Borosilicate glass

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Borosilicate glass is a particular type of glass, better known under the brand names Pyrex, Kimax, and Endural. It was first developed by German glassmaker Otto Schott in the late 19th century and sold under the brand name "Duran" in 1893. After Corning Glass Works introduced Pyrex in 1915, it became a synonym for borosilicate glass in the English-speaking world. Holophane manufactures original equipment lenses for street lights under the Endural brand name. Bomex is a brand of borosilicate glassware made in China for VEE GEE Scientific, Inc.

In addition to the quartz, sodium carbonate, and calcium carbonate traditionally used in glassmaking, boron is used in the manufacture of borosilicate glass. Typically, the resulting glass composition is about 70% silica, 10% boric oxide, 8% sodium oxide, 8% potassium oxide, and 1% calcium oxide. Though somewhat more difficult to make than traditional glass (Corning conducted a major revamp of their operations to make it), it is economical to produce because its superior durability, chemical and heat resistance finds excellent use in chemical laboratory equipment, cookware, lighting, and in certain cases, windows.

Borosilicate glass has a very low thermal expansion coefficient, making it a popular material for objects like telescope mirrors, where it is essential to have very little deviation in shape. It is also used in the processing of high-level nuclear waste, where the waste is immobilised in the glass through a process known as vitrification (contrast with Synroc).

Optically, borosilicate glasses are crown glasses with low dispersion (Abbe numbers around 65) and relatively low refractive indices (1.51 - 1.54 across the visible range).

Unexpectedly, use for Pyrex grew outside of scientific and industrial circles. New lampworking techniques led to artistic uses. Often the art can be refined and then rapidly-produced turning it into novelties that quickly degenerated into kitsch. There is a large market for cheaply reproduced trinkets, smoking pipes, bongs and other novelties. Borosilicate glass is sometimes used for high-quality beverage glassware; Bodum, Inc. markets a line of French coffee presses and double-walled beverage glasses made of borosilicate, lending them increased durability and microwave/dishwasher compatibility.

Further development in glassmaking continues to create new glass-ceramics that outperform borosilicate glass in various ways.