In the spring of 2007, one man looked at the screen of his future phone, saw scratches—and set off a chain reaction that, within a few months, turned a forgotten technology from the sixties into a material without which it is now impossible to imagine a single smartphone.
In January 2007, Steve Jobs stepped onto the Macworld stage and showed the world a device he called a revolutionary product. The first iPhone’s screen—3.5 inches diagonally—was covered in plastic. It was the standard choice: plastic screens were fitted to the overwhelming majority of mobile phones at the time, from Nokia to Motorola. They were light, cheap, familiar to production lines. No one in the industry considered plastic a problem.
Jobs did. Somewhere between the January presentation and the planned June 2007 launch, he reportedly carried an iPhone prototype in his pocket—along with his keys, as anyone would. The plastic became covered in fine scratches. For a device whose entire concept was built around direct contact between finger and screen, around tactile intimacy between human and interface, a clouded surface was not a cosmetic flaw but a subversion of the very idea. Jobs demanded that the plastic be replaced with scratch-resistant glass. There were only a few months left before sales began.
The demand sounded like a whim, but behind it lay the simple physics of everyday life. Resistive touchscreens, then used in PDAs, required pressure from a stylus—the user barely looked at the surface; they looked through it. The iPhone’s capacitive screen was different: the finger glides across the glass, the eye fixes on its surface, every scratch like a crack in an eyeglass lens. Plastic, which had served button phones for years, proved inadequate for this new kind of interaction.
The request reached Corning quickly: two days later, Corning CEO Wendell Weeks personally called Jeff Williams—who ran Apple’s operations in 2007 and would not receive the title of chief operating officer until 2015—and opened with a line that has since entered the corporate folklore of both companies: “Hi, your boss called and said my glass sucks.” Corning—a company headquartered in a small town in upstate New York—was then known primarily for fiber optics and glass-ceramic cooktops. But its archives held something few people remembered outside materials-science circles.
In 1962, Corning launched Chemcor—a line of chemically strengthened glass the company offered to the automotive industry, pharmaceuticals, and eyewear manufacturers. The idea was elegant: instead of making glass thicker—and therefore heavier—you could alter its surface structure at the molecular level, creating internal stress that resisted external forces. Chemcor did work—the glass was many times stronger than ordinary glass. But the market did not respond. Carmakers had enough with tempered glass, which was cheaper. There simply was no mass demand for thin, ultra-strong glass in a world where screens were cathode-ray tubes and phones were wired. In 1971, the project was shelved.
More than thirty years later, in 2005, Corning engineers returned to the work done on Chemcor. Mobile phones were getting thinner, screens larger, and the company began exploring the prospects of reviving the technology. The gorilla entered this story later: Corning introduced the Gorilla Glass brand to the public only in 2008, when the material was already in mass production. The work in 2005 remained a research phase—without a specific client and without deadline pressure. When the call from Apple came, Corning found itself in a rare position: the technology existed, the fundamental research had been done, but there was no mass production. Between a laboratory sample and millions of units lay an abyss that had to be crossed in a matter of weeks.
What fascinates me is the mechanism itself—the way chemistry makes a brittle material resilient without changing its appearance. Ordinary window glass is, roughly speaking, solidified silica melt with sodium and calcium additives. It is transparent, hard, but brittle: microscopic flaws on the surface—and they are always there, from dust, from touch, from the manufacturing process itself—become points where stress concentrates. A crack begins with an invisible scratch and spreads instantly, because nothing inside the material resists it.
The aluminosilicate glass Corning was preparing for the iPhone was built differently. Some of its silica is replaced with aluminum oxide, producing a denser, more ordered structure. But the real magic happens after forming: the finished glass is immersed in a bath of molten potassium salt—potassium nitrate, KNO₃—heated to around 400 °C. At that temperature, ions begin to migrate. Sodium ions sitting in the glass’s surface layer are small—their ionic radius is about 0.95 angstroms. Potassium ions in the melt are larger—about 1.33 angstroms. Potassium pushes sodium out of its positions in the crystal lattice and takes its place. But those positions were designed for a smaller atom.
The effect is easiest to imagine like this: you are trying to cram a watermelon into a bowling-ball hole. The larger potassium ions, wedged into narrow positions, create immense residual compression in the glass’s surface layer. That layer—tens of microns thick—is constantly under inward-directed pressure. Before a scratch can turn into a crack, it must first overcome that compression, and only then break through into the depths. In essence, the glass receives invisible armor that adds no thickness and reduces no transparency.
But there is a crucial nuance here, one often lost in marketing descriptions. Scratch resistance and impact resistance are different properties. The compressed surface layer is excellent at resisting abrasion: keys in a pocket, grains of sand, fingernails. But when dropped from a height, glass experiences not abrasion but impact deformation—a sharp, localized blow that can exceed even a strengthened material’s breaking point. Ion exchange does not make glass ductile; it remains brittle in the physical sense of the word. When strengthened glass does break, it can shatter even more violently than ordinary glass—the stored internal stress is released all at once, like a spring.
It is one thing to know how to strengthen glass. It is another to make it in millions of sheets at the required thickness, with the required optical purity, on the required schedule. The first iPhone needed glass 1.3 millimeters thick—thinner than most samples Corning had made under Chemcor. Thin glass is harder to form, harder to transport, harder to cut.
Corning used fusion draw technology—the fusion process—developed by the company back in the 1960s to produce flat glass without mechanical polishing. The principle resembles a waterfall flowing down both sides: molten glass is fed into a V-shaped trough, an isopipe, spills over its edges on both sides, and flows downward, joining at the bottom edge into a single sheet. Neither outer surface of the sheet ever touches the forming elements—they are formed in air, producing exceptional smoothness without additional processing. For a touchscreen, where a finger must glide without resistance and the image beneath the glass must remain crystal clear, this was critically important.
Corning’s plant in Harrodsburg, Kentucky, was retooling its production lines for the new format. I find it hard to imagine the scale of the engineering pressure: they had to simultaneously control the chemical composition of the melt, the temperature profile of the forming process, the draw speed—which determines sheet thickness—and then the ion-exchange conditions for sheets of an unfamiliar format. Every parameter affected the others. Cool too quickly, and the glass develops the wrong kind of internal stress. Leave it in the potassium bath too long, and the ions penetrate too deeply, reducing the compression effect at the surface. Corning managed it, though the company has been sparing with the details of that manufacturing race.
Apple’s task was no less of a puzzle. The glass had to be integrated into a stack of several layers: the LCD display itself, the capacitive touch layer, optically clear adhesive, and a protective coating. Each layer contributed its own reflections, refraction, and brightness loss. Glass 1.3 mm thick instead of a thin plastic film changed the optical path, added weight, and required a different method of attachment to the casing. The first iPhone’s aluminum frame, to which the glass was bonded, had to compensate for the difference in thermal expansion coefficients between metal and glass—otherwise, when heated by the processor or the sun, the adhesive bond would begin to degrade.
And now—a fair counterfactual history. What if the plastic had remained?
The first iPhone would most likely still have become a hit. The device’s revolutionary nature was defined by its software platform, multitouch interface, and iTunes ecosystem, not by its cover material. The iPod—a device Apple was already selling by the tens of millions—had a plastic screen and plastic body, and buyers put up with scratches by purchasing cases and screen protectors. By 2007, the iPod accessories market was already enormous, and an iPhone with a plastic screen would likely have spawned a similar industry of films and covers even faster.
But this is what would have changed in people’s perception. A plastic screen clouds over after a few months of active use. For a device priced at $499—the launch price of the 4 GB model in June 2007—a cloudy screen creates cognitive dissonance: you pay for a premium product, yet it looks worn out faster than a cheap phone with a little display window. The feeling of an “expensive, fragile toy” would have taken root sooner and more firmly. Critics—and there were plenty of them in 2007—would have gained a tangible argument: why pay so much for a phone that, after six months, looks like a cat has been chewing it?
There is another line of possibility. If Apple had not bet on glass, Corning would not have had the decisive commercial incentive to scale up production. The company might have continued its research under the Gorilla Glass codename in laboratory mode for several more years. Other smartphone makers—Samsung, HTC, LG—began switching to strengthened glass in 2008–2009 largely because Apple had already proved the solution viable and Corning already had a functioning production line. Without Apple’s order, the chain could have shifted by one, two, three years. The Gorilla Glass brand, which Corning officially introduced in 2008, might have appeared later—or never appeared in that form at all—because without the iPhone success story, the name’s marketing value would have been lower.
That said, plastic should not be demonized. Samsung released flagships with plastic screens for several years after the first iPhone—Galaxy S had glass in 2010, but many models in the line continued to use polycarbonate in their bodies. Plastic is lighter, cheaper, and does not shatter when dropped. Its main drawback is precisely its vulnerability to abrasion, the softness of its surface. In a world where we touch a screen hundreds of times a day, that drawback proved decisive—not because plastic is a bad material, but because the nature of contact between human and device had changed.
After 2008, the Gorilla Glass brand became one of the few component brands known to the end consumer—like Intel Inside for processors. Corning released several generations of the material, each time increasing the depth of the compressed layer, experimenting with compositions, adding drop resistance—which the first generation, honestly, barely provided. By the mid-2010s, strengthened glass had become such a standard component that its absence from a smartphone’s specifications was seen as suspicious corner-cutting.
There is one detail in this story that I like: the technology that sat in Corning’s archives for almost forty years was neither forgotten nor lost. It was premature. In the sixties, the world had no need for thin, ultra-strong glass—automotive windshields managed perfectly well with tempering, consumer electronics made do with cathode-ray tubes, and mobile phones did not exist. Chemcor was a solution for which the problem had not yet been invented. The problem appeared at the moment when the human finger became the primary input tool and the screen the primary surface of interaction.
Ion exchange in a potassium bath, fusion draw in Harrodsburg, scratches from keys in Jobs’s pocket—all of these are links in one chain, in which materials science, consumer psychology, and manufacturing logistics became woven so tightly that they can no longer be separated. Every time I run my finger across my phone’s screen and see a sharp image beneath the glass without a single scratch, I remember that this surface is the result of a process conceived in 1962, forgotten, resurrected, and brought to mass production over a few panicked months in 2007. Corning still makes protective glass at the same Kentucky plant, and potassium ions still displace sodium ions in hot baths—there are simply orders of magnitude more of those baths now.