Editing Pyrex (section)

== Composition ==
[[File:Pyrex and PYREX.jpg|thumb|right|alt=Two clear measuring jugs featuring red text. The jug on the right is wider than the jug on the left.| A clear tempered ''pyrex'' soda–lime glass measuring cup produced by Instant Brands (left, differentiated by its different logo and bluish tint), and a clear borosilicate glass ''PYREX'' measuring cup produced by Corning (right)]]

Older clear-glass Pyrex manufactured by Corning, Arc International'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]].<ref>{{cite web | publisher = [[National Institute of Standards and Technology]]  | title = Composition of Pyrex Glass |access-date = September 8, 2016 | url = http://physics.nist.gov/cgi-bin/Star/compos.pl?matno=169}}</ref><ref>{{cite web | publisher = MadeHow.com | title = How Pyrex is Made | date = n.d. | url = http://www.madehow.com/Volume-7/Pyrex.html}}</ref>

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.<ref>{{cite web | url = http://www.pulleshanique.com/02_borosilicate-glass.htm | title = Borosilicate glass | access-date = 5 June 2015|archive-url=https://web.archive.org/web/20120315092729/http://www.pulleshanique.com/02_borosilicate-glass.htm|archive-date=15 March 2012}}</ref> The composition of both Corning 7740 and Schott 8330 is given as 80.6% {{chem2|SiO2|link=silicon dioxide}}, 12.6% {{chem2|B2O3|link=boron trioxide}}, 4.2% {{chem2|Na2O|link=sodium oxide}}, 2.2% {{chem2|Al2O3|link=aluminium oxide}}, 0.1% {{chem2|CaO|link=calcium oxide}}, 0.1% {{chem2|Cl|link=chlorine}}, 0.05% {{chem2|MgO|link=magnesium oxide}}, and 0.04% {{chem2|Fe2O3|link=iron(III) oxide}}.

In the late 1930s and 1940s, Corning also introduced new product lines under the Pyrex brand using different types of glass. Opaque [[tempered glass|tempered]] [[soda–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.<ref>{{cite web |title=PYREX Flameware |url=http://www.nettally.com/attic/Pyrexflameware.htm |archive-url=https://web.archive.org/web/20110104125655/http://www.nettally.com/attic/Pyrexflameware.htm |archive-date=January 4, 2011 |access-date=5 June 2015 |website=The Antique Attic}}</ref><ref name="Snopes">{{cite web |title=Exploding Pyrex, Urban Legend reference |date=18 September 2009 |url=http://www.snopes.com/food/warnings/pyrex.asp |access-date=2011-01-08 |publisher=[[Snopes.com]]}}</ref>

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.<ref name="Aikins">{{cite web |url=http://www.pyrexware.com/thetruthaboutpyrex/index.htm |first=Jim |last=Aikins |title=Setting the Record Straight: The Truth About PYREX |publisher=Pyrex Products |access-date=5 June 2015|archive-url=https://web.archive.org/web/20111026114654/http://www.pyrexware.com/index.asp?pageId=30|archive-date=26 October 2011}}</ref> This change was justified by stating that soda–lime glass has higher mechanical strength than borosilicate{{emdash}}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.<ref name="History" /><ref name=":0">{{cite web|last1=Butterworth|first1=Trevor|title=Exploding the exploding Pyrex rumor| url=http://stats.org/stories/2009/exploding_pyrex_oct14_09.html |website=STATS |publisher=Statistical Assessment Service |access-date=5 June 2015 |archive-url=https://web.archive.org/web/20141120095647/http://stats.org/stories/2009/exploding_pyrex_oct14_09.html|archive-date=20 November 2014 |date=14 October 2009}}</ref><ref>[http://consumerist.com/2010/12/consumer-reports-breaks-a-lot-of-glass-investigating-shattering-pyrex.html Consumer Reports Breaks A Lot Of Glass Investigating Shattering Pyrex Bakeware] {{Webarchive|url=https://web.archive.org/web/20120514061947/http://consumerist.com/2010/12/consumer-reports-breaks-a-lot-of-glass-investigating-shattering-pyrex.html |date=2012-05-14 }}, The Consumerist</ref>

The differences between Pyrex-branded glass products has also led to controversy regarding safety issues{{emdash}}in 2008, the [[U.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 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.<ref>{{Cite web|url=https://gizmodo.com/the-pyrex-glass-controversy-that-just-wont-die-1833040962|title=The Pyrex Glass Controversy That Just Won't Die|last=Estes|first=Adam Clark|date=March 16, 2019|website=Gizmodo|language=en-US|access-date=2019-03-22}}</ref> They admitted their testing conditions were "contrary to instructions" provided by the manufacturer.<ref name="Snopes" /><ref>{{cite web|title=FOIA requests examine glass bakeware that shatters|url=http://news.consumerreports.org/safety/2010/12/foia-requests-examine-glass-bakeware-that-shatters-.html?EXTKEY=I91CONL&CMP=OTC-ConsumeristLinks|publisher=[[Consumer Reports]]|access-date=7 February 2012|archive-url=https://web.archive.org/web/20111206025207/http://news.consumerreports.org/safety/2010/12/foia-requests-examine-glass-bakeware-that-shatters-.html?EXTKEY=I91CONL&CMP=OTC-ConsumeristLinks|archive-date=6 December 2011}}</ref> 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."<ref name=":0" />