Sapphire phone screens not as strong as you think, says Corning

Sapphire-schmapphire, says the Gorilla Glass-maker, whose strength test challenges claims that sapphire makes the stronger smartphone.

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On the surface, smartphones screens made of sapphire sound superb -- they're naturally strong, extremely scratch resistant, can withstand flexing, and transmit light very well. That's the widely accepted story, at least.

Disputing this view is Corning, maker of the Gorilla Glass material that covers a majority of smartphone screens.

Corning, whose aeronautics branch has worked with lab-grown sapphire since the 1970s, says it tested the strength of sapphire claims -- a potential cover glass alternative -- in-house.

Corning's conclusion: that sapphire, the world's second-hardest material after diamond, just can't take the lumps that a large smartphone screen has to bear. Sapphire is fine for protecting watch faces and camera lenses, Corning says, but isn't as optimal for phones.

To demonstrate weaknesses in the rival material, Corning says it ran strength tests on a sample of its toughest Gorilla Glass 3 material and also on a sample of lab-grown sapphire.

Let me note before moving on that Corning hasn't shared a detailed report of its test results, and, at the time of our interview, hadn't planned to work with an independent testing outfit to confirm its findings. In other words, this was Corning's test, developed and run in Corning's own lab.

Jeff Evenson, Corning's senior vice president and operations chief of staff, said that sapphire came out ahead in resistance to macro-scratches, an important factor in warding off breaks, but not in a tumble test -- where the device spins for 45 minutes and picks up scratches that weaken its structure -- before succumbing first in a ring-on-ring pressure test.

The tumble test is a common industry stress test that simulates typical wear; for instance, if you put your phone in your pocket or purse alongside other objects.

Corning's in-house video:

Gorilla Glass is also lighter, thinner, much cheaper to make, and transmits light better, Corning's Evenson told CNET. Evenson called sapphire "brittle," and warned that breaking it could cause serious cuts to human skin. Corning does not intend to produce a sapphire cover material for smartphones and other electronics to replace its Gorilla Glass line, the company said.

I had an opportunity to take a good, hard whack at a sapphire smartphone screen last March at Mobile World Congress. In this case, I was looking at a screen protector sitting on top of an iPhone, the whole thing surrounded by a sturdy iPhone case. It wasn't clear how thick the protector was, but the screen seemed bright and was very responsive to my touch, even on top of the regular iPhone cover material (which is Gorilla Glass, I should point out).

GT Advanced Technologies, the company that orchestrated the Barcelona demo, is one firm that operates the production of the sapphire crystalline material. In addition to cooking up crystals, it's also concocting ways to make make sapphire sheets far thinner and lighter than they are today -- thinner even than today's iteration of Gorilla Glass, perhaps.

During the sapphire demo in Spain, I was also able to repeatedly bash and rough up the protector's surface without damaging the sapphire screen at all. True, that was a staged test meant to impress -- and it did. Corning's video is similarly convincing.

Without a third-party lab producing an in-depth report of scientific, industry-standard strength tests -- or samples of both materials at the ready for CNET's own torture testing -- it's harder to get a grip on exactly where each material excels and where it falls shorter than its competitor. I hope one day soon CNET will be able to watch or even perform these tests in person.

The one thing I will say is that this escalating cover material rivalry makes it clear there's much more room for growth in protecting your smartphone from its owner -- you. Just how clear is this, exactly? Crystal.

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About the author

Jessica Dolcourt reviews smartphones and cell phones, covers handset news, and pens the monthly column Smartphones Unlocked. A senior editor, she started at CNET in 2006 and spent four years reviewing mobile and desktop software before taking on devices.

 

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