Tuesday, November 20, 2012

A lead-free borosilicate glass, G 702 EJ, named Py-Right, Pie Rite and eventually Pyrex

PYREX® is  is a transparent, lead-free borosilicate glass with a low thermal expansion coefficient—an example of  a material with good heat shock resistance. The excellent thermal properties of Pyrex facilitate its use at high operating temperatures [1].

Pyrex-branded borosilicate glass products were invented and produced at Corning Glass Works in the upstate New York city of Corning, nicknamed Crystal City for its legacy of glass factories and glass cutting shops. In the early 20th century, a hot flame tolerant borosilicate glass, named “fire glass”or  Nonex, was successfully manufactured by the Corning specialty glassmaker and integrated as components in electric lightbulbs and railway signal lamps [2-5]. A borosilicate glass is made by adding borax (sodium tetraborate decahydrate) to the typical glass composition of silica, sodium oxide and lime. By further employing other minor additives, glass properties can be fine-tuned for desired applications.

Pyrex was developed by Corning scientist William Churchill, based on Corning's Nonex know-how. While Nonex released lead when exposed to acids (for example from food), a lead-free borosilicate variation with code G 702 EJ, did not. The latter showed promising properties for being used as ovenware and laboratory glassware.

In 1915, Churchill and Corning made G 702 EJ public under the tradename Pyrex—rhyming with Nonex—after playing with names such as Py-Right and Pie Rite, referring to the first appetizingly prepared cakes and custards in Pyrex dishes. In 1916, these look-right-through dishes were marketed and advertized as ovenware that saves time, labor and fuel [5]: one of the earliest ads further states that Pyrex will not crack, chip nor craze, not be affected by the hottest oven and that “Pyrex is everlastingly sanitary, durable, easy to wash, a constant source of satisfaction in the well-appointed home.”

Keywords: history, materials science, glass research, glass engineering, borosilicates, labware, kitchenware, baking, cooking.

References and more to explore
[1] Pyrex® Borosilicate Glass [www.pgo-online.com/intl/katalog/pyrex.html].
[2] Washington Glass School: Historical Glass Fun Facts: Invention of Pyrex & the Studio Glass Movement [washingtonglass.blogspot.com/2012/01/historical-glass-fun-facts-invention-of.html].
[3] History of Pyrex® [www.classickitchensandmore.com/page_4.html].
[4] William S. Ellis: Glass. Avon Books, Inc., New York, 1998; pp. 49-50.
[5] Regina Lee Blaszczyk: Cooking with Glass. Chemical Heritage Fall 2012/Winter 2013, 30 (3), pp. 8-9 [www.chemheritage.org/discover/online-resources/thanks-to-chemistry/ttc-food-pyrex.aspx].


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