Glass

Moldavite, a natural glass formed by meteorite impact, from Besednice, Bohemia
A modern greenhouse in Wisley Garden, England, made from float glass
Clear glass light bulb

Glass is an amorphous (non-crystalline) solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.[1]

Strictly speaking, a glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising.[2][3][4][5][6] Many glasses contain silica as their main component and glass former.[7] The term "glass" is, however, 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.[7] Commonly, glass science and physics deal only with 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.

Contents

History

The history of creating glass can be traced back to 3500 BCE in Mesopotamia.

Glass production

Glass ingredients

Quartz sand (silica) as main raw material for commercial glass production
Oldest mouth-blown window-glass in Sweden (Kosta Glasbruk, Småland, 1742). In the middle is the mark from the glassblower'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 aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass.[8] Soda-lime glasses account for about 90% of manufactured glass.

Most common glass has other ingredients added to change its properties. Lead glass 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.

Another common glass ingredient is "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.

Composition and properties

There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb4+ replacing Si4+), or as a modifier.

The presence of non-bridging oxygens lowers the relative number of strong bonds in the material and disrupts the network, decreasing the viscosity of the melt and lowering the melting temperature.

The alkaline metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility however decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance.[9] Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.

Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and therefore is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.[10]

Addition of fluorine lowers the dielectric constant of glass. Fluorine is highly electronegative and attracts the electrons in the lattice, lowering the polarizability of the material. Such silicon dioxide-fluoride is used in manufacture of integrated circuits as an insulator. High levels of fluorine doping lead to formation of volatile SiF2O and such glass is then thermally unstable. Stable layers were achieved with dielectric constant down to about 3.5–3.7.[11]

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.[12] 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

A vitrification experiment for the study of nuclear waste disposal at Pacific Northwest National Laboratory.
Failed laboratory glass melting test. The striations must be avoided through good homogenization.

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali oxides and hydroxides, alkaline earth oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).[13] 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.[13][14]

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

Main article: Sol-gel

Silica-free glasses

Besides common silica-based glasses, many other inorganic and organic materials may also form glasses, including plastics (e.g., acrylic glass), amorphous 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.[7]

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, borate 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.[15] 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.[16]

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 mechanisms giving rise to the general properties of glasses? Question mark2.svg
The amorphous structure of glassy Silica (SiO2) in two dimensions. No long range order is present, however there is local ordering with respect to the tetrahedral arrangement of Oxygen (O) atoms around the Silicon (Si) atoms.

The standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching.[3][4][5][17] 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.[18] 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.[19] It is deemed that the bonding structure of glasses, although disordered, has the same symmetry signature (Hausdorff-Besicovitch dimensionality) as for crystalline materials.[20]

Glass versus a supercooled liquid

Glass is generally classed as an amorphous solid rather than a liquid.[17][21] 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.[22]

Some people consider glass to be a liquid due to its lack of a first-order phase transition[21][23] where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous 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 continuous.[20] 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.[5]

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.[24] 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 is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.

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.[25] In actuality, the 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.[26] 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.[27]

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, typically with the location of the pour centred in one of the panes (known as "bull's-eyes") for decorative effect. 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:

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.[18] 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 polystyrene and polypropylene are in a glassy state but they are not too far below their glass transition temperature as opposed to rubber which is used above its glass transition temperature. Their mechanical properties may well change over time and this is serious concern when applying these materials in construction. In general for polymers there is a relation between the glass transition temperature and the speed of the deformation.

Physical properties

Optical properties

Glass is in widespread use largely to the production of glass compositions that are transparent to visible wavelengths of light.

In contrast, polycrystalline materials in general do not transmit visible light. The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light. Light entering a polycrystal is repeatedly scattered until it re-emerges form the surface in random directions. This subsurface scattering mechanism,[29][30] together with scattering by surface irregularities, gives rise to diffuse reflection and hence although it does not absorb light the polycrystal is not transparent. This mechanism, which causes objects to be opaque, is a crucial mechanism for vision, because most objects are seen by our eyes through their diffuse reflection.[31]

Glass does not contain the internal subdivisions associated with grain boundaries in polycrystals and hence does not scatter light in the same manner as a polycrystalline material. The surface of a glass is often smooth since during glass formation the molecules of the supercooled liquid are not forced to dispose in rigid crystal geometries and can follow surface tension, which imposes a microscopically smooth surface. These properties, which give glass its clearness, can be retained even if glass is partially absorbing (colored, see below).

Glass has the ability to refract, reflect and transmit light following geometrical optics, without scattering it, and it is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. According to Fresnel equations, the reflectivity of a sheet of glass is about 4% per each surface (at normal incidence), and its transmissivity about 92%.

Color

See also: Transparent_materials#Absorption of light in solids
Common soda-lime float glass appears green in thick sections because of Fe2+ impurities.

Many glasses have a chemical composition which includes what are referred to as absorption centers. This may cause them to be selective in their absorption of visible lightwaves (or white light frequencies). They absorb certain portions of the visible spectrum, while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected back or transmitted for our physical observation. This is what gives rise to color.

Thus, 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).[7] 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%[32] 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.[33] Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide.

Optical waveguides

The propagation of light through a multi-mode optical fiber.
A laser bouncing down an acrylic 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 materials science 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.

Modern glass art

A vase being created at the Reijmyre glassworks, Sweden
Paperweight with items inside the glass, Corning Museum of Glass
A glass sculpture by Dale Chihuly, “The Sun” at the “Gardens of Glass” exhibition in Kew Gardens, London. The piece is 13 feet (4 metres) high and made from 1000 separate glass objects.
Glass tiles mosaic (detail).

From the 19th century, various types of fancy glass started to become significant branches of the decorative arts. Cameo glass was revived for the first time since the Romans, initially mostly used for pieces in a neo-classical style. The Art Nouveau movement in particular made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy important names in the first French wave of the movement, producing colored vases and similar pieces, often in cameo glass, and also using lustre techniques. Louis Comfort Tiffany in America specialized in secular stained glass, mostly of plant subjects, both in panels and his famous lamps. From the 20th century, some glass artists began to class themselves as in effect sculptors working in glass, and as part of the fine arts.

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.[34] 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.[35] 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.

Museums

Apart from historical collections in general museums, modern 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.[36]

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.[37]

See also

References

  1. ↑ Douglas, R. W. (1972). A history of glassmaking. Henley-on-Thames: G T Foulis & Co Ltd. ISBN 0854291172. 
  2. ↑ ASTM definition of glass from 1945; also: DIN 1259, Glas – Begriffe für Glasarten und Glasgruppen, September 1986
  3. ↑ 3.0 3.1 Zallen, R. (1983). The Physics of Amorphous Solids. New York: John Wiley. ISBN 0471019682. 
  4. ↑ 4.0 4.1 Cusack, N. E. (1987). The physics of structurally disordered matter: an introduction. Adam Hilger in association with the University of Sussex press. ISBN 0852748299. 
  5. ↑ 5.0 5.1 5.2 Elliot, S. R. (1984). Physics of Amorphous Materials. Longman group ltd. 
  6. ↑ Horst Scholze (1991). Glass – Nature, Structure, and Properties. Springer. ISBN 0-387-97396-6. 
  7. ↑ 7.0 7.1 7.2 7.3 Werner Vogel (1994). Glass Chemistry (2 ed.). Springer-Verlag Berlin and Heidelberg GmbH & Co. K. ISBN 3540575723. 
  8. ↑ 8.0 8.1 8.2 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, pp. 365–432.
  9. ↑ Eric Le Bourhis (2007). Glass: Mechanics and Technology. Wiley-VCH. p. 74. ISBN 3527315497. http://books.google.com/?id=34W4ZNDBHqQC&pg=PA64&dq=%22borate+glass%22&cd=1#v=onepage&q=%22borate%20glass%22. 
  10. ↑ James F. Shackelford, Robert H. Doremus (2008). Ceramic and Glass Materials: Structure, Properties and Processing. Springer. p. 158. ISBN 0387733612. http://books.google.com/?id=ASIYuNCp81YC&pg=PA158&dq=%22glass+solders%22&cd=3#v=onepage&q=%22glass%20solders%22. 
  11. ↑ Robert Doering, Yoshio Nishi (2007). Handbook of semiconductor manufacturing technology. CRC Press. pp. 12–3. ISBN 1574446754. http://books.google.com/?id=PsVVKz_hjBgC&pg=SA12-PA3&dq=semiconductor+failure+microphotograph&cd=5#v=onepage&q=. 
  12. ↑ "PFG Glass". Pfg.co.za. http://www.pfg.co.za/about%20glass.htm. Retrieved 2009-10-24. 
  13. ↑ 13.0 13.1 "Glass melting, Pacific Northwest National Laboratory". Depts.washington.edu. http://depts.washington.edu/mti/1999/labs/glass_ceramics/mst_glass.html. Retrieved 2009-10-24. 
  14. ↑ Alexander Fluegel. "Glass melting in the laboratory". Glassproperties.com. http://glassproperties.com/melting/. Retrieved 2009-10-24. 
  15. ↑ P. F. McMillan (2004). "Polyamorphic transformations in liquids and glasses". Journal of Materials Chemistry 14: 1506–1512. doi:10.1039/b401308p. 
  16. ↑ carbon dioxide glass created in the lab 15 June 2006, www.newscientisttech.com. Retrieved 3 August 2006.
  17. ↑ 17.0 17.1 S. A. Baeurle et al. (2006). "On the glassy state of multiphase and pure polymer materials". Polymer 47: 6243–6253&year=2006. doi:10.1016/j.polymer.2006.05.076. 
  18. ↑ 18.0 18.1 Folmer, J. C. W.; Franzen, Stefan (2003). "Study of polymer glasses by modulated differential scanning calorimetry in the undergraduate physical chemistry laboratory". Journal of Chemical Education 80 (7): 813. doi:10.1021/ed080p813. http://jchemed.chem.wisc.edu/Journal/Issues/2003/Jul/abs813.html. 
  19. ↑ P.S. Salmon (2002). "Order within disorder". Nature Materials 1 (2): 87. doi:10.1038/nmat737. PMID 12618817. 
  20. ↑ 20.0 20.1 M.I. Ojovan, W.E. Lee (2006). "Topologically disordered systems at the glass transition". J. Phys.: Condensed Matter 18: 11507–11520. doi:10.1088/0953-8984/18/50/007. 
  21. ↑ 21.0 21.1 21.2 21.3 Philip Gibbs. "Is glass liquid or solid?". http://math.ucr.edu/home/baez/physics/General/Glass/glass.html. Retrieved 2007-03-21. 
  22. ↑ "Philip Gibbs" Glass Worldwide, (May/June 2007), pp. 14–18
  23. ↑ Jim Loy. "Glass Is A Liquid?". http://www.jimloy.com/physics/glass.htm. Retrieved 2007-03-21. 
  24. ↑ Florin Neumann. "Glass: Liquid or Solid – Science vs. an Urban Legend". http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html. Retrieved 2007-04-08. 
  25. ↑ Chang, Kenneth (2008-07-29). "The Nature of Glass Remains Anything but Clear". New York Times. http://www.nytimes.com/2008/07/29/science/29glass.html?ex=1375070400&en=048ade4011756b24&ei=5124&partner=permalink&exprod=permalink. Retrieved 2008-07-29. 
  26. ↑ "Dr Karl's Homework: Glass Flows". Abc.net.au. 2000-01-26. http://www.abc.net.au/science/k2/homework/s95602.htm. Retrieved 2009-10-24. 
  27. ↑ H. Halem. "Does Glass Flow". http://www.glassnotes.com/WindowPanes.html. Retrieved 2010-09-02. 
  28. ↑ Zanotto, Edgar Dutra (1998). "Do Cathedral Glasses Flow?". American Journal of Physics 66: 392–396. doi:10.1119/1.19026. 
  29. ↑ P.Hanrahan and W.Krueger (1993), Reflection from layered surfaces due to subsurface scattering. In SIGGRAPH ’93 Proceedings, J. T. Kajiya, Ed., vol. 27, pp. 165–174.
  30. ↑ H.W.Jensen et al. (2001), A practical model for subsurface light transport. In 'Proceedings of ACM SIGGRAPH 2001', pp. 511–518
  31. ↑ Kerker, M. (1909). The Scattering of Light. New York: Academic. 
  32. ↑ "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
  33. ↑ Substances Used in the Making of Coloured Glass 1st.glassman.com (David M Issitt). Retrieved 3 August 2006.
  34. ↑ "Waterford Crystal Visitors Centre". http://www.waterfordvisitorcentre.com/. Retrieved 2007-10-19. 
  35. ↑ "Depression Glass". http://www.glassonweb.com/articles/article/201/. Retrieved 2007-10-19. 
  36. ↑ "Corning Museum of Glass". http://www.cmog.org/index.asp?pageId=1276. Retrieved 2007-10-14. 
  37. ↑ the Harvard Museum of Natural History's page on the exhibit

Bibliography

External links

Glass science topics
Basics

Glass definition · Is glass a liquid or a solid? · Glass transition · Physics of glass · Supercooling
Glass formulation

AgInSbTe · Bioglass · Borophosphosilicate glass · Borosilicate glass · Ceramic glaze · Chalcogenide glass · Cobalt glass · Cranberry glass · Crown glass · Flint glass · Fluorosilicate glass · Fused quartz · GeSbTe · Gold ruby glass · Lead glass · Milk glass · Phosphosilicate glass · Photochromic lens glass · Silicate glass · Soda-lime glass · Sodium hexametaphosphate · Soluble glass · Tellurite glass · Ultra low expansion glass · Uranium glass · Vitreous enamel · Wood's glass · ZBLAN
Glass-ceramics

Bioactive glass · CorningWare · Glass-ceramic-to-metal seals · Macor · Zerodur
Glass preparation

Annealing · Chemical vapor deposition · Glass batch calculation · Glass forming · Glass melting · Glass modeling · Ion implantation · Liquidus temperature · Sol-gel technique · Viscosity
Optics

Achromat · Dispersion · Gradient index optics · Hydrogen darkening · Optical amplifier · Optical fiber · Optical lens design · Photochromic lens · Photosensitive glass · Refraction · Transparent materials
Surface modification

Anti-reflective coating · Chemically strengthened glass · Corrosion · Dealkalization · DNA microarray · Hydrogen darkening · Insulated glazing · Porous glass · Self-cleaning glass · Sol-gel technique · Toughened glass
Diverse topics

Diffusion · Glass-coated wire · Glass databases · Glass electrode · Glass fiber reinforced concrete · Glass history · Glass ionomer cement · Glass microspheres · Glass-reinforced plastic · Glass science institutes · Glass-to-metal seal · Porous glass · Prince Rupert's Drops · Radioactive waste vitrification · Windshield
Glass forming techniques
Commercial techniques
Float glass process · Blowing and pressing (containers) · Extrusion / Drawing (fibers, glasswool) · Drawing (optical fibers) · Precision glass moulding · Overflow downdraw method · Pressing · Casting · Cutting · Flame polishing · Chemical polishing · Diamond turning · Rolling
Artistic and historic techniques
Beadmaking · Blowing · Blown plate · Broad sheet · Caneworking · Crown glass · Cylinder blown sheet · Engraving  · Etching · Fourcault process · Fusing · Lampworking · Machine drawn cylinder sheet · Millefiori · Polished plate · Slumping · Stained glass fusing · Stained glass production
See also
Glossary of glass art terms
Glass makers and brands
Contemporary
companies

Anchor Hocking · Arc International · Ardagh · Armashield · Asahi · Aurora Glass Foundry · Baccarat · Blenko Glass Company · Bodum · Corning · Dartington Crystal · Daum · Edinburgh Crystal · Fanavid · Fenton Art Glass Company · Firozabad glass industry · Franz Mayer · Glava · Glaverbel · Hardman & Co. · Heaton, Butler and Bayne · Holmegaard Glassworks · Holophane · Hoya · Kingdom of Crystal · Kokomo Opalescent Glass Works · Kosta Glasbruk · Libbey Owens Ford · Liuli Gongfang · Iittala · Luoyang · Johns Manville · Mats Jonasson Målerås · Moser Glass · Mosser Glass · Nippon Sheet Glass · Ohara · Orrefors Glasbruk · Osram · Owens Corning · Owens-Illinois · Pauly & C. - Compagnia Venezia Murano · Phu Phong · Pilkington · PPG · Preciosa · Quinn Group · Riedel · Royal Leerdam Crystal · Saint-Gobain · Samsung Corning Precision Glass · Schonbek · Schott · Shrigley and Hunt · Steuben Glass · Sterlite Optical Technologies · Swarovski · Tyrone Crystal · Val Saint Lambert · Verrerie of Brehat · Waterford ·

Watts & Co · World Kitchen · Xinyi Glass · Zwiesel
Historic
companies

Bakewell Glass · Belmont Glass Company · Boston and Sandwich Glass Company · Brockway Glass · Carr Lowrey Glass Company · Cambridge Glass · Chance Brothers · Clayton and Bell · Duncan & Miller · Dunbar Glass · Fostoria Glass Company · General Glass Industries · Alexander Gibbs · Grönvik glasbruk · Hazel-Atlas · Heisey · Hemingray Glass Company · Knox Glass Bottle Company · Lavers, Barraud and Westlake · Manufacture royale de glaces de miroirs · Morris & Co. · Old Dominion Glass Company · James Powell and Sons · Ravenhead glass · The Root Glass Company · Sneath Glass Company · Ward and Hughes · Westmoreland Glass Company · Wheaton Industries  · Whitall Tatum Company · White Glass Company · Worshipful Company
Glassmakers

John Adams · Richard M. Atwater · Frederick Carder · Irving Wightman Colburn · Henry Crimmel · Henry Clay Fry · Friedrich · A. H. Heisey · Libbey · Antonio Neri · Alastair Pilkington · Salviati · Otto Schott · S. Donald Stookey · W. E. S. Turner · John M. Whitall
Trademarks
and brands

Bohemian glass · Bomex · Burmese glass · Chevron bead · Corelle · CorningWare · Cranberry glass · Cristallo · Duran · Endural · Favrile · Fire King · Gold Ruby · MACOR · Murano glass · Opaline glass · Pyrex · Ravenhead glass · Tiffany glass · Vitrite · Vitrolite · Vycor · Waterford Crystal · Wood's glass · Zerodur