Today’s “Planet Earth Report” –“Humans Have Been Making Glass for Millennia and We Still Don’t Have a Good Idea of What It Is”



To reach you, these words were encoded into signals of light moving about 125,000 miles per second through fiber-optic cables. These lines, splayed out across mountains and oceans, are made of hair-thin glass 30 times more transparent than the purest water. The technology was made possible in part by a team from Corning Incorporated. In 1970 they patented a type of cable that could transmit large amounts of information long distances, building on decades of work by other researchers.

Assuming you’re reading this on a smartphone, writes Doug Main in today's Atlantic, you also owe a debt to Steve Jobs, who in 2006 asked Corning to make a very thin, strong screen for his new product, the iPhone. The result, Gorilla Glass, now dominates the market for mobile devices: Phones made with the fifth generation of this product can be dropped onto a rough surface from a height of five feet (selfie height) and survive 80 percent of the time.

That’s just the start. Without glass, the world would be unrecognizable. It’s in the eyeglasses on your face, the lightbulbs in your room, and the windows that let you see outside. But despite its ubiquity, there’s still some debate within the research community about how to define “glass.” Some tend to emphasize its solid qualities, others its liquidity. Unanswered questions abound, like what makes one type of glass stronger than another, or why certain mixtures produce their unique optical or structural properties. Add to this the nearly infinite varieties of glass—one database lists over 350,000 types of currently known glass, though in principle the number of mixtures is limitless—and you get a surprisingly large and active field of research that regularly produces astounding new products. Glass has shaped the world more than any other substance, and in many sneaky ways, it’s the defining material of the human era.

 “We’ve been making glass for thousands of years, and we still don’t have a good idea of what it is,” says Mathieu Bauchy, a glass expert and materials researcher at UCLA. Most glasses are made by heating and then quickly cooling a mixture of ingredients. In the case of flat glass, which makes up windows, that mixture may include sand (silicon dioxide), lime, and soda. Silicon provides the transparency, calcium provides the strength, and soda reduces the melting point. The swift cooling process doesn’t allow for atoms to form a regular pattern, explains Steve Martin, a glass scientist at Iowa State University.

That helps explain why glass is neither a crystalline solid nor a liquid, but rather an atomically disordered (or amorphous) solid. The atoms within want to reassume a crystal structure, but typically cannot because they are essentially frozen in place. You might have heard that cathedral windows flow over long periods of time, hence why some are thicker at the bottom. That’s false: Such windows were made that way, due to a manufacturing technique that involved spinning molten glass that created uneven patches. But glass does move; it just does so very slowly. A study published last year in the Journal of the American Ceramic Society estimated that room-temperature cathedral glass would take over 1 billion years to flow a single nanometer.

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