Pyrex

Pyrex (trademarked as PYREX and pyrex) is a type of borosilicate glass developed by Corning Incorporated in 1908. Pyrex was first introduced to the public in 1915, as a brand of clear, low-thermal-expansion glassware products, whose resistance to chemicals, electricity, and heat made it ideal for laboratory glassware and kitchenware.[1][2] In the 1930s, Corning expanded the brand to include kitchen products made of soda–lime glass and other materials.

In 1998, Corning Incorporated spun off its kitchenware division, including Pyrex cookware. Currently, Pyrex dishes are manufactured by Corelle Brands in the United States and International Cookware in Europe. Corning Incorporated continues to manufacture Pyrex scientific glassware.[3]

History

Corning Glass Works

Borosilicate glass was first made by German chemist and glass technologist Otto Schott, founder of Schott AG in 1893.

In 1908, Eugene Sullivan, director of research at Corning 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 in Leipzig, Germany.[4]

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 the lead from Nonex and developed it as a consumer product.[4] Pyrex made its public debut in 1915 during World War I and was positioned as an American-made alternative to Duran.

Trademark

Pyrex remains a trademark of Corning Incorporated, but is licensed by two dinnerware manufacturers.[28][29]

Corning Incorporated continues to manufacture PYREX (all uppercase) laboratory glassware for international markets.[28] The pyrex (all lowercase, introduced in 1975[30]) trademark is now used for kitchenware sold in the United States, South America, Asia, and Australia.[29] In Europe, Africa, and the Middle East, a variation of the PYREX (all uppercase) trademark is licensed by International Cookware.[29]

Composition

Older clear-glass Pyrex manufactured by Corning, International Cookware's Pyrex products, and Pyrex laboratory glassware are made of borosilicate glass. According to the National 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.[32]

According to glass supplier Pulles and Hannique, borosilicate Pyrex is made of Corning 7740 glass and is equivalent in formulation to Schott Glass 8330 glass sold under the "Duran" brand name.[33] 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.

Starting around the 1950s, Corning began making Pyrex out of thermally tempered soda–lime glass, instead of borosilicate glass, due to lower manufacturing costs.[34] Some plants moved to tempered soda–lime formulations, while others continued to produce borosilicate Pyrex.[35]

Patterns and collecting

Pyrex has achieved somewhat of a cult following[64] through its various colours and patterns produced after World War II,[65] lending itself to collectors.[64][66] Some valuable patterns include the 1956 Pink Daisy or the 1983 Colonial Mist.[66] Depending on condition, prices can range from $100 for single pieces to $500 for a collection, according to flea market expert Nicolas Martin.[66] Some pieces have sold for several thousand dollars on eBay.[67]

Use in telescopes

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 approached Corning with the challenge of fabricating the 200 in telescope mirror for the California Institute of Technology's Palomar Observatory project.[68] A previous effort to fabricate the optic from fused quartz had failed, with the cast blank having voids. The mirror was cast by Corning during 1934–1936 out of borosilicate glass.[69] 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 the Corning Museum of Glass.[70]

Gallery

General and cited references

External links

Pyrex Love, a vintage Pyrex reference site

References

Nina Friend. A Brief History of Pyrex Food & Wine, 26 January 2026, retrieved 27 February 2026^
Regan Brumagen. The Beginning of Pyrex Corning Museum of Glass, retrieved 27 February 2026^
Laboratory Glassware corning.com, Corning Incorporated, retrieved 10 March 2026

Distinguishing soda–lime and borosilicate Pyrex

It is a common misconception that the logo style alone indicates the type of glass used to manufacture the bakeware.[45] In reality, Corning's introduction of soda–lime based Pyrex in the 1940s predates the introduction of the all lowercase logo by around 30 years, which first appeared in 1975.[30][43] Additionally, the transition to soda–lime was not uniform, as some plants continued to produce borosilicate pieces for a period of time, though was generally phased out by 1998.[35] This means any Pyrex manufactured in the U.S. from the 1940s to 1998 could be either borosilicate or soda–lime, regardless of the capitalization of the logo. The Corning Museum of Glass website summarizes: "The short answer is that the change from upper to lower case signified a re-branding of the trademark Pyrex® in the late 1970s but is not a conclusive way to determine, historically, what type of glass formulation the product is made from."[35]

Visual differences

When asked about any visual differences, Corning designer Herb Dann noted in a 2014 interview: "Actually, the tempered [soda-lime] is a little bluer glass, it can alter the color of it. In fact, at one time we actually had a straw color in all of the Pyrex line. Today when you walk into the company store, it's all blue and that's a cheaper glassmelt because they're not purifying, they're not taking the cobalt out. So it's a cheaper melt, but it's all tempered lime."[46] The U.S. Pyrex website notes: "You may notice that some of our Pyrex® brand glassware has a slight tint of green or blue hue to the dish. It is not a coating or added color. It comes from the raw materials in the glass itself. The blue comes from adding cobalt to the raw materials. This does not affect the performance of the dish; it is purely cosmetic."[47]

U.S. post–1998

From 1998, World Kitchen (Later Corelle Brands, then Anchor Hocking) used the Corning soda–lime formulation at their plant in Charleroi, Pennsylvania.[43] The plant was shut down in April 2025, after 132 years of operation.[48] Production was then shifted to Lancaster, Ohio by new owners Anchor Hocking.[49] Ultimately, production of all U.S. Pyrex since 1998 has been made of soda–lime glass with the lowercase logo.[50]

England

In 1921, James A Jobling acquired the licence to produce Pyrex in the UK. The original kiln was replaced with a borosilicate furnace to create the Pyrex.[51] Production started in 1922 at his Sunderland factory in England, and continued for over 50 years. In 1973, the licence expired, and Corning took control of the factory and the Jobling company.[52][53][54] Pyrex produced before Corning took over was stamped with a "JAJ" symbol.[55] Production at the facility took place until 2007 when it was shut down, and production of Pyrex was shifted to France.[56] All Pyrex made at the factory was borosilicate.[51]

France

Production in France began in 1922 with the glassblowers Clovis and Léon Régent at the Bagneaux-sur-Loing glassworks. Production continued for several years until the factory was relocated to Châteauroux in 1970 where it continues as of 2026.[57] All Pyrex made at the factory is borosilicate with the uppercase logo.[29][50]

Australia

Australian Pyrex is distributed by Corelle Brands, who offer the lowercase soda–lime glass.[58][59] However, they also offer the French-made borosilicate glass.[58][60] Additionally, borosilicate glass with the lowercase logo is offered in the "Bake N Serve" and "Cook N Serve" ranges which are produced in China.[50][61][62]

Previously, Pyrex was produced in Australia by Crown Crystal Glass from 1926.[63]

History

Corning Glass Works

Trademark

Composition

Patterns and collecting

Use in telescopes

Gallery

See also

General and cited references

External links

References

Corelle Brands

European history

Distinguishing soda–lime and borosilicate Pyrex

Visual differences

U.S. post–1998

England

France

Australia

Visual differences

U.S. post–1998

England

France

Australia