Pyrex

Pyrex
Pyrex · Public domain · source
Name	Pyrex
Caption	A Corning Inc. measuring cup made from borosilicate glass.
Density	~2.23 g/cm³
Thermal expansion	3.25 × 10−6 /°C
Manufacturer	Corning Inc., World Kitchen

Pyrex. Pyrex is a brand name for a type of glassware, originally made from borosilicate glass, that is known for its high resistance to thermal shock. First developed by Corning Inc. in the early 20th century, it became a staple in both scientific laboratories and household kitchens. The material's durability and versatility have made it a globally recognized product, though its composition has evolved over time with changes in manufacturing and ownership.

History

The development of Pyrex began at Corning Inc. in 1912, when scientist Jesse T. Littleton experimented with using a borosilicate glass casserole dish from the company's railroad signal lanterns. This innovation was spurred by the need for a more durable material than the tempered glass used in battery jars. By 1915, Corning introduced the first line of kitchenware under the Pyrex name, capitalizing on the material's ability to withstand rapid temperature changes. The brand's success was bolstered by its adoption in World War I for periscope lenses and later in the Apollo program for command module windows. Throughout the 20th century, Pyrex became an iconic American brand, featured in advertisements in Ladies' Home Journal and used in laboratories from MIT to the University of Cambridge.

Composition and properties

Original Pyrex was composed of borosilicate glass, a formulation containing significant amounts of boron trioxide and silicon dioxide. This composition gives it a very low coefficient of thermal expansion, approximately one-third that of soda-lime glass. Key properties include high resistance to chemical corrosion, excellent transparency, and the ability to withstand direct exposure to open flame on a Bunsen burner. The material's Young's modulus and hardness are comparable to other technical glasses, making it suitable for precise laboratory equipment like beakers and Petri dishes. These characteristics distinguished it from common container glass used for items like Mason jars.

Manufacturing process

Traditional borosilicate Pyrex was manufactured using a continuous melting process in large furnaces, often fueled by natural gas. Raw materials including silica sand, sodium carbonate, and borax were heated to temperatures exceeding 1600°C. The molten glass was then formed using methods like pressing, blowing, or drawing, depending on the product. For bakeware, the glass was often pressed into cast iron molds. The annealing process, critical for relieving internal stress (mechanics), was carefully controlled in lehr (glassmaking) ovens. This process was pioneered at Corning's facilities in Corning, New York, and later adopted by licensees like BSN Glasspack in France.

Uses and applications

Pyrex has a wide range of applications split between consumer goods and scientific instruments. In the home, it is famously used for pie plates, measuring cups, and refrigerator-to-oven casserole dishes. Its laboratory uses are extensive, including Erlenmeyer flasks, graduated cylinders, and condenser (laboratory) coils for distillation. The material's stability also made it valuable for industrial sight glasses, pharmaceutical vials, and astronomical mirror blanks, such as those for the Mount Palomar Hale Telescope. During World War II, it was used for searchlight lenses and gauge (instrument) glasses.

Safety and thermal shock

While highly resistant, Pyrex can fail through thermal shock if subjected to extreme, localized temperature differentials, such as placing a hot dish on a wet granite countertop. The original borosilicate glass formulation is more resistant to this than the soda-lime glass used for some consumer products after the 1990s. Safety concerns have prompted studies by the U.S. Consumer Product Safety Commission and warnings about avoiding use on direct stovetop burners. Proper use involves avoiding sudden quenching in cold water and checking for chips or cracks that can act as stress concentrators, principles also critical in materials science for ceramic cooktops.

Brand ownership and trademarks

The Pyrex trademark has been owned and licensed by several entities since its creation. Corning Inc. held the brand until 1998, when the housewares business was sold to World Kitchen, a company formed by Corning and Borden, Inc.. The rights for production in Europe have been held by Arc International since the 1950s, which uses the original borosilicate formula. In Brazil, the trademark is used by Nadir Figueiredo. This complex history has led to variations in product composition globally, a subject of discussion among consumers and in publications like Consumer Reports.

Category:Glass types Category:Kitchenware Category:American inventions Category:Corning Inc.