Pyrex (trademarked asPYREX andpyrex) is abrand of glassware byCorning Inc. best known for the rectangular roasters with which its name has become nearly synonymous. Pyrex was first introduced in 1915 as a line of clear, low-thermal-expansionborosilicate glass whose resistance to chemicals, electricity, and heat made it ideal forlaboratory glassware andkitchenware. In the 1930s Corning Inc expanded the brand to include kitchen products made ofsoda–lime glass and other materials.[1]
In 1998, the kitchenware division of Corning Inc. responsible for the development of Pyrex spun off from its parent company as Corning Consumer Products Company, subsequently renamedCorelle Brands. Corning Inc. no longer manufactures or markets consumer products, only industrial ones.
Borosilicate glass was first made by German chemist and glass technologistOtto Schott, founder ofSchott AG in 1893, 22 years before Corning produced the Pyrex brand. Schott AG sells the product under the name "Duran".
In 1908, Eugene Sullivan, director of research atCorning Glass Works, developed Nonex, a borosilicate low-expansion glass, to reduce breakage in shock-resistant lantern globes and battery jars. Sullivan had learned about Schott's borosilicate glass as a doctoral student inLeipzig,Germany. Jesse Littleton of Corning discovered the cooking potential of borosilicate glass by giving his wife Bessie Littleton a casserole dish made from a cut-down Nonex battery jar. Corning removed thelead from Nonex and developed it as a consumer product.[2] Pyrex made its public debut in 1915 duringWorld War I, positioned as an American-produced alternative to Duran.
A Corning executive gave the following account of theetymology of the name "Pyrex":
The word PYREX is probably a purely arbitrary word which was devised in 1915 as a trade-mark for products manufactured and sold by Corning Glass Works. While some people have thought that it was made up from theGreekpyr and theLatinrex, we have always taken the position that no graduate ofHarvard would be guilty of such a classicalhybrid. Actually, we had a number of prior trade-marks ending in the lettersex. One of the first commercial products to be sold under the new mark was a pie plate, and in the interests ofeuphonism the letter r was inserted betweenpie andex and the whole thing condensed to PYREX.[3]
Corning purchased theMacbeth-Evans Glass Company in 1936 and their Charleroi, PA plant was used to produce Pyrex opal ware bowls and bakeware made of tempered soda–lime glass.[4] In 1958 an internal design department was started by John B. Ward. He redesigned the Pyrex ovenware and Flameware. Over the years, designers such asPenny Sparke,Betty Baugh, Smart Design, TEAMS Design, and others have contributed to the design of the line.
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Corning divested itself of the Corning Consumer Products Company (now known asCorelle Brands) in 1998 and production of consumer Pyrex products went with it. Its previous licensing of the name toNewell Cookware Europe remained in effect.[5]
France-based cookware makerArc International acquired Newell's European business in early 2006[6] to own rights to the brand inEurope, theMiddle East andAfrica.[7][8] In 2007, Arc closed the Pyrex soda–lime factory inSunderland, UK moving all European production to France. The Sunderland factory had first started making Pyrex in 1922.[9]
In 2014,Arc International sold off its Arc International Cookware division which operated the Pyrex business to Aurora Capital for its Resurgence Fund II. The division was renamed the International Cookware group.[10] London-basedprivate equity firm Kartesia[11] purchased International Cookware in 2020.[12]
In 2021, Pyrex rivalDuralex was acquired by International Cookware group for €3.5 million (US$4.2m).[13][14][15]
In March 2019, Corelle Brands, the makers of Pyrex in the United States, merged with Instant Brands, the makers of theInstant Pot.[16] On June 12, 2023, Instant Brands filed forChapter 11 bankruptcy after high interest rates and waning access to credit hit its cash position and made its debts unsustainable.[17] The company emerged from bankruptcy on February 27, 2024 under the previous Corelle Brands moniker, after having sold off its appliance business ("Instant" branded products).[18][19]
InEurope,Africa, and theMiddle East, a variation of thePYREX (all uppercase) trademark is licensed byInternational Cookware[20] for bakeware that has been made of numerous materials including borosilicate and soda–lime glass, stoneware, metal, plus vitroceramic cookware.[21] Thepyrex (all lowercase, introduced in 1975[22]) trademark is now used for kitchenware sold in theUnited States,South America, andAsia.[23] In the past, the brand name has also been used for kitchen utensils and bakeware by other companies in regions such as Japan and Australia.
It is a common misconception that the logo style alone indicates the type of glass used to manufacture the bakeware.[24] Additionally, Corning's introduction of soda-lime-glass-based Pyrex in the 1940s predates the introduction of the all lowercase logo by nearly 30 years.[25][22][26] Nevertheless, all "pyrex" manufactured since 1998 in the United States is soda-lime glass,[27] while all French-made "PYREX" glassware is borosilicate.[28]
Older clear-glass Pyrex manufactured by Corning, Arc International's Pyrex products, and Pyrexlaboratory glassware are made of borosilicate glass. According to theNational Institute of Standards and Technology, borosilicate Pyrex is composed of (as percentage of weight): 4.0%boron, 54.0%oxygen, 2.8%sodium, 1.1%aluminium, 37.7%silicon, and 0.3%potassium.[29][30]
According to glass supplier Pulles and Hannique, borosilicate Pyrex is made of Corning 7740 glass and is equivalent in formulation toSchott Glass 8330 glass sold under the "Duran" brand name.[31] The composition of both Corning 7740 and Schott 8330 is given as 80.6%SiO2, 12.6%B2O3, 4.2%Na2O, 2.2%Al2O3, 0.1%CaO, 0.1%Cl, 0.05%MgO, and 0.04%Fe2O3.
In the late 1930s and 1940s, Corning also introduced new product lines under the Pyrex brand using different types of glass. Opaquetemperedsoda–lime glass was used to create decorated opal ware bowls and bakeware, and aluminosilicate glass was used for Pyrex Flameware stovetop cookware. The latter product had a bluish tint caused by the addition of alumino-sulfate.[32][33]
Beginning in the 1980s, production of clear Pyrex glass products manufactured in the USA by Corning was also shifted to tempered soda–lime glass, like their popular opal bakeware.[25] This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate—making it more resistant to physical damage when dropped, which is believed to be the most common cause of breakage in glass bakeware. The glass is also cheaper to produce and more environmentally friendly. Its thermal shock resistance is lower than borosilicate's, leading to potential breakage from heat stress if used contrary to recommendations. Since the closure of the soda–lime plant in England in 2007, European Pyrex has been made solely from borosilicate.[5][34][35]
The differences between Pyrex-branded glass products has also led to controversy regarding safety issues—in 2008, theU.S. Consumer Product Safety Commission reported it had received 66 complaints by users reporting that their Pyrex glassware had shattered over the prior ten years yet concluded that Pyrex glass bakeware does not present a safety concern. The consumer affairs magazineConsumer Reports investigated the issue and released test results, in January 2011, confirming that borosilicate glass bakeware was less susceptible to thermal shock breakage than tempered soda lime bakeware.[36] They admitted their testing conditions were "contrary to instructions" provided by the manufacturer.[33][37] STATS analyzed the data available and found that the most common way that users were injured by glassware was via mechanical breakage, being hit or dropped, and that "the change to soda lime represents a greater net safety benefit."[34]
Because of its low expansion characteristics, borosilicate glass is often the material of choice for reflective optics in astronomy applications.
In 1932,George Ellery Hale approachedCorning with the challenge of fabricating the 200-inch (5.1 m) telescope mirror for theCalifornia Institute of Technology'sPalomar Observatory project.[38] A previous effort to fabricate the optic fromfused quartz had failed, with the cast blank having voids. The mirror was cast by Corning during 1934–1936 out of borosilicate glass.[39] After a year of cooling, during which it was almost lost to a flood, the blank was completed in 1935. The first blank now resides in theCorning Museum of Glass.[40]
Their investigation confirmed the borosilicate glass would withstand a much larger rapid temperature change. According to their calculation and those of others, soda lime glass cookware shatters more frequently because, in theory, it can only resist fracture stress for temperature differentials less than about 55 °C (99 °F). In contrast, they estimate that the borosilicate glassware could tolerate a temperature differential of about 183 °C (330 °F), a three-fold difference.
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