Float glass is a sheet of glass made by floating molten glass on a bed of molten metal tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and flat surfaces. Modern windows are made from float glass. Most float glass is soda-lime glass, but minor quantities of specialty borosilicate and flat panel display glass are produced using the float glass process; the float glass process is known as the Pilkington process, named after the British glass manufacturer Pilkington, which pioneered the technique in the 1950s at their production site in St Helens, Merseyside. Until the 16th century, window glass or flat glass was cut from large discs of crown glass. Larger sheets of glass were made by blowing large cylinders which were cut open and flattened cut into panes. Most window glass in the early 19th century was made using the cylinder method. The'cylinders' were 6 to 8 feet long and 10 to 14 inches in diameter, limiting the width that panes of glass could be cut, resulting in windows divided by transoms into rectangular panels.
The first advances in automating glass manufacturing were patented in 1848 by Henry Bessemer, an English engineer. His system produced a continuous ribbon of flat glass by forming the ribbon between rollers; this was an expensive process. If the glass could be set on a smooth, flat body, like the surface of an open pan of calm liquid, this would reduce costs considerably. Attempts were made to form flat glass on a bath of molten tin—one of the few liquids denser than glass that would be calm at the high temperatures needed to make glass—most notably in the US. Several patents were granted. Before the development of float glass, larger sheets of plate glass were made by casting a large puddle of glass on an iron surface, polishing both sides, a costly process. From the early 1920s, a continuous ribbon of plate glass was passed through a lengthy series of inline grinders and polishers, reducing glass losses and cost. Glass of lower quality, drawn glass, was made by drawing upwards from a pool of molten glass a thin sheet, held at the edges by rollers.
As it cooled the rising sheet stiffened and could be cut. The two surfaces were of lower quality i.e. not as uniform as those of float glass. This process continued in use for many years after the development of float glass. Between 1953 and 1957, Sir Alastair Pilkington and Kenneth Bickerstaff of the UK's Pilkington Brothers developed the first successful commercial application for forming a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity; the success of this process lay in the careful balance of the volume of glass fed onto the bath, where it was flattened by its own weight. Full scale profitable sales of float glass were first achieved in 1960. In 1964, CH3 Tank, the first purpose-built float line in the world, was built after the conversion of CH4 Tank. CH1 Tank closed down in 1977; the Pilkington's production line at Cowley Hill, St Helens, the birthplace of float glass, is no longer in operation as of 2014 although Pilkington continue to operate other float glass facilities within the town.
Float glass uses common glass-making raw materials consisting of sand, soda ash, dolomite and salt cake etc. Other materials may be used as colourants, refining agents or to adjust the physical and chemical properties of the glass; the raw materials are mixed in a batch process fed together with suitable cullet, in a controlled ratio, into a furnace where it is heated to 1500 °C. Common float glass furnaces are 9 m wide, 45 m long, contain more than 1200 tons of glass. Once molten, the temperature of the glass is stabilised to 1200 °C to ensure a homogeneous specific gravity; the molten glass is fed into a "tin bath", a bath of molten tin, from a delivery canal and is poured into the tin bath by a ceramic lip known as the spout lip. The amount of glass allowed to pour onto the molten tin is controlled by a gate called a tweel. Tin is suitable for the float glass process because it has a high specific gravity, is cohesive, is immiscible with molten glass. Tin, oxidises in a natural atmosphere to form tin dioxide.
Known in the production process as dross, the tin dioxide adheres to the glass. To prevent oxidation, the tin bath is provided with a positive pressure protective atmosphere of nitrogen and hydrogen; the glass flows onto the tin surface forming a floating ribbon with smooth surfaces on both sides and of thickness. As the glass flows along the tin bath, the temperature is reduced from 1100 °C until at 600 °C the sheet can be lifted from the tin onto rollers; the glass ribbon is pulled off the bath by rollers at a controlled speed. Variation in the flow speed and roller speed enables glass sheets of varying thickness to be formed. Top rollers positioned above the molten tin may be used to control both the thickness and the width of the glass ribbon. Once off the bath, the glass sheet passes through a lehr kiln for 100 m, where it is cooled so that it anneals without strain and does not crack from the temperature change. On exiting the "cold end" of the kiln, the glass is cut by machines. Today, float glass is the most used form of glass in consumer products.
Due to both its high quality with no additional polishing required and its structural flexibility d
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale, the photons can be said to follow Snell's Law. Translucency is a superset of transparency: it allows light to pass through, but does not follow Snell's law. In other words, a translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color; the opposite property of translucency is opacity. When light encounters a material, it can interact with it in several different ways; these interactions depend on the nature of the material. Photons interact with an object by some combination of reflection and transmission; some materials, such as plate glass and clean water, transmit much of the light that falls on them and reflect little of it.
Many liquids and aqueous solutions are transparent. Absence of structural defects and molecular structure of most liquids are responsible for excellent optical transmission. Materials which do not transmit light are called opaque. Many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of 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 or transmitted for our physical observation; this is. The attenuation of light of all frequencies and wavelengths is due to the combined mechanisms of absorption and scattering. Transparency can provide perfect camouflage for animals able to achieve it; this is easier in turbid seawater than in good illumination. Many marine animals such as jellyfish are transparent. With regard to the absorption of light, primary material considerations include: At the electronic level, absorption in the ultraviolet and visible portions of the spectrum depends on whether the electron orbitals are spaced such that they can absorb a quantum of light of a specific frequency, does not violate selection rules.
For example, in most glasses, electrons have no available energy levels above them in range of that associated with visible light, or if they do, they violate selection rules, meaning there is no appreciable absorption in pure glasses, making them ideal transparent materials for windows in buildings. At the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption, but because there is no molecular dipole moment. With regard to the scattering of light, the most critical factor is the length scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include: Crystalline structure: whether or not the atoms or molecules exhibit the'long-range order' evidenced in crystalline solids. Glassy structure: scattering centers include fluctuations in density or composition.
Microstructure: scattering centers include internal surfaces such as grain boundaries, crystallographic defects and microscopic pores. Organic materials: scattering centers include fiber and cell structures and boundaries. Diffuse reflection - Generally, when light strikes the surface of a solid material, it bounces off in all directions due to multiple reflections by the microscopic irregularities inside the material, by its surface, if it is rough. Diffuse reflection is characterized by omni-directional reflection angles. Most of the objects visible to the naked eye are identified via diffuse reflection. Another term used for this type of reflection is "light scattering". Light scattering from the surfaces of objects is our primary mechanism of physical observation. Light scattering in liquids and solids depends on the wavelength of the light being scattered. Limits to spatial scales of visibility therefore arise, depending on the frequency of the light wave and the physical dimension of the scattering center.
Visible light has a wavelength scale on the order of a half a micrometer. Scattering centers as small. Optical transparency in polycrystalline materials is limited by the amount of light, scattered by their microstructural features. Light scattering depends on the wavelength of the light. Limits to spatial scales of visibility therefore arise, depending on the frequency of the light wave and the physical dimension of the scattering center. For example, since visible light has a wavelength scale on the order of a micrometer, scattering centers will have dimensions on a similar spatial scale. Primary scattering centers in polycrystalline materi
Glass engraving is a form of decorative glasswork that involves engraving a glass surface or object. It is distinct from glass art in the narrow sense, which refers to moulding and blowing glass, from glass etching which uses acidic, caustic, or abrasive substances to achieve artistic effects; some artists may combine two or more techniques. There are several different types of glass engraving. Glass engraving is considered by many to be a dying art form. While this is far from accurate it is a form that has seen its heyday come and go. Despite this, there are still many glass engravers who are producing bold dynamic and aesthetically challenging artworks. In the UK one of the most notable artists is Alison Kinnaird MBE. Based in Scotland she splits her time between glass engraving and playing the traditional Scottish harp. In recent years these two disparate mediums have been combined when she composed music to accompany her piece "Psalmsong", now installed in the Scottish Parliament building.
The UK has a Guild of Glass engravers based in London and lists a number of well respected glass artists as members, including some overseas. These include Sally Scott, Tracey Sheppard, Dominic Fonde and Ronald Pennell, it has an online gallery of members works with contact details for commissions and classes for people who want to learn about this art. A general exhibition is held every two years; the most recent ones at the Fitzwilliam Museum in Cambridge 2010 and Stourbridge Red Cone galleries in 2012. Local branches in the UK meet for joint practical work and hold regional exhibitions. Meanwhile, the Czech republic having produced many world class glass artists can lay claim to one of the best, Jiri Harcuba; every two years the Czech Republic hosts a conference aimed at glass engravers. Other prolific notables around the world are Kevin Gordon in Australia and Lisabeth Sterling in the United States; some artists, such as Lesley Pyke, combine the art of drill engraving with sandblasting and sometimes acid etching as well.
All three techniques create different effects. An example of a relief illusion created from an intaglio cut form can be observed on this bowl engraved by Edmond Suciu, using the techniques of diamond and copper wheel engraving. Glass engraving encompasses a variety of techniques. One notable form is intaglio work, with images and inscriptions cut into the surface of the glass through abrasion. Glass engraving tools are therefore small abrasive wheels and drills, with small lathes used. Engraving wheels are traditionally made of copper, with a linseed oil and fine emery powder mixture used as an abrasive. Other forms of engraving are "stipple" and "drypoint" in which the surface of the glass is abraded with the use of small diamond tipped burrs; the scratches and small dots made in this method can, in the hands of a skilled artist, be used to produce images of astonishing clarity and detail. Notable practitioners of this form are James Dennison Pender and the late Lawrence Whistler who began a revival in England.
Sandblasting is yet another technique used in glass engraving. Abrasive is sprayed through a sandblasting gun on to glass, masked up by a piece of stencil in order to produce inscriptions; this is more of a commercial glass engraving technique employed by companies like Crystal Galleries Ltd in order to engrave on crystal awards and glass awards. Flashed glass Glass etching
An optical fiber is a flexible, transparent fiber made by drawing glass or plastic to a diameter thicker than that of a human hair. Optical fibers are used most as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires. Fibers are used for illumination and imaging, are wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors and fiber lasers. Optical fibers include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, while those that support a single mode are called single-mode fibers.
Multi-mode fibers have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters. Being able to join optical fibers with low loss is important in fiber optic communication; this is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the fiber cores, the coupling of these aligned cores. For applications that demand a permanent connection a fusion splice is common. In this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a mechanical splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors; the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics.
The term was coined by Indian physicist Narinder Singh Kapany, acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later. Tyndall wrote about the property of total internal reflection in an introductory book about the nature of light in 1870:When the light passes from air into water, the refracted ray is bent towards the perpendicular... When the ray passes from water to air it is bent from the perpendicular... If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be reflected at the surface.... The angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, while for diamond it is 23°42′.
In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. Practical applications such as close internal illumination during dentistry appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. In the 1930s, Heinrich Lamm showed that one could transmit images through a bundle of unclad optical fibers and used it for internal medical examinations, but his work was forgotten. In 1953, Dutch scientist Bram van Heel first demonstrated image transmission through bundles of optical fibers with a transparent cladding; that same year, Harold Hopkins and Narinder Singh Kapany at Imperial College in London succeeded in making image-transmitting bundles with over 10,000 fibers, subsequently achieved image transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled "A flexible fibrescope, using static scanning" was published in the journal Nature in 1954.
The first practical fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers. A variety of other image transmission applications soon followed. Kapany coined the term fiber optics, wrote a 1960 article in Scientific American that introduced the topic to a wide audience, wrote the first book about the new field; the first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, followed by the first patent application for this technology in 1966. NASA used fiber optics in the television cameras. At the time, the use in the cameras was classified confidential, employees handling the cameras had to be supervised by someone with an appropriate security clearance. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables were the first, in 1965, to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer, making fibers a practical communication medium.
They proposed th
The term stained glass can refer to coloured glass as a material or to works created from it. Throughout its thousand-year history, the term has been applied exclusively to the windows of churches and other significant religious buildings. Although traditionally made in flat panels and used as windows, the creations of modern stained glass artists include three-dimensional structures and sculpture. Modern vernacular usage has extended the term "stained glass" to include domestic lead light and objects d'art created from foil glasswork exemplified in the famous lamps of Louis Comfort Tiffany; as a material stained glass is glass, coloured by adding metallic salts during its manufacture. The coloured glass is crafted into stained glass windows in which small pieces of glass are arranged to form patterns or pictures, held together by strips of lead and supported by a rigid frame. Painted details and yellow stain are used to enhance the design; the term stained glass is applied to windows in which the colours have been painted onto the glass and fused to the glass in a kiln.
Stained glass, as an art and a craft, requires the artistic skill to conceive an appropriate and workable design, the engineering skills to assemble the piece. A window must fit snugly into the space for which it is made, must resist wind and rain, especially in the larger windows, must support its own weight. Many large windows have withstood the test of time and remained intact since the Late Middle Ages. In Western Europe they constitute the major form of pictorial art to have survived. In this context, the purpose of a stained glass window is not to allow those within a building to see the world outside or primarily to admit light but rather to control it. For this reason stained glass windows have been described as "illuminated wall decorations"; the design of a window may be figurative. Windows within a building may be thematic, for example: within a church – episodes from the life of Christ. Stained glass is still popular today, but referred to as art glass, it is prevalent in luxury homes, commercial buildings, places of worship.
Artists and companies are contracted to create beautiful art glass ranging from domes, backsplashes, etc. During the late medieval period, glass factories were set up where there was a ready supply of silica, the essential material for glass manufacture. Silica requires a high temperature to melt, something not all glass factories were able to achieve; such materials as potash and lead can be added to lower the melting temperature. Other substances, such as lime, are added to rebuild the weakened network and make the glass more stable. Glass is coloured by adding metallic oxide powders or finely divided metals while it is in a molten state. Copper oxides produce green or bluish green, cobalt makes deep blue, gold produces wine red and violet glass. Much modern red glass is produced using copper, less expensive than gold and gives a brighter, more vermilion shade of red. Glass coloured while in the clay pot in the furnace is known as pot metal glass, as opposed to flashed glass. Using a blow-pipe, a "gather" of molten glass is taken from the pot heating in the furnace.
The gather is formed to a bubble of air blown into it. Using metal tools, molds of wood that have been soaking in water, gravity, the gather is manipulated to form a long, cylindrical shape; as it cools, it is reheated. During the process, the bottom of the cylinder is removed. Once brought to the desired size it is left to cool. One side of the cylinder is opened, it is put into another oven to heat and flatten it, placed in an annealer to cool at a controlled rate, making the material more stable. "Hand-blown" cylinder and crown glass were the types used in ancient stained-glass windows. Stained glass windows were in churches and chapels as well as many more well respected buildings; this hand-blown glass is created by blowing a bubble of air into a gather of molten glass and spinning it, either by hand or on a table that revolves like a potter's wheel. The centrifugal force causes the molten bubble to flatten, it can be cut into small sheets. Glass formed this way can be either coloured and used for stained-glass windows, or uncoloured as seen in small paned windows in 16th- and 17th-century houses.
Concentric, curving waves are characteristic of the process. The center of each piece of glass, known as the "bull's-eye", is subject to less acceleration during spinning, so it remains thicker than the rest of the sheet, it has the distinctive lump of glass left by the "pontil" rod, which holds the glass as it is spun out. This lumpy, refractive quality means the bulls-eyes are less transparent, but they have still been used for windows, both domestic and ecclesiastical. Crown glass is still made today, but not on a large scale. Rolled glass is produced by pouring molten glass onto a metal or graphite table and rolling it into a sheet using a large metal cylinder, similar to rolling out a pie crust; the rolling can be done by machine. Glass can be "double rolled", which means it is passed through two cylinders at once to yield glass of a specified thickness (typically about 1/8" or
Enamelled glass is glass, decorated with vitreous enamel and fired to fuse the glasses. It can produce brilliant and long-lasting colours, be transparent, translucent or opaque; the desired colours only appear when the piece is fired, adding to the artist's difficulties. It is similar to vitreous enamel on metal surfaces, it is close to "enamelled" overglaze decoration on pottery on porcelain, it is thought that the technique passed from metal to glass, in the Renaissance from glass to pottery. Glass may be enamelled by sprinkling a loose powder on a flat surface, painting or printing a slurry, or painting or stamping a binder and sprinkling it with powder, which will adhere; as with enamel on metal, gum tragacanth may be used to make sharp edges. Some modern techniques are much simpler than historic ones. For instance, there now exist glass enamel pens. Enamelled glass is used in combination with gilding. Mica may be added for sparkle. Enamelled Venetian glass was called smalto. Mosque lamps are made of enamelled glass.
They have lugs, from which they are suspended to light not only mosques, but similar spaces such as madrassas and mausoleums. They have a religious symbolism based on the Quranic verse of light, with which they are calligraphed. During the European Renaissance, expensive enamelled goblets were used as courtship and marriage gifts; these goblets were used, some have survived. Glass painting involves painting with glass, making the finished work transparent. Glass fusing is similar. List of some surviving medieval enamelled glass Vitreous enamel Damascening Enamel cloisonné Plique-à-jour Champlevé Basse-taille Other techniques of artistic enameling Painted glass Glass fusing Fused glass Photosensitive glass Islamic glass Venetian glass
Rippled glass refers to textured glass with marked surface waves. Louis Comfort Tiffany made use of such textured glass to represent, for example, water or leaf veins; the texture is created during the glass sheet-forming process. A sheet is formed from molten glass with a roller; the roller spins at the same speed as its own forward motion, the resulting sheet has a smooth surface. In the manufacture of rippled glass, the roller spins faster than its own forward motion; the rippled effect is retained. In order to cut rippled glass, the sheet may be scored on the smoother side with a carbide glass cutter, broken at the score line with breaker-grozier pliers. Architectural glass Beveled glass Came glasswork Cathedral glass Drapery glass Fracture glass Fracture-streamer glass Ring mottle glass Stained glass Streamer glass