Finding the Right Recipe: Borosilicate Glass

Finding the Right Recipe: Borosilicate Glass

Otto Schott, the pioneering German glass chemist, made a glass that could reliably do something that didn’t seem possible: endure sudden, uneven temperature shifts without shattering. The key, Schott discovered in 1882, was to have a critical amount of the element boron in the glass recipe. Schott’s new durable, heat-resistant borosilicate glass was an immediate commercial success.

Building on Schott’s work, Corning chemist W. C. Taylor found the right recipe to make an even more temperature-tolerant borosilicate glass. With it, railway signal lanterns didn’t shatter in sleet or freezing rain. By 1915, Taylor and chemist Eugene Sullivan had transformed borosilicate glass into an exotic new product--Pyrex® glass cookware. It captured America’s imagination. Soon, in kitchens all over the country, people were cooking in glass.

Schott’s and Corning’s work launched the era of modern glass chemistry research. Today, there is a “cookbook” of more than a million different glass recipes, each precisely formulated to meet a product need.

Baking a New Business

Pyrex advertisement 1916

When physicist Jesse Littleton joined Corning Glass Works in 1914, the company was using its new heat-resistant glass to make battery jars and signal lanterns. Littleton’s job was to evaluate the properties of the new glass. One day, his wife’s ceramic casserole dish cracked. Bessie suggested that the heat resistant glass might be just right for baking. Jesse went to the lab and sawed off a battery jar. He gave it to his wife, who successfully baked a cake in it.

Bessie continued baking in battery jars, and even made custards in lamp chimneys. Her kitchen experiments provided the impetus for a new consumer-product business—see-through Pyrex® glass cookware.

Good Vibrations

Pyrex® labware

Heat causes atoms in glass to vibrate—they alternately move farther apart, then closer together.  The higher the heat, the greater the vibrations. If the vibrating atoms move away from each other more than they move together, the glass expands.  When glass is heated unevenly, some parts expand more than others, and the glass usually shatters.  The element boron can prevent that.

In the right amount, boron moderates the vibrations. It makes the distance between atoms grow and shrink by almost the same amount; the net movement of the atoms is nearly zero. There’s little expansion, so the glass doesn’t shatter.

Low-expansion borosilicate glass was developed in Germany to make thermometers that would resist changing their volume with temperature changes. In America, the new glass was first used for railroad signal lanterns that wouldn’t shatter with changes in the weather.

Published on October 20, 2011