Borosilicate Glass: How U.S. Borax Helped Develop the Glass Industry

:: Wednesday, April 11, 2018 :: Posted By Allen Zheng

Formed by the evaporation of seasonal salt lakes, the first deposits of borax were discovered in Tibet. Around the 8th century, traders brought borax along the Silk Road to the Arabian Peninsula where it was used in metallurgy. The quantities traded were small, its method of production was secret, and its source remained a mystery to those outside the trade. Although a precious and expensive commodity, borax became popular during the Middle Ages in Europe as a flux for soldering and in the refining of metals and assaying of ores.

Early Borosilicate Glass

The earliest reference to borosilicate glass (glass made from a mixture of silica and boric oxide) comes from China, where Zhao Rukuo described glassmaking by Arabs and others in 1225: "Borax is added so that the glass endures the most severe thermal extremes and will not crack." The earliest European mention of borax in glass occurs in a German work by Johann Kunckel in 1679, giving recipes for artificial gems.

In 1739, another German, Johann Cramer, recommended this recipe for crystal glass:

  • 3 parts of prepared flints (silica)
  • 1 part of purest alkaline salt (potash)
  • 1 part burnt borace (borax)

British author Robert Dossie wrote in 1758 that the best looking glass plates contained 56% white sand, 23.5% pearl ashes (potash), 14% saltpeter, and 6.5% borax. He also noted that borax helps glass receive certain colors.

During the 18th century, glassmakers in many parts of the world began to understand the properties of borax, but its price—£750 a ton in London in 1750—remained far too high for general application. Then in the 19th century, technical developments in the industry coincided with new borate discoveries in Italy, Turkey, and the Americas, which led to substantial reductions in price. Borax cost less than £100 a ton in 1850, and less than £20 by the 1890s. For the first time in history, borax became viable for modestly priced, mass-produced goods.

Glass Science: The Borosilicate Glass Breakthrough

A scientific understanding of the way in which boric oxide could enhance the quality and performance of glass itself first began when Otto Schott persuaded his colleagues from the University of Jena—Ernest Abbe and Carl Zeiss—to form the Schott & Associates Glass Technology Laboratory in Jena, Germany, in 1884.

Up to this time, there were only six elements commonly used in glass: silicon, oxygen, sodium, potassium, calcium, and lead. Schott and Abbe systematically investigated the introduction of a wide range of chemical elements into glass compositions. From this work, they found that in the visible spectrum, glass containing boric oxide affected short wave length dispersion, so that it became a valuable constituent of optical glasses.

Borax in glass enhances appearance, thermal shock resistance, and durability.

Schott and Abbe succeeded where others had failed in improving the optical properties of glass and at the same time increasing its resistance to water and chemical attack. They also discovered that glasses containing boric oxide could be formulated to withstand sudden changes in temperature. Most importantly, they were able to consistently replicate these properties. This led to the mass commercial manufacture of many products based on borosilicate glasses.

They invented a group of borosilicate glasses that were resistant to thermal shock and suitable for the chemical laboratory. The company became a leading supplier of laboratory glassware worldwide. Later, they added pharmaceutical products, including syringes, to their line. Their mass production of lamp cylinders helped gas lighting become practical.

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The director of research for Corning Glass Works, Eugene Sullivan, brought Schott’s work in borosilicate glass to the United States. Sullivan developed a low-expansion borosilicate glass to reduce breakage in Corning’s railroad signal lanterns and battery jars. With the outbreak of war in 1914, supplies of laboratory glassware from Germany were no longer available, and Corning became a new center for the production of borosilicate glasses.

When Sullivan’s colleague, Jesse Littleton, brought home a casserole dish made of Corning’s low-expansion borosilicate glass, a new form of cookware was born. In 1915, Pyrex was introduced to the American public. With that, the modern era of borosilicate glass technology began.

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U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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