Corning's Chemcor was a 1960s windshield glass nobody wanted — until the iPhone needed it

In 1960, Corning began Project Muscle — a research effort to develop chemically strengthened glass. Scientist Steven Kistler discovered that soaking glass in a molten potassium salt bath replaced smaller sodium ions with larger potassium ions, creating a compressive layer that made the glass dramatically stronger. By 1962, Corning had a working product called Chemcor. It was ten times stronger than ordinary glass.

Corning tried to sell Chemcor for car windshields, phone booths, and prison windows. The market was not interested. The glass was too expensive and too hard to manufacture at scale. Only about 100 Dodge Dart and Plymouth Barracuda racing cars ever used it in 1968. By the early 1990s, Chemcor was commercially dead. The technology sat on the shelf for nearly 45 years, a product that cost millions to develop and had no market.

In January 2007, Steve Jobs unveiled the first iPhone. The prototype had a plastic screen, and Jobs noticed scratches after carrying it in his pocket. He called Corning's CEO Wendell Weeks and said he needed a thin, strong, scratch-resistant glass — and he needed it in weeks. Weeks told Jobs about Chemcor. Corning adapted the formula, modified the manufacturing process, and shipped the first Gorilla Glass for the iPhone launch in June 2007.

Gorilla Glass became a fixture of the smartphone industry. By 2010, it was used in 20% of mobile handsets worldwide — about 200 million units. By 2012, over one billion devices carried it. By 2017, the number was five billion. The windshield glass that nobody wanted in the 1960s had become the most successful glass product in Corning's history.