Why did such an important discovery occur so late in the … history of glass, and why was an accident necessary to bring it about?
     – Donald Stookey, 1977

Crystals are usually a glassmaker’s enemy. When they form in glass, crystals can change the properties of the material in unwanted ways. Corning chemist Donald Stookey saw crystals differently.

One night in 1954, he put a piece of experimental glass into a furnace. The next morning, he discovered that the furnace had overheated. He was sure he would find a pool of melted glass inside. Instead, he found an opaque solid that was so strong it bounced when he accidentally dropped it. Microscopic crystals had formed, changing the glass into a new material that Stookey called a glass-ceramic.

Stookey knew he could use heat and chemistry to control crystallization. Maybe it would be possible to form different crystals in different glasses. That would mean glass-ceramics could be tailored to have a remarkable range of properties. Stookey was right. Today, glass-ceramics are used to make everything from heat-defying cookware to exotic optical devices.

A Recipe for Glass-Ceramic

1. Make the glass, adding a special material—a nucleating agent—to the raw ingredients of the glass batch. The nucleating agent will later form microscopic particles called nuclei.
2. Heat the glass again. After nuclei form, crystal start growing around those nuclei.
3. The result is a new material, a glass-ceramic, with properties different from the original glass.

The secrets to making a glass-ceramic are material and heat control. Scientists select the exact ingredients and temperatures needed to make crystals grow in the glass. When enough crystals have formed, and reach the desired size, the glass melt is quickly cooled and becomes a new material: glass-ceramic.

The Corning Museum of Glass
This article was originally published in Innovations in Glass, 1999, pp. 56–57.

Published on October 25, 2011