableelectrochromic coatings.^[129]

Structural glazing systems represent one of the most significant architectural innovations of modern times, where glass buildings now often dominate theskylines of many moderncities.^[130] 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.^[130] Structural glazing systems have their roots in iron andglass conservatories of the nineteenth century^[131]

Glass is an essential component of tableware and is typically used for water,beer andwine drinking glasses.^[51] Wine glasses are typicallystemware, i.e. goblets formed from a bowl, stem, and foot. Crystal orLead crystal glass may be cut and polished to produce decorative drinking glasses with gleaming facets.^[132][133] Other uses of glass in tableware includedecanters,jugs,plates, andbowls.^[51]

•  
  Wine glasses and other glass tableware
•  
  Dimpled glass beer pint jug
•  
  lead crystal cut glass
•  
  A glassdecanter andstopper

The inert and impermeable nature of glass makes it a stable and widely used material for food and drink packaging asglass bottles andjars. Mostcontainer glass issoda–lime glass, produced byblowing and pressing techniques. Container glass has a lowermagnesium oxide andsodium oxide content than flat glass, and a highersilica,calcium oxide, andaluminium oxide content.^[134] Its higher content of water-insoluble oxides imparts slightly higherchemical durability against water, which is advantageous for storing beverages and food. Glass packaging is sustainable, readily recycled, reusable and refillable.^[135]

For electronics applications, glass can be used as a substrate in the manufacture ofintegrated passive devices,thin-film bulk acoustic resonators, and as ahermetic sealing material in device packaging,^[136][137] including very thin solely glass based encapsulation of integrated circuits and other semiconductors in high manufacturing volumes.^[138]

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 manyreagents, and its transparency allows for the observation of chemical reactions and processes.^[139][140]Laboratory glassware applications includeflasks,Petri dishes,test tubes,pipettes,graduated cylinders, glass-lined metallic containers for chemical processing,fractionation columns, glass pipes,Schlenk lines,gauges, andthermometers.^[141][139] Although most standard laboratory glassware has been mass-produced since the 1920s, scientists still employ skilledglassblowers to manufacture bespoke glass apparatus for their experimental requirements.^[142]

•  
  A Vigreuxcolumn in a laboratory setup
•  
  ASchlenk line with four ports
•  
  Graduated cylinders
•  
  Erlenmeyerflask

Glass is a ubiquitous material inoptics because of its ability torefract,reflect, andtransmit 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 includeglasses for eyesight correction, imaging optics (e.g.lenses andmirrors intelescopes,microscopes, andcameras),fibre optics intelecommunications technology, andintegrated optics.Microlenses andgradient-index optics (where therefractive index is non-uniform) find application in e.g. readingoptical discs,laser printers,photocopiers, andlaser diodes.^[56]

The 19th century saw a revival in ancient glassmaking techniques includingcameo glass, achieved for the first time since the Roman Empire, initially mostly for pieces in aneo-classical style. TheArt Nouveau movement made great use of glass, withRené Lalique,Émile Gallé, andDaum of Nancy in the first French wave of the movement, producing coloured vases and similar pieces, often in cameo glass orlustre glass techniques.^[143]

Louis Comfort Tiffany in America specialised instained 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 asWaterford andLalique. Small studios may hand-produce glass artworks. Techniques for producing glass art includeblowing, 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,paperweights,marbles,beads, sculptures andinstallation art.^[144]

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  ThePortland Vase, Romancameo glass, about 5–25 AD
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  Byzantinecloisonné enamel plaque ofSt Demetrios, c. 1100, using thesenkschmelz or "sunk" technique
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  Émile Gallé, Marquetry glass vase with clematis flowers (1890–1900)
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  Glass vase byArt Nouveau artistRené Lalique
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  Clara DriscollTiffany lamp,laburnum pattern, c. 1910
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  A glass sculpture byDale Chihuly,The Sun, at the "Gardens of Glass" exhibition in Kew Gardens, London
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  TheGlass Flowers byLeopold and Rudolf Blaschka, exhibited at theHarvard Museum of Natural History

• "Glass" .Encyclopædia Britannica. Vol. 12 (11th ed.). 1911.
• The Story of Glass Making in Canada from The Canadian Museum of Civilization.
• "How Your Glass Ware Is Made" by George W. Waltz, February 1951,Popular Science.
• All About Glass from the Corning Museum of Glass: a collection of articles, multimedia, and virtual books all about glass, including theGlass Dictionary.