Pyrex was 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 Pyex into industrial production. Borrowing from the welding trade, new burners combining oxygen with natural gas were required.
Collecting the utilitarian kitchen glass made by Corning of Pyrex is a hobby that has spawned its own book, Pyrex By Corning: A Collector's Guide.
Caltech's famous 200-inch telescope lens 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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