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 forms microscopic particles called nuclei
2. Heat the glass again. Crystals will grow on the nuclei.
3. The result is a new material, a glass-ceramic, with properties different from the original glass.

The secret to making a glass-ceramic is control. Scientists select the exact temperatures and ingredients needed to make crystals grow in the glass. When enough crystals have formed, the glass becomes a new material: glass-ceramic.