Pyrex (trademarked as PYREX) is a brand introduced by
Corning Inc. in
1908 for a line of clear, low-thermal-expansion borosilicate glass
used for laboratory glassware and kitchenware. It was later expanded
to include clear and opal ware products made of soda-lime glass.
Corning no longer manufactures or markets consumer glass kitchenware
Corelle Brands, which was spun off from
Corning Inc. in
1998 under the name Corning Consumer Products Company and since
renamed, continues to license the pyrex (all lower case) brand for
their tempered soda-lime glass line of kitchenware products sold for
the consumer market in the United States, South America, and Asia. In
the regions of Europe, Africa, and the
Middle East the PYREX (all
upper case) brand is licensed by International Cookware for use on
their borosilicate glass products. The brand name has also been used
for non-glass kitchen utensils and cookware in various regions for
3 Use in telescopes
5 External links
PYREX glassware from Corning Inc.
Newspaper ad showing
Pyrex bakeware from 1922
Borosilicate glass was first made by German chemist and glass
technologist Otto Schott, founder of
Schott AG in 1893, 22 years
before Corning produced the
Schott AG sold the product
under the name "Duran".
In 1908, Eugene Sullivan, director of research at Corning
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. 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. Pyrex
made its public debut in 1915 during World War I, positioned as an
American-produced alternative to Duran.
A Corning executive gave the following account of the etymology of the
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
the Greek pyr and the
Latin rex we have always taken the position that
no graduate of Harvard would be guilty of such a classical hybrid.
Actually, we had a number of prior trade-marks ending in the letters
ex. One of the first commercial products to be sold under the new mark
was a pie plate and in the interests of euphonism the letter r was
inserted between pie and ex and the whole thing condensed to PYREX.
In the late 1930s and 1940s, Corning also introduced other products
Pyrex brand, including opaque tempered soda-lime glass for
bowls and bakeware, and a line of
Pyrex Flameware for stovetop use;
this borosilicate glass had a bluish tint caused by the addition of
alumino-sulfate. In 1958 an internal design department was
started by John B. Ward. He redesigned the
Pyrex ovenware and
Flameware. Over the years, designers such as Penny Sparke, Betty
Baugh, Smart Design, TEAMS Design, and others have contributed to the
design of the line.
Corning divested itself of the Corning Consumer Products Company (now
Corelle Brands) in 1998 and production of consumer Pyrex
products went with it. Its previous licensing of the name to Newell
Europe remained in effect. France-based cookware maker Arc
International acquired Newell's European business in early 2006 and
currently owns rights to the brand in Europe, the
Middle East and
A clear borosilicate glass
Pyrex measuring cup produced by Corning
(right) and a clear tempered
Pyrex soda-lime glass measuring cup
World Kitchen (left, differentiated by its different logo
and bluish tint)
Pyrex manufactured by Corning, Arc International's
Pyrex products, and
Pyrex laboratory glassware is made of borosilicate
glass. According to the National Institute of Standards and
Pyrex is composed of (as percentage of
weight): 4.0% boron, 54.0% oxygen, 2.8% sodium, 1.1% aluminum, 37.7%
silicon, and 0.3% potassium.
According to glass supplier Pulles and Hannique, borosilicate
made of Corning 7740 glass and is equivalent in formulation to Schott
Glass 8330 glass sold under the "Duran" brand name. 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,
Beginning in the 1980s, production of
Pyrex glass cookware
manufactured by Corning (and later
Corelle Brands, after the consumer
division was spun off and renamed) was shifted to tempered soda-lime
glass, like their opal bakeware. 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. Also, it is cheaper to produce and more
environmentally friendly. However, its thermal shock resistance is
lower than borosilicate's, leading to potential breakage from heat
stress if used contrary to recommendations. European
Pyrex is still
made from borosilicate.
The differences between Pyrex-branded glass products has also led to
urban legends and the concern of safety issues—in 2008, the 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 magazine Consumer
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. However,
they admitted their testing conditions were “contrary to
instructions” provided by the manufacturer. 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
Use in telescopes
Because of its low expansion characteristics,
Pyrex borosilicate glass
is often the material of choice for reflective optics in astronomy
George Ellery Hale
George Ellery Hale approached Corning with the challenge of
fabricating the 200-inch (5.1 m) telescope mirror for the
California Institute of Technology's
Palomar Observatory project.
A previous effort to fabricate the optic from fused quartz had failed,
the cast blank having voids. The mirror was cast by Corning during
1934–1936 out of borosilicate glass. 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.
Pyrex Bakeware, Carroll M. Gantz, Design Chronicles:
Significant Mass-produced Designs of the 20th Century, Schiffer
Publications, Ltd. 2005
^ Mathews, MM (1957). "title unknown". American Speech. 32 (4):
^ "PYREX Flameware". The Antique Attic. Archived from the original on
January 4, 2011. Retrieved 5 June 2015.
^ a b "Exploding Pyrex, Urban Legend reference". Snopes.com. Retrieved
^ a b "Manufacturing History".
Pyrex Products. Archived from the
original on 2 October 2011. Retrieved 5 June 2015.
Arc International page". Hoover's. Archived from the original on 29
September 2007. Retrieved 5 June 2015.
^ Hibberd, Susan (2007). The Little Book of Collectable British Pyrex.
Exposure Publishing. ISBN 1-84685-556-X.
Glass Ovenware". Arc International. 2005. Archived from the
original on 2008-03-11. Retrieved 2008-03-17.
^ "Composition of
Pyrex Glass". National Institute of Standards and
Technology. Retrieved September 8, 2016.
Pyrex is Made". MadeHow.com. n.d.
^ "Borosilicate glass". Archived from the original on 15 March 2012.
Retrieved 5 June 2015.
^ Aikins, Jim. "Setting the Record Straight: The Truth About PYREX".
Pyrex Products. Archived from the original on 26 October 2011.
Retrieved 5 June 2015.
^ a b Butterworth, Trevor (14 October 2009). "Exploding the exploding
Pyrex rumor". STATS. Statistical Assessment Service. Archived from the
original on 20 November 2014. Retrieved 5 June 2015.
Consumer Reports Breaks A Lot Of
Glass Investigating Shattering
Pyrex Bakeware, The Consumerist
^ "FOIA requests examine glass bakeware that shatters". Consumer
Reports. Retrieved 7 February 2012.
Glass Giant". Corning Museum of Glass. Corning Museum of Glass.
Retrieved 30 January 2015.
^ "A History of Palomar Observatory". Palomar Observatory. California
Institute of Technology. 28 May 2015. Retrieved 5 June 2015.
^ "200-inch Disk". Corning Museum of Glass. Corning Museum of Glass.
Retrieved 30 January 2015.
DeGuire, Ellen (September 11, 2012). "New paper addresses causes of
shattering glass cookware; margin of safety described as
'borderline'". American Ceramic Society. Retrieved 2012-09-17. 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
Gantz, Carroll, (2001). DESIGN CHRONICLES: Significant Mass-produced
Products of the 20th Century, Schiffer Publishing,
Rogove, Susan Tobier; Steinhauer, Marcia B. (1993).
Pyrex by Corning:
A Collector's Guide. Antique Publications. ISBN 0-915410-94-X.
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