Glass

This property can be seen in the University of Queensland's pitch drop experiment, where each drop has taken approximately 10 years to fall into the beaker. . Note that pitch, another seemingly-solid material, is in fact a highly viscous liquid, 100 billion times as viscous as water. HD may refer to:. Occasionally such glass has been found thinner side down, as would be caused by carelessness at the time of installation. Mustard gas. When actually installed in a window frame, the glass would be placed thicker side down for the sake of stability and visual sparkle. Hilda Doolittle, also known as H.D., American poet.

The pieces were not, however, absolutely flat; the edges of the disk would be thicker because of centripetal forces. Higher Diploma, an academic award. This plate was then cut to fit a window. Hybrid drive, a type of notebook hard drive that utilizes a large buffer. The likely source of this belief is that when panes of glass were commonly made by glassblowers, the technique that was used was to spin molten glass so as to create a round, mostly flat and even plate (the Crown glass process, described above). High Density, in reference to a floppy disk or other magnetic media. It is then assumed that the glass was once uniform, but has flowed to its new shape. High definition television, HD DVD, high definition media formats.

Supporting evidence that is often offered is that old windows are often thicker at the bottom than at the top. Henry Draper Catalogue, a sequential numbering system for stars ordered by right ascension. One common misconception is that glass is a super-cooled liquid of practically infinite viscosity when at room temperature. Hard disk, or hard drive, a type of computer storage hardware (also HDD for hard disk drive). See also Window. HD, a human gene that makes a protein called huntingtin which plays an important role in Huntington's disease. These glass types can be further utilised by the following processes:. Huntington's disease.

Several methods of producing glass for applications have been developed, including:. Hormone disruptor. Foamed glass, made from waste glass, can be used as lightweight, closed-cell insulation. Hodgkin's disease. Glass fibre insulation is common in roofs and walls. Attention-deficit hyperactivity disorder, known as Hyperactivity Disorder (HD), as in AD/HD. Glass in buildings can be of a safety type, including wired, toughened and laminated glasses. Home Depot, a chain of home improvement warehouse retailers.

Typical uses for glass in buildings include as a transparent material for windows in the building envelope, as internal glazed partitions and as architectural features. Harley-Davidson, an iconic American motorcycle manufacturer. Glass has been used in buildings since the 11th century. Hit Dice how many dice of hit points your character has, an indication of his or her health and durability. Main articles: Architectural Glass and Glazing. Stained glass is an art form with a long history; many churches have beautiful stained-glass windows.

See the Harvard Museum of Natural History's page on the exhibit for further information. The Blaschka Glass Flowers are still an inspiration to glassblowers today. These were lampworked by Leopold Blaschka and his son Rudolph, who never revealed the method he used to make them. The Harvard Museum of Natural History has a collection of extremely detailed models of flowers made of painted glass.

A significant exception is the collection of pieces by the Blaschkas. Colored glass is often used, and sometimes the glass is painted, although many glassblowers consider this crude. Objects made out of glass include vessels (bowls, vases, and other containers), paperweights, marbles, beads, smoking pipes, bongs, and sculptures. Glass can also be cut with a diamond saw, and polished to give gleaming facets.

Glass that is manipulated in a kiln is called warm glass, and traditional stained glass work is commonly called cold glass work. Someone who works with hot glass is called a glassblower or lampworker, and these techniques are how most fine glassware is created. There are many techniques for creating fine glass art; each is suitable for certain kinds of object and unsuitable for others. The term "crystal glass", derived from rock crystal, has come to denote high-grade colourless glass, often containing lead, and is sometimes applied to any fine hand-blown glass.

Some artists in glass include Lino Tagliapietra, Sidney Waugh, Rene Lalique, Dale Chihuly, and Louis Comfort Tiffany, who were responsible for extraordinary glass objects. Even with the availability of common glassware, hand blown or lampworked glassware remains popular for its artistry. Volcanic glasses, such as obsidian, have long been used to make stone tools, and flint knapping techniques can easily be adapted to mass-produced glass. Most such glass is mass-produced using various industrial processes, but most large laboratories need so much custom glassware that they keep a glassblower on staff.

For the most demanding applications, quartz glass is used, although it is very difficult to work. For these applications, borosilicate glass (such as Pyrex) is usually used for its strength and low coefficient of thermal expansion, which gives greater resistance to thermal shock and allows for greater accuracy in laboratory measurements when heating and cooling experiments. In laboratories doing research in chemistry, biology, physics and many other fields, flasks, test tubes, lenses and other laboratory equipment are often made of glass. Drinking glasses, bowls, and bottles are often made of glass, as are light bulbs, mirrors, the picture tubes of computer monitors and televisions, and windows.

Many household objects are made of glass. Since glass is strong and unreactive, it is a very useful material. See also: Broad sheet, Blown plate, Polished plate, Cylinder blown sheet, Machine drawn cylinder sheet. This reduced manufacturing costs and, combined with a wider use of coloured glass, led to cheap popular glassware in the 1930s, which later became known as Depression glass.

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 mold with the image already on the surface of the glass. Traditionally this was done by a trained artisan after the glass was blown or cast. Art is sometimes etched into glass via acid or other caustic substance (causing the image to be eaten into the glass). Blenko in the 1920s.

The cylinder method of creating flat glass was first used in the United States of America by William J. The invention of the glass pressing machine in 1827 allowed the mass production of inexpensive glass articles. Around 1688, a process for casting glass was developed, which led to its becoming a much more commonly used material. Venetian glass was highly prized between the 10th and 14th centuries as they managed to keep the process secret.

The disk would then be cut into panes. In this process, the glassblower would spin around 9 lb (4 kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 ft (1.5 m) in diameter. The Crown glass process was used up to the mid-1800s. Eventually some of the Venetian glass workers moved to other areas of northern Europe and glass making spread with them.

The centre for glass making from the 14th century was Venice, which developed many new techniques and became the centre of a lucrative export trade in dinner ware, mirrors, and other luxury items. Until the 12th century, stained glass (i.e., glass with some colouring impurities, usually metals) was not widely used. This technique was perfected in 13th century Venice. The 11th century saw the emergence, in Germany, of new ways of making sheet glass by blowing spheres, swinging these out to form cylinders, cutting these while still hot, and then flattening the sheets.

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

When gem-cutters learned to cut glass, they found clear glass was an excellent refractor of light, the popularity of cut clear glass soared, that of coloured glass diminished. Glassmakers learned to make coloured glass by adding metallic compounds and mineral oxides to produce brilliant hues of red, green, and blue - the colours of gemstones. Common glass today usually has a slight green or blue tint, arising from these same impurities. This colour is caused by the varying amounts of naturally occurring iron impurities in the sand.

The colour of "natural glass" is green to bluish green. This was the discovery of glassblowing, both free-blowing and mould-blowing. In the first century BC, somewhere at the eastern end of the Mediterranean, a new invention caused a true revolution in the glass industry. As time passed, it was discovered (most likely by a potter) that if glass is heated until it becomes semi-liquid, it can be shaped and left to cool in a new, solid, independently standing shape.

Small pieces of coloured glass were considered valuable and often rivalled precious gems as jewellery items. The earliest use of glass was as a coloured, opaque, or transparent glaze applied to ceramics before they were fired. Glass was made from sand, plant ash and lime. During the Roman Empire many forms of glass were created, usually for vases and bottles.

In the first century BC the technique of blowing glass was developed and what had once been an extremely rare and valuable item became much more common. Glass making instructions were first documented in Egypt around 1500 BC, when glass was used as a glaze for pottery and other items. Naturally occurring glass, such as obsidian, has been used since the stone age. New coloured glasses are frequently discovered.

The chemistry involved is complex and not well understood. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. Silver compounds (notably silver nitrate) can produce a range of colors from orange-red to yellow. Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic.

Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or green colour. Metallic gold, in very small concentrations (around 0.001%), produces a rich ruby-coloured glass, while lower concentrations produces a less intense red, often marketed as "cranberry". Adding titanium produces yellowish-brown glass. Nickel, depending on the concentration, produces blue, or violet, or even black glass.

Pure metallic copper produces a very dark red, opaque glass, which is sometimes used as a substitute for gold in the production of ruby-coloured glass. 2 to 3% of copper oxide produces a turquoise colour. Tin oxide with antimony and arsenic oxides produce an opaque white glass, first used in Venice to produce an imitation porcelain. Small concentrations of cobalt (0.025 to 0.1%) yield blue glass.

Like manganese, selenium can be used in small concentrations to decolorize glass, or in higher concentrations to impart a reddish colour. Manganese can be added in small amounts to remove the green tint lent by iron, or in higher concentrations to give glass an amethyst colour. Metals and metal oxides are added to glass during its manufacture to change its colour. sol gel is a good example of glass prepared in this way.

By polymerizing glass it is possible to embed active molecules, such as enzymes, to add a new level of functionality to the glass vessels. Putting in additives that modify the properties of glass is problematic, because the high temperature of preparation destroys most of them. An innovative way for making glass involves preparation by polymerization. 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).

Thorium oxide gives glass a high refractive index and low dispersion, and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern glasses. Adding barium also increases the refractive index. 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. As well as soda and lime, most common glass has other ingredients added to change its properties.

Soda-lime glasses account for about 90% of manufactured glass. The resulting glass contains about 70% silica and is called a soda-lime glass. However, the soda makes the glass water-soluble, which is obviously undesirable, so lime (calcium oxide, CaO) is the third component, added to restore insolubility. One is soda (sodium carbonate Na₂CO₃), or potash, the equivalent potassium compound, which lowers the melting point to about 1000 °C (1800 °F).

Pure silica (SiO₂) has a melting point of about 2000 °C (3600 °F), and while it can be made into glass for special applications (see fused quartz), two other substances are always added to common glass to simplify processing. Collecting obsidian from national parks and some places may be prohibited by law, but the same toolmaking techniques can be applied to industrially-made glass. Obsidian is a raw material for flint knappers, who have used it to make extremely sharp knives since the stone age. This glass is called obsidian, and is usually black with impurities.

Glass is sometimes created naturally from volcanic magma. The glasses are arranged by composition, refractive index, and Abbe number. For example, BK7 is a low-dispersion borosilicate crown glass, and SF10 is a high-dispersion dense flint glass. Glasses used for making optical devices are commonly categorized using a six-digit glass code, or alternatively a letter-number code from the Schott Glass catalogue.

Amorphous SiO₂ is also used as a dielectric material in integrated circuits, due to the smooth and electrically neutral interface it forms with silicon. Undersea cables have sections doped with erbium, which amplify transmitted signals by laser emission from within the glass itself. Individual fibres are given an equally transparent core of SiO₂/GeO₂ glass, which has only slightly different optical properties (the germanium contributing to a higher index of refraction). This type of glass can be made so pure that hundreds of kilometres of glass are transparent at infrared wavelengths in fibre optic cables.

Pure SiO₂ glass (also called fused quartz) does not absorb UV light and is used for applications that require transparency in this region, although it is more expensive. This is due to the addition of compounds such as soda ash (sodium carbonate). Ordinary glass does not allow light at a wavelength of lower than 400 nm, also known as ultraviolet light or UV, to pass. The transparency is due to an absence of electronic transition states in the range of visible light, and to the fact that such glass is homogeneous on all length scales greater than about a wavelength of visible light (inhomogeneities cause light to be scattered, breaking up any coherent image transmission).

One of the most obvious characteristics of ordinary glass is that it is transparent to visible light (not all glassy materials are). Common glass contains about 70% amorphous silicon dioxide (SiO₂), which is the same chemical compound found in quartz, and its polycrystalline form, sand. These properties can be modified, or even changed entirely, with the addition of other compounds or heat treatment. Glass is, however, brittle and will break into sharp shards.

These desirable properties lead to a great many uses of glass. In its pure form, glass is a transparent, relatively strong, hard-wearing, essentially inert, and biologically inactive material which can be formed with very smooth and impervious surfaces. The remainder of this article will be concerned with a specific type of glass—the silica-based glasses in common use as a building, container or decorative material. The term enamel is used to describe glass fused as a decorative or functional coating on metal.

Germanic tribes used the word glaes to describe amber, recorded by Roman historians as glaesum. Anglo-Saxons used the word glaer for amber. glaes. glas, A.S. The word glass comes from Latin glacies (ice) and corresponds to German Glas, M.E.

The resulting solid is amorphous, not crystalline like the sugar was originally, which can be seen in its conchoidal fracture. A simple example is when table sugar is melted and cooled rapidly by dumping the liquid sugar onto a cold surface. The materials definition of a glass is a uniform amorphous solid material, usually produced when a suitably viscous molten material cools very rapidly to below its glass transition temperature, thereby not giving enough time for a regular crystal lattice to form. .

This (along with chromatic aberration and other effects) limits the size of refracting telescopes, with the largest refractor in the World being the Yerkes Observatory telescope with a diameter of 102cm. The result is a loss of focus and is sometimes argued to occur not because of the liquid properties of glass but rather sagging of the telescope itself, but this is not correct. This sag happens because the lens is only supported around its edge. Glass in Refracting Telescopes, with objective lenses greater than 105cm in diameter, is observed to sag under its own under weight over time.

Similarly, it should not be possible to see Newton's rings between decade-old fragments of window glass—but this can in fact be quite easily done. If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then changes in optical telescope mirrors should be observable (by interferometry) in a matter of days—but this also is not observed. If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more—but this is not observed. In layperson's terms, he wrote that glass at room temperature is very strongly on the solid side of the spectrum from solids to liquids.

Phys, 66(5):392-5, May 1998). J. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer" (Am. Zanotto states "...the predicted relaxation time for GeO₂ at room temperature is 10³² years.

Writing in the American Journal of Physics, physicist Edgar D. double-glazing. application of a self-cleaning catylist. chemical strengthening.

toughening. laminating. figure rolled glass. float (annealed) glass.

polished plate glass. rolled plate glass. sheet glass. cylinder glass.