After 4,000 years of development, you might assume that just about everything there is to be known about glassmaking has already been found out.
Though the basic recipe of sand, soda and lime remains the industry's core, first alchemists and then chemists have tinkered with the ingredients over the centuries to produce specialized products. For clarity and sparkle in tumblers and decanters, they added lead. For heat resistance in ovenware, they added boron. For a beautiful blue color in drinking vessels and decorative bowls, they added cobalt. To increase the speed at which light traverses it, as may be useful in an optical fiber, they added germanium. To reduce that speed, they added fluorine. And so on.
So when, one day in 2006, Steve Jobs, the founder of Apple, came knocking on the door of Corning, one of the world's biggest glassmakers and based in an upstate New York town from which it took its name, they were ready for him. The request was for a perfectly clear, tough and scratch-resistant glass to cover the screen of Apple's newly designed iPhone. Jobs, being Jobs, wanted it in six months.
Scientists at Corning's research center produce thousands of new formulations of glass every year. Some are promising enough to go to a small glassworks within the center, for trial production — but only a few make it to market. Everything that is learned, however, is filed away for a rainy day. A search in the archives in light of Jobs' request turned up a project from the 1960s to develop a toughened lightweight glass for industrial use. The new glass had been made in small volumes, but it never took off and was abandoned.
Corning reworked the formula to produce a strong, thin glass suitable for touch screens. They also reworked the name. And thus was born Gorilla Glass.
Gorilla Glass' selling point is not that it is tough, but that it stays tough when formed into sheets thin enough to protect the surfaces of the touch screens of today's increasingly skinny mobile devices without affecting those screens' function. That means permitting the circuits within a screen to locate the position of a finger placed on the surface.
In many portable devices that is done by detecting a tiny change in an electrical charge across the screen at the point where the finger touches. Too thick a screen can make this change harder to detect.
Since its launch, Gorilla Glass has been getting thinner and tougher still. According to Corning, a sheet less than 1 mm thick, made of the fifth generation of the stuff (the latest iteration, released last year), can survive four times out of five if dropped facedown from a height of 63 inches onto a rough surface. As a consequence, Jobs' job was but the first of many.
Gorilla Glass is now found in some 5 billion smartphones, tablet computers, laptops and other devices produced by electronics companies around the world. It is beginning to appear in other things, too, including cars — an ironic development, as the motor industry, one putative destination of the original version from the 1960s, had rejected it back then.
Two tricks give Gorilla Glass its strength. One is its composition — or, rather, the way that composition is modified in the middle of the manufacturing process. The other is a detail of this process itself.
The material starts off as a mixture of silica, aluminum oxide (a standard strengthening agent) and sodium oxide. This mix, once molten, is turned into a sheet using the "fusion draw" process, a technique pioneered by Corning. Fusion drawing involves pouring molten glass into a V-shaped trough and letting it overflow down the sides of that trough, clinging to them and running down them as treacle might cling to and run down the outside of a bowl.
As the two streams of glass meet at the bottom of the V their inner surfaces fuse into a single, thin sheet. Because the outside surface of each stream has had no contact with a production surface, those surfaces do not pick up any contamination or other damage, and emerge flat and devoid of defects. Materials break at their weakest point. For a sheet of glass that is often an impurity, crack or scratch on its surface. Fusion drawing eliminates such weakness.
Gorilla Glass dominates the market for cover glass for electronic equipment and Corning is pushing it, and other specialist glasses made by fusion drawing, into more areas.
According to Jeffrey Evenson, the firm's chief strategy officer, tough, lightweight glass opens up new possibilities for giant display screens and for use as part of the architecture of buildings. Entire walls and tabletops could become displays with touch-sensitive surfaces. Windows, too, will contain electronic layers, allowing their transparency to be tweaked as desired — and perhaps even permitting them to gather solar energy from nonvisible frequencies, to generate electricity. Other types of glass will become more flexible, enabling portable devices to be bendable, or even foldable.
One of the biggest areas for growth, Evenson reckons, will be in cars. Already, instruments and switches on the dashboards of new cars are being replaced with touch screens. As glass can be formed into different shapes, these screens can be curved into the contours of a vehicle's interior. But Gorilla Glass, or something like it, could also be employed to make car windows.
These, being thinner than existing windows, would be lighter and thus save fuel or, in a battery-powered car, electricity. A version of Gorilla Glass is already being used for the windscreen of Ford's GT sports car. Ford reckons the new glass is about 30 percent lighter than what it is replacing. It is also stronger, and scratch-resistant. Further ahead, electronics could be incorporated into the glass, to project images onto the windscreen, to assist drivers.