Apple’s long-awaited announcement of its new iPhone 6 and iPhone 6 Plus last fall came with an unexpected twist: Contrary to rumors, the company opted not to use an ultra-strong glass called sapphire for the devices’ screens. That was startling because Apple was involved in a major deal with sapphire company GT Advanced, ostensibly to provide the material for Apple’s newest phones.

After Apple announced its sans-sapphire iPhones, it was revealed that GT Advanced couldn’t deliver the amount of the material Apple required on time because of production issues. In a column I wrote last fall, I said Apple never planned to put sapphire screens in the iPhone 6 regardless of GT Advanced’s problems. However, it turns out that Apple did in fact enter into the GT Advanced deal wanting to use sapphire screens in its new iPhones, but by late 2013, the company realized that issues at GT Advanced meant that just wasn’t going to happen. Apple changed direction at the beginning of 2014, when it began working with Corning to deliver its newest version of Gorilla Glass for use on the iPhone 6.

Not long after the iPhone 6 was announced, the relationship between Apple and GT Advanced imploded, with the latter filing for bankruptcy. As of today, there’s no indication Apple is still seeking sapphire screens for any new iPhones — but its patent filings mean it’s impossible to rule out this possibility.

But there are other reasons sapphire won’t see the light of day in smartphones. First, it’s incredibly difficult to make sapphire screens in serious quantities at a cost that would make them feasible for even top-of-the-line smartphones. Also, the smartphone market’s trend toward bigger screens is making sapphire even more expensive to produce and buy.

I recently recorded a podcast with two professors of material sciences that helped me gain a better understanding about the costs and difficulty involved with creating sapphire screens in volume. Joining me in this discussion were Richard Lehman, a professor and chair of Rutgers University’s Advanced Polymer Center, and Dr. Helen Chan, chair of Lehigh University’s Department of Materials Science.

You can listen above, but here are some of the key points we discussed:

Glass is used in almost all smartphone screens, and is a great solution. Lehman pointed out that sapphire is used in watches and products that have a long life. But because smartphones have a lifespan of 18 to 24 months, the extra cost involved may not be worth it for most consumers.

Lehman said glass costs about a nickel per square inch to manufacture, while sapphire costs several dollars per square inch to make. He also pointed out that manufacturing glass is highly scalable, while Dr. Chan explained that it takes a 2,000-degree furnace to melt sapphire, which has a serious impact on the environment.

While both professors are not experts in manufacturing, they brought up key points on the virtue of sapphire as a potential material for screens, but questioned anyone’s ability to make these screens in large volumes. In addition to the melting process, sapphire must be cut razor-thin and subjected to extra polishing, according to Chan. It takes at least four different steps or procedures to produce each sapphire screen.

The issue of transparency came up, too. Lehman pointed out that with sapphire, “there is a high reflective index involved that cuts down on the transmission through the screen and it also could give glare.”

Lehman said Corning’s new Gorilla Glass 4 is twice as tough as Gorilla Glass 3, providing 80% more protection in standard tests on survivability.

The professors also pointed out that hardness (a key attribute of sapphire) might not be the best way to go with next-generation smartphones. Here’s a video from that illustrates this point well and explains the breaking point of glass compared to that of sapphire:

https://www.youtube.com/watch?v=kVQbu_BsZ9o

Although the podcast and the video explore the possibility of using sapphire as a screen material for smartphones, they reinforce the idea that the long-term prospects of sapphire screens on smartphones just aren’t viable. Given the additional costs to make a sapphire screen and the increasing strength of more traditional glass, anyone pursuing sapphire for use on smartphone screens would be up against some pretty formidable challenges. For sapphire to be the future, we’d need to see a major breakthrough in its manufacturing process — and from what I can tell, that just won’t happen in the near future.

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