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glass: Wikis



, a natural glass formed by meteorite impact, from Besednice, Bohemia]]

in Wisley Garden, England, made from float glass]]


Glass generally refers to hard, brittle, transparent material, such as those used for windows, many bottles, or eyewear. Examples of such materials include, but are not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride. In the technical sense, glass is an inorganic product of fusion which has been cooled through the glass transition to a rigid condition without crystallizing.[1][2][3][4][5] Many glasses contain silica as their main component and glass former.[6]

In the scientific sense the term glass is often extended to all amorphous solids (and melts that easily form amorphous solids), including plastics, resins, or other silica-free amorphous solids. In addition, besides traditional melting techniques, any other means of preparation are considered, such as ion implantation, and the sol-gel method.[6] However, glass science and physics commonly includes only inorganic amorphous solids, while plastics and similar organics are covered by polymer science, biology and further scientific disciplines.

Glass plays an essential role in science and industry. The optical and physical properties of glass make it suitable for applications such as flat glass, container glass, optics and optoelectronics material, laboratory equipment, thermal insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber reinforced concrete), and art.

The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.[7]


Glass production

Glass ingredients

(silica) as main raw material for commercial glass production]]
(Kosta Glasbruk, Småland, 1742). In the middle is the mark from the glass blower's pipe.]]

Pure silica (SiO2) has a "glass melting point"— at a viscosity of 10 Pa·s (100 P)— of over 2300 °C (4200 °F). While pure silica can be made into glass for special applications (see fused quartz), other substances are added to common glass to simplify processing. One is sodium carbonate (Na2CO3), which lowers the melting point to about 1500 °C (2700 °F) in soda-lime glass; "soda" refers to the original source of sodium carbonate in the soda ash obtained from certain plants. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminum oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74 percent silica by weight and is called a soda-lime glass.[8] Soda-lime glasses account for about 90 percent of manufactured glass.

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

Two other common glass ingredients are calumite (an iron industry by-product) and "cullet" (recycled glass). The recycled glass saves on raw materials and energy. However, impurities in the cullet can lead to product and equipment failure.

Finally, fining agents such as sodium sulfate, sodium chloride, or antimony oxide are added to reduce the bubble content in the glass.[8] Glass batch calculation is the method by which the correct raw material mixture is determined to achieve the desired glass composition.

Contemporary glass production

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.[8]

After melting, homogenization and refining (removal of bubbles), the glass is 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.[9] Container glass for common bottles and jars is formed by blowing and pressing methods. Further glass forming techniques are summarized in the table Glass forming techniques.

Once the desired form is obtained, glass is usually annealed for the removal of stresses. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating).

Glassmaking in the laboratory

experiment for the study of nuclear waste disposal at Pacific Northwest National Laboratory.]]


New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali oxides and hydroxides, alkaline earth oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).[10] 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 SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass 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 annealed to prevent breakage during processing.[10][11]

In order to make glass from materials with poor glass forming tendencies, novel techniques are used to increase cooling rate, or reduce crystal nucleation triggers. Examples of these techniques include aerodynamic levitation (the melt is cooled whilst floating in a gas stream), splat quenching, (the melt is pressed between two metal anvils) and roller quenching (the melt is poured through rollers).

See also: Optical lens design, Fabrication and testing of optical components

Sol-gel science/technology

Silica-free glasses

Besides common silica-based glasses, many other inorganic and organic materials may also form glasses, including plastics (e.g., acrylic glass), carbon, metals, carbon dioxide (see below), phosphates, borates, chalcogenides, fluorides, germanates (glasses based on GeO2), 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 and many other substances.[6]

Some glasses that do not include silica as a major constituent may have physico-chemical properties useful for their application in fibre optics and other specialized technical applications. These include fluoride glasses (fluorozirconates, fluoroaluminates), aluminosilicates, phosphate glasses and chalcogenide glasses.

Under extremes of pressure and temperature solids may exhibit large structural and physical changes which can lead to polyamorphic phase transitions.[12] In 2006 Italian scientists created an amorphous phase of carbon dioxide using extreme pressure. The substance was named amorphous carbonia(a-CO2) and exhibits an atomic structure resembling that of Silica.[13]

Physics of glass

See also Physics of glass
Unsolved problems in physics: What is the nature of the transition between a fluid or regular solid and a glassy phase? What are the physical processes giving rise to the general properties of glasses?
arrangement of Oxygen (O) atoms around the Silicon (Si) atoms.]]

The standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching.[2][3][4][14] 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 the glass transition temperature Tg. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.[15] As in other amorphous solids, the atomic structure of a glass lacks any long range translational periodicity. However, due to chemical bonding characteristics glasses do possess a high degree of short-range order with respect to local atomic polyhedra.[16] It is deemed that the bonding structure of glasses, although disordered, has the same symmetry signature (Hausdorff-Besicovitch dimensionality) as for crystalline materials.[17]

Glass versus a supercooled liquid

Glass is generally classed as an amorphous solid rather than a liquid.[14][18] Glass displays all the mechanical properties of a solid. The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see viscosity of amorphous materials). From a more commonsense point of view, glass should be considered a solid since it is rigid according to everyday experience.[19]

Some people consider glass to be a liquid due to its lack of a first-order phase transition[18][20] where certain thermodynamic variables such as volume, entropy and enthalpy are continuous through the glass transition range. However, the glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous. Despite this, the equilibrium theory of phase transformations in solids does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.[4]

Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature.[21] A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion becomes impossible, explaining why glasses and crystalline materials are hard.

Behavior of antique glass

The observation that old windows are often thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a matter of centuries. It is then assumed that the glass was once uniform, but has flowed to its new shape, which is a property of liquid.[22] In actuality, the likely reason for this is that when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not, however, absolutely flat; the edges of the disk became thicker as the glass spun. When actually installed in a window frame, the glass would be placed thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window.[23] Occasionally such glass has been found thinner side down or thicker on either side of the window's edge, as would be caused by carelessness at the time of installation.

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

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

  • Writing in the American Journal of Physics, physicist Edgar D. Zanotto states "...the predicted relaxation time for GeO2 at room temperature is 1032 years. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer."[24] (1032 years is much longer than the estimated age of the Universe.)
  • If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more — but this is not observed. Similarly, prehistoric obsidian blades should have lost their edge; this is not observed either (although obsidian may have a different viscosity from window glass).[18]
  • If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes. Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed.[18]
  • There are many examples of centuries-old glass shelving which has not bent, even though it is under much higher stress from gravitational loads than vertical window glass.

Some glasses have a glass transition temperature close to or below room temperature. The behavior of a material that has a glass transition close to room temperature depends upon the timescale during which the material is manipulated. If the material is hit it may break like a solid glass, but if the material is left on a table for a week it may flow like a liquid. This simply means that for the fast timescale its transition temperature is above room temperature, but for the slow one it is below. The shift in temperature with timescale is not very large however, as indicated by the transition of polypropylene glycol of −72°C and −71°C over different timescales.[15] To observe window glass flowing as liquid at room temperature we would have to wait a much longer time than any human can exist. Therefore it is safe to consider a glass a solid far enough below its transition temperature: Cathedral glass does not flow because its glass transition temperature is many hundreds of degrees above room temperature. Close to this temperature there are interesting time-dependent properties. One of these is known as aging. Many polymers that we use in daily life such as rubber, polystyrene and polypropylene are in a glassy state but they are not too far below their glass transition temperature. Their mechanical properties may well change over time and this is serious concern when applying these materials in construction.

Physical properties

The following table lists some physical properties of common glasses. Unless otherwise stated, the technical glass compositions and many experimentally determined properties are taken from one large study.[25] Unless stated otherwise, the properties of fused silica (quartz glass) and germania glass are derived from the SciGlass glass database by forming the arithmetic mean of all the experimental values from different authors (in general more than 10 independent sources for quartz glass and Tg of germanium oxide glass). Those values marked in italic font have been interpolated from similar glass compositions (see Calculation of glass properties) due to the lack of experimental data.

Properties Soda-lime glass (for containers)[26] Borosilicate (low expansion, similar to Pyrex, Duran) Glass wool (for thermal insulation) Special optical glass (similar to
Lead crystal)
Fused silica Germania glass Germanium selenide glass
74 SiO2, 13 Na2O, 10.5 CaO, 1.3 Al2O3, 0.3 K2O, 0.2 SO3, 0.2 MgO, 0.01 TiO2, 0.04 Fe2O3 81 SiO2, 12.5 B2O3, 4 Na2O, 2.2 Al2O3, 0.02 CaO, 0.06 K2O 63 SiO2, 16 Na2O, 8 CaO, 3.3 B2O3, 5 Al2O3, 3.5 MgO, 0.8 K2O, 0.3 Fe2O3, 0.2 SO3 41.2 SiO2, 34.1 PbO, 12.4 BaO, 6.3 ZnO, 3.0 K2O, 2.5 CaO, 0.35 Sb2O3, 0.2 As2O3 SiO2 GeO2 GeSe2
log(η, Pa·s) = A +
B / (T in °C − To)
A = -2.309
B = 3922
To = 291
A = -2.834
B = 6668
To = 108
A = -2.323
B = 3232
To = 318
A = -35.59
B = 60930
To = −741
A = -7.766
B = 27913
To = −271.7
A = -11.044
B = 30979
To = −837
Glass transition
temperature, Tg, °C
573 536 551 ~540 1140 526 ± 27[27][28][29] 395 [30]
Coefficient of
thermal expansion,
ppm/K, ~100–300°C
9 3.5 10 7 0.55 7.3
at 20°C, [g/cm3], x1000 to get [kg/m3]
2.52 2.235 2.550 3.86 2.203 3.65 [31] 4.16 [30]
Refractive index nD[32] at 20°C 1.518 1.473 1.531 1.650 1.459 1.608 1.7
Dispersion at 20°C,
104×(nF − nC)[32]
86.7 72.3 89.5 169 67.8 146
Young's modulus
at 20°C, GPa
72 65 75 67 72 43.3 [33]
Shear modulus
at 20°C, GPa
29.8 28.2 26.8 31.3
temperature, °C
1040 1070[34] 1715 1115
capacity at 20°C,
49 50 50 51 44 52
Surface tension,
at ~1300°C, mJ/m2
315 370 290
Chemical durability,
Hydrolytic class,
after ISO 719[35]
3 1 3


Color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as in photochromic glasses).[6] Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt%[25] produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr2O3 additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black.[36] Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide.

Optical waveguides

rod, illustrating the total internal reflection of light in a multimode optical fiber.]]

Optically transparent materials focus on the response of a material to incoming light waves of a range of wavelengths. Frequency selective optical filters can be utilized to alter or enhance the brightness and contrast of a digital image. Guided light wave transmission via frequency selective waveguides involves the emerging field of fiber optics and the ability of certain glassy compositions as a transmission medium for a range of frequencies simultaneously (multimode optical fiber) with little or no interference between competing wavelengths or frequencies. This resonant mode of energy and data transmission via electromagnetic (light) wave propagation, though low powered, is relatively lossless.

An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The index of refraction is a way of measuring the speed of light in a material. (Note: The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in a given medium. (The index of refraction of a vacuum is therefore equal to 1, by definition). The larger the index of refraction, the more slowly light travels in that medium. Typical values for core and cladding of an optical fiber are 1.48 and 1.46, respectively.

When light traveling in a dense medium hits a boundary at a steep angle, the light will be completely reflected. This effect is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles will be propagated. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding.

Optical waveguides are used as components in integrated optical circuits (e.g. light-emitting diodes, LEDs) or as the transmission medium in local and long haul optical communication systems. Also of value to the emerging materials scientist is the sensitivity of materials to thermal radiation in the infrared (IR) portion of the EM spectrum. This infrared homing (or "heat-seeking") capability is responsible for such diverse optical phenomena as "night vision" and IR luminescence.


See also: Category:Glass history

, USA]]

from the 4th century A.D.]]

Naturally occurring glass, especially obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Old Kingdom Egypt.[37] Due to Egypt's favorable environment for preservation, the majority of well-studied early glass is found in Egypt, although some of this is likely to have been imported. The earliest known glass objects, of the mid third millennium BC, were beads, perhaps initially created as accidental by-products of metal-working slags or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.[38]

During the Late Bronze Age in Egypt and Western Asia there was an explosion in glass-making technology. Archaeological finds from this period include colored glass ingots, vessels (often colored and shaped in imitation of highly prized wares of semi-precious stones) and the ubiquitous beads. The alkali of Syrian and Egyptian glass was soda ash, sodium carbonate, which can be extracted from the ashes of many plants, notably halophile seashore plants: (see saltwort). The earliest vessels were 'core-wound', produced by winding a ductile rope of glass round a shaped core of sand and clay over a metal rod, then fusing it with repeated reheatings. Threads of thin glass of different colors made with admixtures of oxides were subsequently wound around these to create patterns, which could be drawn into festoons by using metal raking tools. The vessel would then be rolled flat ('marvered') on a slab in order to press the decorative threads into its body. Handles and feet were applied separately. The rod was subsequently allowed to cool as the glass slowly annealed and was eventually removed from the center of the vessel, after which the core material was scraped out. Glass shapes for inlays were also often created in moulds. Much early glass production, however, relied on grinding techniques borrowed from stone working. This meant that the glass was ground and carved in a cold state.

By the 15th century BC extensive glass production was occurring in Western Asia and Egypt. It is thought the techniques and recipes required for the initial fusing of glass from raw materials was a closely guarded technological secret reserved for the large palace industries of powerful states. Glass workers in other areas therefore relied on imports of pre-formed glass, often in the form of cast ingots such as those found on the Ulu Burun shipwreck off the coast of Turkey.

Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilisations seem to have brought glass-making to a halt. It picked up again in its former sites, in Syria and Cyprus, in the ninth century BC, when the techniques for making colorless glass were discovered. The first glassmaking "manual" dates back to ca. 650 BC. Instructions on how to make glass are contained in cuneiform tablets discovered in the library of the Assyrian king Ashurbanipal. In Egypt glass-making did not revive until it was reintroduced in Ptolemaic Alexandria. Core-formed vessels and beads were still widely produced, but other techniques came to the fore with experimentation and technological advancements. During the Hellenistic period many new techniques of glass production were introduced and glass began to be used to make larger pieces, notably table wares. Techniques developed during this period include 'slumping' viscous (but not fully molten) glass over a mould in order to form a dish and 'millefiori' (meaning 'thousand flowers') technique, where canes of multi-colored glass were sliced and the slices arranged together and fused in a mould to create a mosaic-like effect. It was also during this period that colorless or decolored glass began to be prized and methods for achieving this effect were investigated more fully.[7]

According to Pliny the Elder, Phoenician traders were the first to stumble upon glass manufacturing techniques at the site of the Belus River. Georgius Agricola, in De re metallica, reported a traditional serendipitous "discovery" tale of familiar type:

"The tradition is that a merchant ship laden with nitrum being moored at this place, the merchants were preparing their meal on the beach, and not having stones to prop up their pots, they used lumps of nitrum from the ship, which fused and mixed with the sands of the shore, and there flowed streams of a new translucent liquid, and thus was the origin of glass."[39]

This account is more a reflection of Roman experience of glass production, however, as white silica sand from this area was used in the production of Roman glass due to its low impurity levels.

During the first century BC glass blowing was discovered on the Syro-Palestinian coast, revolutionising the industry and laying the way for the explosion of glass production that occurred throughout the Roman world. It was the Romans who began to use glass for architectural purposes, with the discovery of clear glass (through the introduction of manganese oxide), in Alexandria ca. AD 100. Cast glass windows, albeit with poor optical qualities, thus began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii. Over the next 1,000 years glass making and working continued and spread through southern Europe and beyond.

South Asia

Indigenous development of glass technology in South Asia may have begun in 1730 BC.[40] Evidence of this culture includes a red-brown glass bead along with a hoard of beads dating to 1730 BC, making it the earliest attested glass from the Indus Valley locations.[40] Glass discovered from later sites dating from 600–300 BC displays common color.[40]

Chalcolithic evidence of glass has been found in Hastinapur, India.[41] Some of the texts which mention glass in India are the Shatapatha Brahmana and Vinaya Pitaka.[41] However, the first unmistakable evidence in large quantities, dating from the 3rd century BC, has been uncovered from the archaeological site in Taxila, Pakistan.[41]

By the beginning of the Common Era, glass was being used for ornaments and casing in South Asia.[41] Contact with the Greco-Roman world added newer techniques, and Indians artisans mastered several techniques of glass molding, decorating and coloring by the early centuries of the Common Era.[41] Satavahana period of India further reveals short cylinders of composite glass, including those displaying a lemon yellow matrix covered with green glass.[42]


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

Anglo-Saxon world

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

Islamic world

The Arab poet al-Buhturi (820–897) described the clarity of such glass, "Its color hides the glass as if it is standing in it without a container."[43]

Stained glass was also first produced by Muslim architects in Southwest Asia using colored glass rather than stone.[citation needed] In the 8th century, the Arab chemist Jabir ibn Hayyan (Geber) scientifically described 46 original recipes for producing colored glass in Kitab al-Durra al-Maknuna (The Book of the Hidden Pearl), in addition to 12 recipes inserted by al-Marrakishi in a later edition of the book.[44]

The parabolic mirror was first described by Ibn Sahl in his On the Burning Instruments in the 10th century, and later described again in Ibn al-Haytham's On Burning Mirrors and Book of Optics (1021).[45] By the 11th century, clear glass mirrors were being produced in Islamic Spain. The first glass factories were also built by Muslim craftsmen in the Islamic world.[citation needed] The first glass factories in Christian Europe were later built in the 11th century by Muslim Egyptian craftsmen in Corinth, Greece.[46]

Medieval Europe

Glass objects from the 7th and 8th centuries have been found on the island of Torcello near Venice. These form an important link between Roman times and the later importance of that city in the production of the material. Around 1000 AD, an important technical breakthrough was made in Northern Europe when soda glass, produced from white pebbles and burnt vegetation was replaced by glass made from a much more readily available material: potash obtained from wood ashes. From this point on, northern glass differed significantly from that made in the Mediterranean area, where soda remained in common use.[47]

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

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

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

Late medieval Northern Europe

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

Murano glassmaking

The center for glassmaking from the 14th century was the island of Murano, which developed many new techniques and became the center of a lucrative export trade in dinnerware, mirrors, and other luxury items. What made Venetian Murano glass significantly different was that the local quartz pebbles were almost pure silica, and were ground into a fine clear sand that was combined with soda ash obtained from the Levant, for which the Venetians held the sole monopoly. The clearest and finest glass is tinted in two ways: firstly, a small or large amount of a natural coloring agent is ground and melted with the glass. Many of these coloring agents still exist today; for a list of coloring agents, see below. Black glass was called obsidianus after obsidian stone. A second method is apparently to produce a black glass which, when held to the light, will show the true color that this glass will give to another glass when used as a dye. [48]

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

Glass art

being created at the Reijmyre glassworks, Sweden]]
with items inside the glass, Corning Museum of Glass]]

Beginning in the late 20th century, glass started to become highly collectible as art. Works of art in glass can be seen in a variety of museums, including the Chrysler Museum, the Museum of Glass in Tacoma, the Metropolitan Museum of Art, the Toledo Museum of Art, and Corning Museum of Glass, in Corning, NY, which houses the world's largest collection of glass art and history, with more than 45,000 objects in its collection.[49]

Several of the most common techniques for producing glass art include: blowing, kiln-casting, fusing, slumping, pate-de-verre, flame-working, hot-sculpting and cold-working. Cold work includes traditional stained glass work as well as other methods of shaping glass at room temperature. Glass can also be cut with a diamond saw, or copper wheels embedded with abrasives, and polished to give gleaming facets; the technique used in creating Waterford crystal [50]. Art is sometimes etched into glass via the use of acid, caustic, or abrasive substances. Traditionally this was done after the glass was blown or cast. In the 1920s a new mould-etch process was invented, in which art was etched directly into the mould, so that each cast piece emerged from the mould with the image already on the surface of the glass. This reduced manufacturing costs and, combined with a wider use of colored glass, led to cheap glassware in the 1930s, which later became known as Depression glass[51]. As the types of acids used in this process are extremely hazardous, abrasive methods have gained popularity.

Objects made out of glass include not only traditional objects such as vessels (bowls, vases, bottles, and other containers), paperweights, marbles, beads, but an endless range of sculpture and installation art as well. Colored glass is often used, though sometimes the glass is painted, innumerable examples exist of the use of stained glass.

The Harvard Museum of Natural History has a collection of extremely detailed models of flowers made of painted glass. These were lampworked by Leopold Blaschka and his son Rudolph, who never revealed the method he used to make them. The Blaschka Glass Flowers are still an inspiration to glassblowers today. [52]

See also


  1. ^ ASTM definition of glass from 1945; also: DIN 1259, Glas – Begriffe für Glasarten und Glasgruppen, September 1986
  2. ^ a b Zallen, R. (1983). The Physics of Amorphous Solids. New York: John Wiley. 
  3. ^ a b Cusack, N. E. (1987). The physics of structurally disordered matter: an introduction. Adam Hilger in association with the University of Sussex press. 
  4. ^ a b c Elliot, S. R. (1984). Physics of Amorphous Materials. Longman group ltd. 
  5. ^ Horst Scholze (1991). Glass – Nature, Structure, and Properties. Springer. ISBN 0-387-97396-6. 
  6. ^ a b c d Werner Vogel (1994). Glass Chemistry (2 ed.). Springer-Verlag Berlin and Heidelberg GmbH & Co. K. ISBN 3540575723. 
  7. ^ a b Douglas, R. W. (1972). A history of glassmaking. Henley-on-Thames: G T Foulis & Co Ltd. ISBN 0854291172. 
  8. ^ a b c B. H. W. S. de Jong, "Glass"; in "Ullmann's Encyclopedia of Industrial Chemistry"; 5th edition, vol. A12, VCH Publishers, Weinheim, Germany, 1989, ISBN 3-527-20112-5, p 365–432.
  9. ^ PFG Glass
  10. ^ a b Glass melting, Pacific Northwest National Laboratory
  11. ^ Glass melting in the laboratory
  12. ^ P. F. McMillan "Polyamorphic transformations in liquids and glasses" Journal of Materials Chemistry 14, 1506–1512 (2004)
  13. ^ carbon dioxide glass created in the lab 15 June 2006, Retrieved 3 August 2006
  14. ^ a b S. A. Baeurle et al. "On the glassy state of multiphase and pure polymer materials" Polymer 47, 6243–6253 (2006)
  15. ^ a b "Folmer, J. C. W.; Franzen, Stefan." Study of polymer glasses by modulated differential scanning calorimetry in the undergraduate physical chemistry laboratory" Journal of Chemical Education (2003), 80(7), 813
  16. ^ P.S. Salmon "Order within disorder" Nature Materials, 1(87), (2002)
  17. ^ M.I. Ojovan, W.E. Lee "Topologically disordered systems at the glass transition" J. Phys.: Condensed Matter, 18, 11507–11520 (2006)
  18. ^ a b c d Philip Gibbs. "Is glass liquid or solid?". Retrieved on 2007-03-21. 
  19. ^ "Philip Gibbs" Glass Worldwide, (may/june 2007), pp 14–18
  20. ^ Jim Loy. "Glass Is A Liquid?". Retrieved on 2007-03-21. 
  21. ^ Florin Neumann. "Glass: Liquid or Solid – Science vs. an Urban Legend". Retrieved on 2007-04-08. 
  22. ^ Chang, Kenneth (2008-07-29). "The Nature of Glass Remains Anything but Clear". New York Times. Retrieved on 2008-07-29. 
  23. ^ Dr Karl's Homework: Glass Flows
  24. ^ "Do Cathedral Glasses Flow?" Am. J. Phys., 66 (May 1998), pp 392–396
  25. ^ a b "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
  26. ^ Soda-lime glass for containers is slightly different from soda-lime glass for windows (also called flat glass or float glass). Float glass has a higher magnesium oxide content as compared to container glass, and a lower silica and calcium oxide content. For further details see main article Soda-lime glass.
  27. ^ A.J. Leadbettera and A.C. Wrigh "Diffraction studies of glass structure: II. The structure of vitreous germania" Journal of non-crystalline solids, 7:37–52 (1972)
  28. ^ M. Micoulaut et al. "Simulated structural and thermal properties of glassy and liquid germania" Physical Review E, 73:031504 (2006)
  29. ^ 35 Tg data for GeO2 from SciGlass 6.7
  30. ^ a b Kotkata et al. "Effect of thallium on the optical properties of amorphous GeSe2 and GeSe4 films" J. Phys. D: Appl. Phys. 27 pp 623–627 (1994)
  31. ^ P. S. Salmon et al. "Glass Fragility and Atomic Ordering on the Intermediate and Extended Range" Physical Review Letters, 96, 235502 (2006)
  32. ^ a b The subscript D indicates that the refractive index n was measured at a wavelength λ of 589.29 nm, F and C indicate 486.13 nm (blue) and 656.27 nm (red) respectively (see article Fraunhofer lines)
  33. ^ L. G. Hwa and W.C. Chao "Velocity of sound and elastic properties of lanthanum gallo-germanate glasses" Materials Chemistry and Physics, 94, 37–41 (2005)
  34. ^ Valid for glass composition, wt%: 80.7 SiO2, 13.1 B2O3, 4.1 Na2O, 2.1 Al2O3; Reference: Baak N. T. E. A. and Rapp C. F., GB Patent No. 1132885 Cl C 03 C 3/04, Abridg. Specif., 1968; Assignee: Owens-Illinois, Inc. (US).
  35. ^ International Organization for Standardization, Procedure 719 (1985)
  36. ^ Substances Used in the Making of Coloured Glass (David M Issitt). Retrieved 3 August 2006
  37. ^ "Glass Online: The History of Glass". Retrieved on 2007-10-29. 
  38. ^ True glazing over a ceramic body was not used until many centuries after the production of the first glass.
  39. ^ Agricola, Georgius, De re metallica, translated by Herbert Clark Hoover and Lou Henry Hoover, Dover Publishing. De Re Metallica Trans. by Hoover Online Version Page 586 Retrieved = 12 September 2007
  40. ^ a b c Gowlett 1997, page 276–277
  41. ^ a b c d e Ghosh 1990, page 219
  42. ^ "Ornaments, Gems etc." (Ch. 10) in Ghosh 1990
  43. ^ Ahmad Y Hassan, Assessment of Kitab al-Durra al-Maknuna, History of Science and Technology in Islam.
  44. ^ Ahmad Y Hassan, The Manufacture of Coloured Glass, History of Science and Technology in Islam.
  45. ^ Roshdi Rashed (1990), "A Pioneer in Anaclastics: Ibn Sahl on Burning Mirrors and Lenses", Isis 81 (3), p. 464–491 [464–468].
  46. ^ Ahmad Y Hassan, Transfer Of Islamic Technology To The West, Part III: Technology Transfer in the Chemical Industries, History of Science and Technology in Islam.
  47. ^ Donny L. Hamilton. "Glass Conservation". Conservation Research Laboratory, Texas A&M University. Retrieved on 2007-03-21. 
  48. ^ Georg Agricola De Natura Fossilium, Textbook of Mineralogy, M.C. Bandy, J. Bandy, Mineralogical Society of America, 1955, Page 111 Section on Murano Glass, De Natura Fossilium Retrieved 2007-09-12
  49. ^ "Corning Museum of Glass". Retrieved on 2007-10-14. 
  50. ^ "Waterford Crystal Vistors Centre". Retrieved on 2007-10-19. 
  51. ^ "Depression Glass". Retrieved on 2007-10-19. 
  52. ^ the Harvard Museum of Natural History's page on the exhibit


  • Brugmann, Birte. Glass Beads from Anglo-Saxon Graves: A Study on the Provenance and Chronology of Glass Beads from Anglo-Saxon Graves, Based on Visual Examination. Oxbow Books, 2004. ISBN 1-84217-104-6
  • Ghosh, Amalananda (1990). An Encyclopaedia of Indian Archaeology. BRILL. ISBN 9004092625. 
  • Gowlett, J.A.J. (1997). High Definition Archaeology: Threads Through the Past. Routledge. ISBN 0415184290. 
  • Noel C. Stokes; The Glass and Glazing Handbook; Standards Australia; SAA HB125–1998

External links


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary



Wikipedia has an article on:
Most common English words: native « members « fortune « #959: glass » silver » winter » expect


From Old English glæs, cognate with Old Saxon and Old High German glas (amber), which (in OHG) is attested as a gloss for Latin electrum (amber). These words are developed from Proto-Germanic *glaso-. Possibly ultimately from the Proto-Germanic root *glō-, *to shine (compare glow).



a glass (2) of milk
countable and uncountable; plural glasses
glass (countable and uncountable; plural glasses)
  1. (uncountable) A solid, transparent substance made by melting sand with a mixture of soda, potash and lime.^ A more important outcome, however, of Italian influence was the production, in emulation of Venetian glass, of a glass made of refined potash, lime and sand, which was more colourless than the material it was intended to imitate.

    ^ The invention, if it may be regarded as one, consisted in eliminating lime from the glass mixture, substituting refined potash for soda, and using a very large proportion of lead oxide.

    ^ The essential materials of which these mixtures are made are, for English flint glass, sand , carbonate of potash and red lead ; for plate and sheet glass, sand, carbonate or sulphate of soda.

    The tabletop is made of glass.
  2. A vessel from which one drinks, especially one made of glass, plastic, or similar translucent or semi-translucent material.^ Although most of the vessels of this mille fiori glass were small, some were made as large as 20 in.

    ^ The coloured glass is usually not of one bright colour throughout, but semi-transparent and marbled; the colours in many instances are singularly fine and harmonious.

    ^ It is probable that the glass drinking-vessels, which have been found in pre-Christian Anglo-Saxon tombs, were introduced from Germany.

    Fill my glass with milk please.
  3. The quantity of liquid contained in such a vessel.
    Would you like a glass of milk?
  4. (physics, uncountable) Amorphous (non-crystalline) substance.
    A popular myth is that window glass actually is an extremely viscous liquid.
  5. (uncountable) Glassware.
    We collected art glass.
  6. A mirror.
    She adjusted her lipstick in the glass.
  7. A magnifying glass or telescope.
  8. (basketball, colloquial) The backboard.
    He caught the rebound off of the glass.
  9. (ice hockey) The clear, protective screen surrounding a hockey rink.
    He fired the outlet pass off the glass.

Derived terms



glass (no comparative or superlative)
  1. (colloquial) Fragile.
    He has a glass ankle.



to glass
Third person singular
Simple past
Past participle
Present participle
to glass (third-person singular simple present glasses, present participle glassing, simple past and past participle glassed)
  1. (transitive) To furnish with glass; to glaze.
  2. (transitive) To enclose with glass.
  3. (transitive, British, colloquial) To strike (someone), particularly in the face, with a drinking glass with the intent of causing injury.
    • 1987, John Godber, Bouncers [1]
      JUDD. Any trouble last night? / LES. Usual. Couple of punks got glassed.
    • 2002, Geoff Doherty, A Promoters Tale [2]
      I often mused on what the politicians or authorities would say if they could see for themselves the horrendous consequences of someone who’d been glassed, or viciously assaulted.
    • 2003, Mark Sturdy, Pulp [3]
      One night he was in this nightclub in Sheffield and he got glassed by this bloke who’d been just let out of prison that day.
  4. To bombard an area with such intensity (nuclear bomb, fusion bomb, etc) as to melt the landscape into glass.


  1. (basketball) A warning called out to alert teammates that a shot is about to rebound off the backboard.
    The point guard launched a wobbly attempt at a three-pointer and immediately called "Glass!"


  • Anagrams of aglss
  • slags


Etymology 1

From Old Irish glas (blue-grey, green)


  1. green (of nature)
  2. grey (of animal)
  3. ashen (color/colour)
  4. verdant
  5. soft
  6. pale
  7. pasty
  8. raw
  9. unfledged
  10. sappy
  11. callow (of youth)

Etymology 2

From Old Irish glas (lock, clasp)


glass m. (plural glish)
  1. lock




Inflection for glass Singular Plural
common Indefinite Definite Indefinite Definite
Base form glass glassen glassar glassarna
Possessive form glass glassens glassars glassarnas
glass c.
  1. ice cream

Simple English

Simple English Wiktionary has the word meaning for:

Glass is a hard material that can be made in many shapes. It is usually transparent, but it can also be made in colours.

Glass is often used to make windows and bottles. Many churches have windows made of colored glass.

The word "glass" can also refer to a drink container. It does not have to be made of glass, but can be made of any material, for example plastic.

Glass is used to make lenses. The word "glasses" is often used to mean eyeglasses.

The myth that glass is actually a liquid comes from the fact that old windows in houses and churches (2-300 years old) are sometimes a little out of shape: thicker at the bottom than the top. This phenomenon is actually due to the process of glass manufacture in the past which led to the glass pane being thicker at one edge than the other. It was sensible to install the windows with the thick edge at the bottom. Sometimes a window can be found with the thick edge at the top of the window.

Other websites

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Citable sentences

Up to date as of December 16, 2010

Here are sentences from other pages on Glass, which are similar to those in the above article.

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