Uses of glass

“Glass” commonly describes materials rich in silicon dioxide that are produced by solidification from the molten state without crystallizing. Glass’s many valuable qualities have made it one of the most widely used materials in the world, with applications ranging from windows to optical instruments to electronics.

Background

Glass, although a commonplace material for centuries, is an exceptional substance: It is a solid that is technically considered a liquid. All other familiar solids are crystalline in structure. That is, they possess a definite, orderly internal geometric form that is a reflection of the arrangement of their constituent atoms. Their atoms are packed in repetitive forms called networks or lattices. Liquids, in contrast, are termed amorphous in structure. They lack the rigid, repeating internal structure of solids. Glasses can be considered a borderline case between classic solids and liquids, and they have been called “amorphous solids.”

Glasses are considered to be “supercooled” liquids—liquids chilled so rapidly that they never undergo the process of true solids. When a solid’s molecules cool down from a molten state, the material undergoes a series of internal dynamic changes in response to the loss of heat. Molecules move in a more rigid fashion until reaching a point at which their patterns of movement and their interatomic bonds reach a state of discontinuity. This point of discontinuity is commonly called the freezing point of the solid; at this point it begins rapidly to lock into the pattern of crystallinity. Liquids, such as glasses, never actually reach this point of discontinuity and are considered to be in a “metastable” state. Glasses, besides possessing liquid structures, are typically also solutions; that is, they are composed of homogenous mixtures of substances possessing dissimilar molecular structures. The primary constituent of most common glass is silica, or silicon dioxide (SiO₂). Soda (sodium oxide), lime (calcium oxide), and small amounts of many other possible materials, including boron oxide, aluminum oxide, and magnesium oxide, are also used in the making of sand.

The properties of glass can be modified by industrial processes to suit various uses, but in general these properties include a generally excellent resistance to chemical corrosion; a high resistance to heat; an outstanding ability to insulate against electrical current, even at high voltages; high surface smoothness; good scratch resistance; a high ratio of weight to strength, coupled with a tendency toward brittleness; radiation absorbance and sensitivity; and a range of optical properties that include the ability to disperse, refract, or reflect light. All the foregoing properties have made various forms of glass a preferred material for numerous applications.

Ingredients and Manufacturing

Silica—in the form of sand that is processed and cleaned before use—is the primary ingredient in almost all glass. In addition, the common glass that is generally used in such items as bottles, drinking glasses, lightbulbs, and window glass (sheet glass) contains soda (Na₂O), which makes the glass easier to work with in manufacturing, and lime (CaO), which overcomes weaknesses introduced by the soda. A wide range of other materials may be used in small amounts, among them aluminum and magnesium oxide. The three most common types of glass are soda-lime glass, borosilicate glass, and lead glass. Lead glass, used in optics and “crystal” tableware, is soda-lime glass to which lead oxide is added to provide exceptional clarity and refractivity. Boron oxide is added in the production of borosilicate glass, used in kitchenware (such as Pyrex) and laboratory ware because it resists breakage during rapid temperature changes.

Both window glass (sheet glass) and plate glass are soda-lime glass, but their manufacturing processes are different. Window glass, for example, is cooled, flattened into shape by rollers, then finished and cut into standard sizes. The manufacture of plate glass is more complex; the glass is strengthened by annealing, then ground smooth and polished. Plate glass is stronger and has less distortion than window glass. Safety glass, or laminated glass, as used in automobile windshields, generally contains a layer of plastic between two layers of glass to keep the glass from shattering completely upon impact.

History

The production of synthetic glass has a long history. In fact, aside from metallurgy, glassmaking can be considered the oldest of industrial arts practiced by early civilizations. The use of natural high-silica minerals having glasslike properties, such as obsidian (produced by volcanic action and sometimes called volcanic glass), is even older. It can be traced many tens of thousands of years into prehistory back to the early Paleolithic era (the Old ). Early humans and even protohominids made tools and weapons by “flintknapping”: shaping obsidian and obsidian-like rocks and minerals by percussion and pressure flaking. These materials were artfully manipulated; prehistoric artisans took advantage of the natural tendency of glasses to be brittle and to break at the surface into chonchoidal fractures (arcuate shapes). Blades, chisels, awls, gouges, and other implements could be produced in this way.

The earliest artificial glass was produced at least three thousand years ago in Egypt for decorative purposes. Colored glazes were fired onto pottery or stone beads and other objects, originally in imitation of the surface colors and lusters of precious and semiprecious stones. Eventually, experimentation led to the development of freestanding, three-dimensional glass objects such as vials and bottles. This development is believed to have occurred in Egypt around 1500 BCE during the New Kingdom period. Eventually, much higher transparency and ease of fabrication evolved with the discovery of the art of glassblowing, circa 50 BCE, in the area of Phoenicia (modern coastal Lebanon). Glassmaking and glassblowing spread rapidly throughout the Mediterranean world with the expansion of the Roman Empire but declined with the waning of the Roman civilization. Glassmaking centers survived in the Middle East and other areas. Eventually, glassmaking experienced a resurgence in Europe beginning in the eleventh century, and new techniques and glass compositions were developed. Glass technology continued to improve gradually until the nineteenth century, when it experienced rapid improvements because of the increasing needs of science and the new industries spawned by the Industrial Revolution. Experimenters such as Michael Faraday contributed greatly to the understanding of the physics and chemistry of glass during the nineteenth century. A glassblowing machine had been developed by the 1890s, and automated machines were producing molded and blown glass items in the early twentieth century. The growing demands of science and industry in the twentieth century engendered the production of glasses of increasingly sophisticated composition and fabrication.

Uses of Glass

The earliest use of synthetic glass seems to have been in the form of decorative or artistic objects, including jewelry. Glass is still considered an artistic medium and an attractive material for decoration; it is used in sculpture, stained glass windows, vases, vials, jewelry, and mirrors. Particularly beginning with the Industrial Revolution, however, glass has been much more extensively used in the form of utilitarian objects and devices. Plate glass, sheet glass, and wired glass are found in virtually every modern building and vehicle, whether automobile, boat, or aircraft. Countless glass bottles and jars are used in every country to store and transport liquids of all sorts. Lighting fixtures in the form of incandescent and fluorescent lightbulbs and tubes are one of the most familiar modern uses of glass, and they number in the billions. Hundreds of millions of glass cathode-ray tubes (CRTs) are found worldwide in the form of television sets and video display terminals (VDTs) for personal computers. Military and civilian applications of optical-quality glass elements in the form of magnifying lenses for microscopes, telescopes, binoculars, periscopes, prisms, and other eyepieces also number in the millions and are in use on land, at sea, and in the air. Structural insulation in the form of glass fiber mats is a commonly manufactured good produced from fine, woollike glass fibers.

Chemistry and physics laboratories use glass extensively in the form of piping, tubes, rods, storage vessels, vacuum flasks, and beakers. Some of the more sophisticated recent uses of glass are in the telecommunications industry. Optical fibers (or fiber optics) are very fine, flexible, high-quality glass strands designed to transmit signals in the form of light impulses.

Bibliography

Doremus, Robert H. Glass Science. 2d ed. New York: Wiley, 1994.

Frank, Susan. Glass and Archaeology. New York: Academic Press, 1982.

Kelleher, Katy. "The Strange Life of Glass." Nautilus, 25 Apr. 2023, nautil.us/the-strange-life-of-glass-299761/. Accessed 29 Dec. 2024.

Macfarlane, Alan, and Gerry Martin. Glass: A World History. Chicago: University of Chicago Press, 2002.

Shackelford, James F., and Robert H. Doremus, eds. Ceramic and Glass Materials: Structure, Properties, and Processing. New York: Springer, 2008.

Shelby, James E. Introduction to Glass Science and Technology. 2d ed. Cambridge, England: Royal Society of Chemistry, 2005.

Sinton, Christopher W. Raw Materials for Industrial Glass and Ceramics: Sources, Processes, and Quality Control. Hoboken, N.J.: Wiley, 2006.

Zerwick, Chloe. A Short History of Glass. Redesigned and updated 2d ed. New York: H. N. Abrams in association with the Corning Museum of Glass, 1990.

Corning Museum of Glass

A Resource on Glass.