Glass | Research & Encyclopedia Articles

Glass

Glass, given its durability and versatility, plays an important role in human culture. Generally manufactured by heating sand (silica), soda (alkali), lime, and other ingredients at high temperature, glass is a fundamental component of a variety of products, including tableware, windshields, thermometers, and telescope lenses. Early peoples were likely to have discovered natural glass, which is created when lightning strikes sand, and were certain to have used obsidian--a dark volcanic glass--for weapons, ornaments, and money. The first manmade glass probably took the form either of glass beads or ceramic glaze and appeared around 4000 to 5000 b.c. Surviving examples of Egyptian and Mesopotamian glass objects date to around 1550 b.c. For centuries glass, shaped by the use of molds, remained costly and difficult to produce. The invention of the blowpipe method of glassmaking (in which molten glass is puffed into shape with the use of a hollow tube) in about 30 b.c. made glass more commonplace. Typical uses at the time included windows as well as decorative objects. The first four centuries a.d. are sometimes referred to as the First Golden Age of glassmaking, for during this period artisans produced a wide variety of artifacts that are now highly valued. After the decline of the Roman Empire, few developments took place in European glassmaking until the twelfth and thirteenth centuries, when stained glass windows (formed of pieces of colored glass outlined by lead strips and assembled into a narrative picture) began to appear in English and French churches. During the Crusades, Europeans were exposed to the accomplished glassmaking of the Near East, an influence evidenced by the growth of the craft in Italy, particularly Venice. Beginning around 1300, the Venetians ushered in the Second Golden Age of glassmaking; they became widely known for a particularly transparent glass that was worked into a number of delicate objects. In the late 1400s and 1500s the Germans and other northern Europeans were producing containers and drinking vessels that differed markedly in their utilitarian value from those produced by the Venetians. Nonetheless, Venetian glass was immensely popular during the reign of Queen Elizabeth I (1558-1603). In 1674, George Ravenscroft brought fame to English glassmaking when he invented lead glass (now usually called lead crystal), an especially brilliant glass he produced accidentally when he added lead oxide to his mixture instead of lime. In colonial America, the glass made by this technique became known as flint glass, and was usually etched or cut into facets to lend it additional luster. The first glass plant in the United States was built at Jamestown, Virginia, in 1608, but it survived for less than a year. Much later, in 1739, Caspar Wistar successfully launched the American glass industry with a plant in Salem City, New Jersey. Other prominent figures in early American glassmaking included Henry William "Baron" Stiegel and John F. Amelung. The renowned Sandwich glass that is now much coveted by American collectors was made by the Boston and Sandwich Glass Company; the Bakewell Company of Pittsburgh was another famous glass manufacturer. The early 1800s saw a tremendous demand for glass windows, which were a symbol of affluence, particularly in the frontier communities of America. Window glass was originally made by spinning out a bubble of blown glass until it became flat; because of the bump or "crown" that was invariably left in its center, this was called crown glass. Around 1825, the cylinder process replaced the earlier method. Now the glass was blown into a cylinder shape that, when cooled, was cut down one side; when reheated, the cylinder flattened out to form a sheet. In 1842, John J. Adams invented a more sophisticated glass-flattening and tempering process that made not only plate glass but mirrors, showcases, and other products more widely available. During the last half of the nineteenth century, glass found wide use in medicinal containers, tableware, and kerosene lamps. Tempered glass (made exceptionally strong through a reheating process) was invented by François Royer de la Bastie in 1874, and wire glass (industrial sheet glass with metal mesh laminated into it) by Leon Appert in 1893. In 1895, Michael J. Owens invented a bottle-making machine that allowed bottled drinks to be produced inexpensively.

The great technological advances of the twentieth century broadened the range of ingredients, shapes, uses, and manufacturing processes for glass. Natural gas replaced the wood and coal that had previously been used in the glassmaking process, and huge operations were established. One of the most common forms of glass now produced is flat glass, used for windows, doors, and furniture. Formed by flattening melted glass between rollers, annealing (heat treating) in an oven called a lehr, then cutting into sheets and grinding and polishing until smooth, this category includes sheet glass and the higher quality plate glass. The best quality of all is achieved in float glass, invented in 1952 by Alistair Pilkington. Float glass is made by floating a ribbon of liquefied glass on top of molten tin so that it forms a perfectly even layer; the result is glass with a brilliant finish that requires no grinding or polishing.

In 1957, Donald Stookey of Corning Glass Works discovered that the addition of certain nucleating agents to Fotoform glass (used in electronic components and fluidic control devices) produced glass objects that could be transformed into fine-grained ceramics by heat treatment. This new Pyroceram composition became the basis of Corning Ware, first marketed in 1958. In 1964, Corning announced the invention of photochromic glass, which darkens under ultraviolet light and then clears when removed from the light source.

In 1980, Pilkington invented kappafloat glass, which features a special, energy-efficient glaze that traps thermal heat while allowing solar heat to filter through. Other modern forms of glass include the laminated safety glass used for automobile windows, which is composed of sandwiched layers of plastic and glass; fused silica optical waveguides (optical fibers used for long distance telecommunication); nonreflecting glass (invented by Katherine Burr Blodgett and others); structural glass, used in buildings; heat-resistant cookware such as Pyrex; and fiberglass.