Pyrex is a brand name of borosilicate glass introduced by Corning Glass Works in 1924. Though borosilicates had been produced before, the name Pyrex is widely used as a synonym for the material.
Pyrex is created by adding boron to the traditional glassmaker's "frit" of silicate sand, soda, and ground lime. The boron gave this new borosilicate glass a reduced thermal coefficient (about one-third that of ordinary glass), making it more resistant to heat. Pyrex is also lighter in weight. Since Pyrex melts at a higher temperature than ordinary glass, some new techniques were required to bring Pyrex into industrial production. Borrowing from the welding trade, new burners combining oxygen with natural gas were required.
Caltech's famous 200-inch telescope mirror at Mount Palomar was cast by Corning during 1934-36 out of Pyrex, which expands and contracts less than ordinary glass.
Unexpectedly, Pyrex and the new "lampworking" techniques generated a cottage industry in quickly-produced glass novelties that quickly degenerated into kitsch.
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Reference
- Rogove, Susan Tobier; Steinhauer, Marcia Buan (1993). Pyrex by Corning: A Collector's Guide. Antique Publications. ISBN 091541094X