A hard, brittle, translucent, and commonly transparent substance, white or coloured, having a conchoidal fracture, and made by fusing together sand or silica with lime, potash, soda, or lead oxide. It is used for window panes and mirrors, for articles of table and culinary use, for lenses, and various articles of ornament.
Glass is variously coloured by the metallic oxides; thus, manganese colours it violet; copper (cuprous), red, or (cupric) green; cobalt, blue; uranium, yellowish green or canary yellow; iron, green or brown; gold, purple or red; tin, opaque white; chromium, emerald green; antimony, yellow.
Other Glass definitions
Glass is much used adjectively or in combination; as, glass maker, or glassmaker; glass making or glassmaking; glass blower or glassblower, etc. Bohemian glass, Cut glass, etc.
Crown glass, a variety of glass, used for making the finest plate or window glass, and consisting essentially of silicate of soda or potash and lime, with no admixture of lead; the convex half of an achromatic lens is composed of crown glass; so called from a crownlike shape given it in the process of blowing.
Crystal glass, or Flint glass. See Flint glass, in the Vocabulary. Cylinder glass, sheet glass made by blowing the glass in the form of a cylinder which is then split longitudinally, opened out, and flattened. Glass of antimony, a vitreous oxide of antimony mixed with sulphide.
Glass blower, one whose occupation is to blow and fashion glass.
Glass blowing, the art of shaping glass, when reduced by heat to a viscid state, by inflating it through a tube. Glass cloth, a woven fabric formed of glass fibres.
Glass cutter. One who cuts sheets of glass into sizes for window panes, ets. One who shapes the surface of glass by grinding and polishing. A tool, usually with a diamond at the point, for cutting glass.
Glass cutting. The act or process of dividing glass, as sheets of glass into panes with a diamond. The act or process of shaping the surface of glass by appylying it to revolving wheels, upon which sand, emery, and, afterwards, polishing powder, are applied; especially of glass which is shaped into facets, tooth ornaments, and the like.
Archaeological evidence indicates that glass was first made in the Middle East, sometime in the 3rd millennium BC.
The earliest glass objects were beads; hollow vessels do not occur before about 1500 BC. Asian artisans may have established the glass industry in Egypt, where the first vessels date from the reign (1504-1450 BC) of Thutmose III. Glass production flourished in Egypt and Mesopotamia until about 1200 BC, then virtually ceased for several hundred years. In the 9th century BC, Syria and Mesopotamia emerged as glassmaking centres, and the industry spread throughout the Mediterranean region. In the Hellenistic era, Egypt, because of the glassworks at Alexandria, assumed a leading role in supplying royal courts with luxury glass. It was on the Phoenician coast, however, that the important discovery of glassblowing occurred in the 1st century BC. In the Roman period glassmaking was undertaken in many areas of the empire, from Rome to Cologne.
Before the invention of the blowpipe, several methods existed for shaping and embellishing objects of coloured glass, both translucent and opaque. Some articles were carved from solid blocks of glass. From potters and metalworkers glassmakers adapted casting processes, pouring molten glass into moulds to produce inlays, statuettes, and vessels such as jars and bowls. Preformed rods of glass could be heated and fused together in a mould to make "ribbon" glass. Patterns of great complexity were produced by a mosaic technique, in which elements, fused in a rod, together made a design in cross section. Slices of such rods could be arranged in a mould to shape a vessel or plaque and then heated to fusion. "Gold band" glasses featured irregular bands of different-coloured glass, with gold leaf embedded in one translucent band.
Most pre-Roman glassware was fashioned by the core technique. A mixture of clay and dung was fixed to a metal rod and given the shape of the desired vessel. It was dipped into a crucible of molten glass or was wound with threads of glass. The object was constantly reheated and smoothed on a flat stone. Threads of different-coloured glass were trailed on and combed, creating striking feather patterns, as seen on Egyptian glass of the 18th and 19th dynasties. Handles, feet, and the neck were added. When the object had cooled the rod was withdrawn and the core material picked out. Only vessels of limited size, such as cosmetic containers and small vases, could be made in this way. Later core-formed articles from the 6th century BC closely followed the forms of Greek pottery.
Glassblowing, a less expensive and time-consuming method of manufacture, spread from Syria to Italy and other parts of the Roman Empire, gradually superseding older techniques. A new taste in glass styles developed: the earlier manufacturing processes emphasized colour and pattern; blowing enhanced the thin, translucent qualities of the material. Also, by the end of the 1st century AD, colourless glass had become more fashionable than coloured glass. Glassblowing made large-scale production possible and changed the status of glassware to an everyday material, used for windows, drinking vessels, and containers of all kinds.
The structure of the Roman Empire doubtless fostered the extraordinary developments in glassmaking that occurred in this period. Most of the known decorative techniques were invented by artisans of the Roman era. Blown glassware was patterned in moulds, which enabled such novelty items as head-shaped flasks to be produced in quantity. Some Roman glass has elaborately threaded and tooled decoration. Glasswares could be painted with religious and historical scenes, or could feature designs in gold leaf pressed between two layers of clear glass.
Ancient glassmakers adapted lapidary skills to make lathe-cut, carved, and engraved glass of considerable beauty. In cameo glass, layers of different coloured glass were fused together and then carved so as to leave contrasting motifs in relief. The most famous example of Roman cameo glass is the Portland Vase (1st century AD, British Museum, London), which illustrates the myth of Peleus and Thetis. Delicate effects were achieved in the diatreta, or caged cups, in which great portions of the outer surface were cut away, leaving an intricate openwork frame that appears to stand almost free of the vessel within. The famous Lycurgus Cup (4th century AD, British Museum) epitomizes this practice.
With the fall of the Roman Empire, the manufacture of household glass suffered a general decline in the West.
Under Frankish influence glassmakers in Britain and northern Europe continued to produce utilitarian vessels, some taking new, robust forms. The decoration of these objects was limited to simple moulded patterns, threading, and applied ornaments such as prunts (blobs of glass). The glass, mostly a greenish colour, was at first a soda-glass composition made with ashes of marine plants imported from the Mediterranean, as they had been during Roman times. By the late Middle Ages, however, soda was no longer available, and northern glassmakers turned to the wood ash from their own wood-fired furnaces as a flux; this produced potash-lime glass. Because the glasshouses were situated in the forests that provided fuel and ash, the glass made was called waldglas (forest glass). Common glass in the waldglas style continued to be made in the lesser European factories until modern times.
The glory of Western glassmaking in the medieval period, through the patronage of the Church, was mosaic glass in Mediterranean Europe and stained-glass windows in the north. Mosaics were made of small glass cubes, or tesserae, embedded in cement. The tesserae, cut from solid cakes of glass, could be extremely elaborate, with gold and silver lead inlaid. Little is known of the production of mosaic glass before the 14th century.
Glass windows in churches are mentioned in documents as early as the 6th century, but the earliest extant examples date from the 11th century. The finest windows are considered those from the 13th and 14th centuries, primarily in France and England. Glasshouses in Lorraine and Normandy may have provided much of the flat glass for medieval cathedral windows. The glass was coloured, or flashed with colour, and then cut into the shapes required by the design. Details were painted into the glass, often with a brownish enamel. The pieces were fitted into lead strips and set in an iron framework. This art declined in the late Renaissance but was revived in the 19th century.
Although glassmaking was practised in Venice from the 10th century onwards, the earliest known Venetian glassware dates from the 15th century. Concentrated on the island of Murano, the Venetian industry dominated the European market until 1700. The major contribution of the Venetians was the development of a highly refined, hard-soda glass of great ductility. Colourless and highly transparent, the glass resembled rock crystal and was known as cristallo.
The first cristallo wares were simple forms, often embellished with jewel-like enamel designs. Objects were also blown from coloured and opaque glass. By the late 16th century, forms became lighter and more delicate. The blowers exploited the workable nature of their material to produce fanciful tours de force. A type of filigree glass was developed in Venice and widely imitated. With lacelike effect, opaque white threads were incorporated in the glass and worked into intricate patterns. Some vessels were blown entirely from opaque white glass and painted with enamels in the manner of Chinese porcelain. Novelties made of lampworked glass were made at Murano, but by the 17th century Nevers, France, became most famous for this type of ware. Particularly suited to soda glass was the practice of diamond-point engraving, a technique favoured in the 17th century by Dutch artisans. Hammering the glass with a diamond-pointed stylus produced a stippled effect, and ambitious pictorial designs were created.
Glass manufacturers throughout Europe tried to copy Venetian production methods, materials, and decorative vocabulary. Knowledge was spread through the glassware itself, through the Art of Glass (1612) by Antonio Neri, and through Venetian glassblowers working abroad. Although forbidden by law to leave Venice and to divulge the secrets of their craft, many Murano glassmakers left Italy to set up glasshouses elsewhere in Europe. Each country developed its own façon de Venise glassware (as Venetian-style glassware had become known), as nationalistic preferences for certain forms or decorations modified the Venetian model.
Italy's supremacy was ultimately weakened in the 17th century by the development of new glass recipes in Germany and England. Germany's potash-lime glass, thicker and harder than cristallo, was well suited to wheel-engraved decoration. Caspar Lehmann, at the court of the Holy Roman Emperor, Rudolf II, in Prague, was largely responsible for the development of engraving in the early 1600s. Glasscutters and engravers in Nuremberg and Potsdam became famous for skilfully executed designs in the Baroque style. At the same time, the Germanic glasshouses continued their tradition of enamelled and cold-painted glass.
The other improvement in glass that served to diminish Europe's reliance on Venice was the lead-oxide glass formulated (c. 1676) by George Ravenscroft in England. Softer, more brilliant, and more durable than the brittle cristallo, English lead glass was considered the finest glass of the 18th century. English table glass dominated the European and colonial markets and became a model for Continental production. English innovations of the mid-18th century were glasses with air or opaque-enamel twists encased in the stems. Among the most prestigious forms of the period was the English cut-glass chandelier. Lead glass, especially suited to cutting, reached its apogee in Anglo-Irish Neo-Classical glassware made between 1780-1830.
Glassmaking was the first manufacturing industry to be established in America. A glasshouse was built at Jamestown, Virginia, in 1608. The first commercially successful glassworks was that of Caspar Wistar in Salem County, New Jersey, between 1739 and 1777. Immigrant German artisans there and at other factories produced bottles, window glass, and some table glass in Germanic styles.
Henry William Stiegel sought to imitate English imported lead glass at his factory in Lancaster County, Pennsylvania, from 1763 to 1774. The most important glassworks built after the American War of Independence was that of John Frederick Amelung in Frederick County, Maryland, which was in operation from 1784 to 1795.
The stylistic history of glass in the 19th century is dominated by rapid advances in glass technology and by the rediscovery and adaptation of older methods.
Mechanical pressing was a cheap, swift means of production that greatly expanded the role of glass in the home and in industry. Before 1850, wares were pressed in intricate lacy designs that offset a cloudiness in the glass caused by contact with the cooler mould. Simpler designs popular from the 1840s on, known as pressed pattern glass, were available in many forms. The more expensive cut glass declined in popularity because of the competition from pressed glass. Only in about 1880 did cut glass regain some of its earlier popularity with the elaborate "brilliant" patterns, examples of great technical virtuosity that exploited the refractive properties of quality glass.
Beginning in the late 18th century, a number of Roman glassmaking techniques were revived and modified to suit Neo-Classical taste. Continental glass factories made a version of laminated gold-leaf glass, called zwischengoldglas. Cameolike effects were obtained through the use of encrusted sulphides, and from the mid-19th century actual cameo engraving and cutting were practised by artisans, culminating in the work of Thomas Webb and Sons (founded 1837), a glasshouse in Stourbridge, England. Paperweights, popular from about 1845, were often made in a millefiori (thousand flowers) design recalling the mosaic glass of ancient times. In the late 19th century Renaissance rock crystal inspired a technique of polished engraved glass.
Bohemia continued to excel in wheel-engraved decoration with the work of such artisans as Dominik Biemann. Other methods, such as those for producing cased glass, were practised in Bohemian factories and copied throughout Europe and the United States. Chemical advancements led to new opaque coloured glass such as lithyalin, which resembled semiprecious stones. Transparent enamels and stains were applied to vessels, paralleling the revival of stained-glass windows.
By 1880, inspired by the revivals of historical glassworking methods and spurred by the capabilities of improved chemical technology, glassmakers were creating new styles of handworked glass, generally called art glass. These were mostly decorative and novelty forms, made in reaction to mass-produced wares. Between 1890 and 1910 the most fashionable styles reflected the international Art Nouveau movement. Louis Comfort Tiffany in the United States, and Émile Gallé and the firm of Daum Frères (founded 1889) in France, were the leading exponents of the style. They produced glassware in naturalistic shapes, with sinuous lines, exotic colours, and unusual surface effects, such as Tiffany's iridescent Favrile glass.
After World War I new interests in texture and formalized decoration emerged, as seen in the designs of René Lalique and Maurice Marinot. From the 1930s, exquisitely clear, colourless lead glass, often engraved, was popularized by several Scandinavian and American firms.
A new era in glassmaking began in the early 1960s with the studio glass movement, led by the Americans Harvey Littleton and Dominick Labino. With small tank furnaces in studio settings, artisans explore glass as an artistic medium. Innovative sculptural forms and decorative techniques are being developed at workshops around the world.
A glass is an inorganic non metallic material that does not have a crystalline structure. Such materials are said to be amorphous and are virtually solid liquids cooled at such a rate that crystals have not been able to form.
Typical glasses range from the soda-lime silicate glass for soda bottles to the extremely high purity silica glass for optical fibers. Glass is widely used for windows, bottles, glasses for drinking, transfer piping and recepticles for highly corrosive liquids, optical glasses, windows for nuclear applications etc. etc.
In history most products have been blown glass. In recent times most flat glass has been produced using the float process. Mass produced bottles and decorative products are made using industrial scale blown glass process. Hand blown glass items are made in art/craft centers throughout the world.
The main constituent of glass is silicon dioxide (SiO 2). The most common form of silica used in glassmaking has always been sand.
Sand by itself can be fused to produce glass but the temperature at which this can be achieved is about 1700o C. Adding other chemicals to sand can considerably reduce the temperature of the fusion. The addition of sodium carbonate ( Na 2 CO 3), known as soda ash,in a quantity to produce a fused mixture of 75% Silica (SiO 2) and 25% of sodium oxide (Na 2O), will reduce the temperature of fusion to about 800o C. However, a glass of this composition is water soluble and is known as water glass. In order to give the glass stability, other chemicals like Calcium Oxide (CaO) and magnesium oxide (MgO) are needed. The raw materials used for introducing CaO and MgO are their carbonates, limestone (CaCO 3) and dolomite (MgCO3), which when subjected to high temperatures give off carbon dioxide leaving the oxides in the glass.
Glasses may be devised to meet almost any imaginable requirement. For many specialised applications in chemistry, pharmacy, the electrical and electronics industries, optics, the construction and lighting industries, glass, or the comparatively new family of materials known as glass ceramics, may be the only practical material for the engineer to use.
Each can be made by a suitable adjustment to chemical compositions, but the main types of glass are:
Most of us are more familiar with this type of glass in the form of ovenware and other heat-resisting ware. Borosilicate glass, the third major group, is made mainly of silica (70-80%) and boric oxide (7-13%) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminium oxide.
This type of glass has a relatively low alkali content and consequently has good chemical durability and thermal shock resistance (it doesn't break when changing temperature quickly.)
As a result it is widely used in the chemical industry, for laboratory apparatus, for ampoules and other pharmaceutical containers, for various high intensity lighting applications and as glass fibres for textile and plastic reinforcement.
Most of the glass we see around us in our everyday lives in the form of bottles and jars, flat glass for windows or for drinking glasses is known as commercial glass or soda-lime glass, as soda ash is used in its manufacture.
The main constituent of practically all commercial glass is sand. Sand by itself can be fused to produce glass but the temperature at which this can be achieved is about 1700°C. Adding other minerals and chemicals to sand can considerably reduce the melting temperature.
The addition of sodium carbonate (Na2CO3), known as soda ash, to produce a mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O), will reduce the temperature of fusion to about 800°C. However, a glass of this composition is water-soluble and is known as water glass. In order to give the glass stability, other chemicals like calcium oxide (CaO) and magnesium oxide (MgO) are needed. These are obtained by adding limestone which results in a pure inert glass.
Commercial glass is normally colourless, allowing it to freely transmit light, which is what makes glass ideal for windows and many other uses. Additional chemicals have to be added to produce different colours of glass such as green, blue or brown glass.
Glass fibre has many uses from roof insulation to medical equipment and its composition varies depending on its application.For building insulation and glass wool the type of glass used is normally soda lime. For textiles, an alumino-borosilicate glass with very low sodium oxide content is preferred because of its good chemical durability and high softening point. This is also the type of glass fibre used in the reinforced plastics to make protective helmets, boats, piping, car chassis, ropes, car exhausts and many other items.In recent years, great progress has been made in making optical fibres which can guide light and thus transmit images round corners.
These fibres are used in endoscopes for examination of internal human organs, changeable traffic message signs now on motorways for speed restriction warnings and communications technology without which telephones and the internet would not be possible.
Commonly known as lead crystal, lead glass is used to make a wide variety of decorative glass objects.It is made by using lead oxide instead of calcium oxide, and potassium oxide instead of all or most of the sodium oxide. The traditional English full lead crystal contains at least 30% lead oxide (PbO) but any glass containing at least 24% PbO can be described as lead crystal. Glass containing less than 24% PbO, is known simply as crystal glass.
The lead is locked into the chemical structure of the glass so there is no risk to human health.Lead glass has a high refractive index making it sparkle brightly and a relatively soft surface so that it is easy to decorate by grinding, cutting and engraving which highlights the crystal's brilliance making it popular for glasses, decanters and other decorative objects.
Glass with even higher lead oxide contents (typically 65%) may be used as radiation shielding because of the well-known ability of lead to absorb gamma rays and other forms of harmful radiation.
Glassmaking involves two main steps, heating and mixing raw materials to produce molten glass, and forming the molten glass into the desired shape. Most glass then receives further treatment to produce the final product.
Glass manufacture begins with the careful selection and measurement of raw materials. The most important raw material is sand. Other raw materials used depend on the type of glass being made. Broken glass, called cullet, is usually added to the raw materials. It promotes the melting of the raw materials as they are heated.
Most cullet is waste from glass-forming operations; some is obtained from recycled glass products. The raw materials and cullet are heated until they have melted into a spongy mass full of bubbles.
The temperature of the melt is then increased to make it more fluid, allowing the bubbles to rise to the surface and escape. The glass at this stage is clear and homogeneous. When the glass is withdrawn from the furnace its viscosity is too low for it to hold any form. As the glass is cooled, it flows less easily and can be formed. This is done using one of the following processes: machine blowing, drawing, floating, pressing, or rolling.
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