Corning trademarked the name Pyrex for the heat-resistant borosilicate glass it had developed previously and began marketing the material for bakeware and laboratory applications.
The first use of Corning’s heat-resistant glass for cooking occurred in 1913. Various stories abound regarding this event. According to one version, Jesse T. Littleton’s wife broke a casserole in which she was about to bake a pudding, so she substituted the only vessel available, the cut-off bottom of a battery jar made of heat-resistant glass. The result was “so surprisingly good” that Corning Glass Works immediately instituted trials, furnishing the wives of laboratory technicians with glass dishes to be used in all kinds of baking. Following these successful experiments, the marketing of Pyrex bakeware began in 1915. The actual event was somewhat less serendipitous and more systematic. To place it in perspective, it is necessary to review the history of Corning Glass Works to see why the company produced a heat-resistant glass with no apparent plans to use it in the kitchen or the laboratory.
By the beginning of the twentieth century, Corning had a reputation as a company that cooperated with the world of science to improve existing products and develop new ones. In the 1870’s, Corning had hired university scientists to advise on improving the optical quality of glasses, an early example of today’s common practice of academics consulting for industry. The company had worked with Thomas Alva Edison
Lenses for oil or gas lanterns were vulnerable to weather damage; that is, they could shatter if they were sprayed with cold rain or wet snow after being heated by the flame that produces the light. When a lens in a red “stop” light broke, the lantern appeared to be giving a clear “proceed” signal; this problem caused many accidents and near misses in railroading in the late nineteenth century. When Eugene C. Sullivan established Corning’s research laboratory in 1908 (the first of its kind devoted to glass research), the task that he undertook with his assistant William C. Taylor was that of making a heat-resistant glass for railroad lantern lenses.
The problem was that ordinary flint glass (the kind in bottles and windows, made by melting together silica sand, soda, and lime) has a fairly high thermal expansion but a poor heat conductivity. This means that when it is heated, the outer parts can expand greatly, long before the inner parts are heated at all; conversely, when it is cooled, the outer parts can contract before the inner parts cool. Either situation can cause the glass to break, sometimes violently.
Two solutions were possible: improvement of the thermal conductivity and reduction of the thermal expansion. The first is what metals do; most metals have an expansion with heat much greater than that of glass, but they conduct heat so quickly that they expand nearly equally throughout and seldom lose structural integrity from uneven expansion. Glass, however, is inherently a poor heat conductor, so this approach was not possible. Sullivan and Taylor had to find a formulation that had little or no thermal expansivity. Pure silica (one example is quartz) fits this description, but it is expensive and, with its high melting point, very difficult to work. The formulation that Sullivan and Taylor devised was a borosilicate glass, essentially a soda-lime glass with the lime replaced by borax, with a small amount of alumina added. This gave the low thermal expansion needed for signal lenses. It also turned out to have good acid resistance, which led to its being used for the battery jars required for railway telegraph systems and other applications. Corning marketed this glass as Nonex (for “nonexpansion glass”).
Littleton joined Corning’s research laboratory in 1913. The company had a very successful lens and battery jar material, but no one had even considered it for cooking or other heat-transfer applications, because prevailing opinion was that glass absorbs and conducts heat poorly. This meant that in glass pans, cake batters, pies, and other baked foods would cook on the top, where they were exposed to hot air, but would remain cold and wet (or at least undercooked) next to the glass surfaces. Further, stove burner operations were out of the question. As a physicist, Littleton knew that glass absorbs radiant energy very well. This solved the heat-conduction problem by giving a source of heat in the glass vessel. It would also give glass a significant advantage over metal in baking. Metal bakeware mostly reflects radiant energy to the walls of the oven, where it is lost ultimately to the surroundings. Glass would absorb this radiant energy and conduct it evenly to the vessel’s contents, giving a better result than that of the metal bakeware. Moreover, glass would not absorb and carry over flavors from one baking to the next, as some metals do.
Littleton took a cut-off battery jar made of Nonex home with him and asked his wife to bake a cake in it. He then took the cake to the laboratory the next day and handed pieces around, not disclosing the method of baking until all had agreed that the results were excellent. With this agreement, he was able to commit laboratory time to developing variations on the Nonex formula that were more suitable for cooking. The result was Pyrex, patented and trademarked in May, 1915. Although the patents have long since expired, the trademark remains the property of Corning. The etymology of the name is interesting. The association with the Greek root pyr (fire) is only fortuitous; the original intent was to model the name on the existing Nonex, but with the word “pie” substituted before the suffix, as the first piece explicitly fabricated as a baking dish was a pie plate.
Initial sale of Pyrex bakeware took place at the Jordan Marsh department store in Boston in 1915. In addition to the pie plate, the company offered cake pans, custard cups, and bread pans. Within a short time, Americans overcame their skepticism about glass as a cooking material, and in 1919 more than 4.5 million pieces of Pyrex bakeware were sold. In the 1930’s, Corning introduced Pyrex Flameware, with a new glass formulation that could withstand the extreme heat of stove-top cooking. The cookery revolution was complete.
In the same year Corning began marketing Pyrex for cooking, the company also introduced Pyrex laboratory glassware. At the beginning of the twentieth century, the glassware used in American laboratories came from Germany. After World War I cut off the supply, Corning filled the gap with Pyrex beakers, flasks, and other items, and, by the end of the war, the Pyrex products were so well entrenched that they remained. Today, Corning-style glassware is found in laboratories all over the world.
Corning’s introduction of Pyrex cookware brought a wide range of products, in an entirely new material, to American kitchens and, within a very few years, to kitchens around the world. In the years after Flameware was introduced, Corning went on to produce a variety of other products and materials, such as tableware in tempered opal glass; cookware made of Pyroceram, a glass product made crystalline by heat treatment with such mechanical strength as to be virtually unbreakable; and even hot plates and stoves topped with Pyroceram. It became possible to outfit a kitchen and dining room exclusively with heat-resistant glasses or glass-ceramics, although most households continued to mix these with dishes and cookware in metals and conventional ceramics. The revolution that Corning brought to the kitchen was a revolution by way of addition to existing materials and methods.
In the laboratory, in contrast, the revolution was one of total replacement. The delicate blown-glass equipment from Germany that had previously been the standard was completely displaced by the more rugged and heat-resistant machine-made Pyrex ware. Any number of operations are possible with Pyrex that cannot be performed safely using vessels made of flint glass: Test tubes can be thrust directly into burner flames, with no preliminary warming; beakers and flasks can be heated on hot plates, unlike flint glass, which (because contact and heat transfer occur at only a few points) almost inevitably shatters when heated this way; materials that dissolve with evolution of heat, such as sodium or potassium hydroxide, can be made into solutions directly in Pyrex storage bottles, a process that would leave the benchtop and the floor covered with hot caustic solution if carried out in regular glass; thermometers can be placed directly into heating baths 300 degrees or more above room temperature.
The list of heating and cooling operations that can be done in Pyrex or other borosilicate vessels (for example, Kimble’s Kimax) and cannot be done in regular glass can be expanded almost indefinitely. It is safe to say that in any laboratory doing “wet chemistry” (that is, syntheses and analyses in solution in water or other solvents), if all glassware were replaced overnight with that used before Pyrex was developed, work would immediately stop. Weeks would go by while chemists and technicians retrained themselves in different techniques and slowly reached their previous level of activity. Pyrex revolutionized laboratory practices.
Other unique applications found for Pyrex since its introduction in 1915 include as the material of choice for lenses in the great reflector telescopes, beginning in 1934 with that at the Palomar Observatory in California. By its nature, astronomical observation must be done with the scope open to the weather. This means that the mirror must not change shape with temperature variations, which rules out metal mirrors. Silvered (or aluminized) Pyrex serves very well, and Corning developed great expertise in casting and machining Pyrex blanks for mirrors of all sizes. Pyrex also was found to be useful as the glass of glass fibers, whether for insulation or as a component in glass-plastic construction materials. Pyrex is less brittle than regular glass and has less of a tendency to break into tiny, needlelike shards.
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Hecht, Jeff. City of Light: The Story of Fiber Optics. New York: Oxford University Press, 1999. Presents the history of the development of fiber optics, in which Corning’s innovations in glass products played an important role. Covers developments in the manufacture of glass since Victorian times that led up to fiber-optic technology. -
Hollister, George B. “The Battery Jar That Built a Business.” Gaffer, July, 1946, 3-6, 18. An account of the original development of Pyrex bakeware, followed by much information on manufacturing and marketing practice. Gaffer is an in-house publication of the Corning Glass Works. -
_______. Historical Highlights, Corning. Corning, N.Y.: Corporate Communications Division, Corning Glass Works, 1982. Pamphlet provides a useful chronology of major events in the company’s history from 1851 to 1981. Lists both technical and managerial advances. -
_______. “Pyrex Brand Glass Found Suitable for Oven Cooking: 1913.” In Historical Records of Corning Glass Works 1851-1930. Corning, N.Y.: Corning Glass Works, Archives and Records Division, 1931. Typescript from the Archives and Records Division of Corning Glass provides good technical historical background. -
_______. “The Story of Pyrex and Heat Resistant Glass.” Leader, October 21, 1968, B6. Newspaper account from the local paper in Corning, New York. Article is authoritative if brief, with some information not easily found elsewhere. -
Morey, George W. The Properties of Glass. New York: Reinhold, 1938. Gives technical material, in tabular and discussion form, of types of glass, including Pyrex. Discusses formulations and chemical, physical, and engineering properties of different kinds of glass. -
Uhlmann, Donald R. Glass: Science and Technology. 4 vols. San Diego, Calif.: Academic Press, 1979-1990. Standard work presents discussion of glass formulas.
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