Apple’s massive investment in a new Sapphire Glass factory in Arizona hints at a new Sapphire-screened iPhone 6, or potentially a new substance to be used for the iWatch.

But Sapphire Glass has come under fire from Corning, the makers of Gorilla Glass. This is the glass currently used on the iPhone and most other smartphones.

What is Sapphire Glass?

Sapphire Glass new type of clear screen that Apple introduced with the iPhone 5s. However, it isn’t used on the main display but the Touch ID Home Button. This is actually a clear see-through mini screen with a camera behind it that scans your finger. According to Apple, “The button itself is made from Sapphire Crystal, one of the clearest, hardest substances known to man. It protects the sensor and acts as a lens”.

Where it gets interesting is that Apple seems to be gearing up to make Sapphire Glass in huge quantities. But why? What is Sapphire Glass and why  is it is important to Apple?

Sapphire Glass not actually glass for starters. As the name suggests its Sapphire, synthetic Sapphire to be precise. fine alumina powder is added to an oxyhydrogen flame,. The process was invented in 1902 by French chemist Auguste Verneuil.

Sapphire Crystal is astonishingly sturdy. Sapphire has a value of 9 on the Mohs scale of mineral hardness, which puts it in the same place as titanium carbide. For reference 1 is talc and 10 is diamond. So Sapphire Glass is pretty sturdy stuff.

If you want to know what other Apple brands and related tech terms mean, take a look at our Apple user's jargon buster. See also:

Sapphire Glass used for Touch ID

How is Sapphire Glass made?

According to GT Advanced Technologies, it’s new Sapphire furnace “produces high-quality, large-area sapphire substrates for applications that demand the highest grade sapphire material such as high brightness LEDs, consumer electronics and industrial applications.”

Apple is rumoured to have invested $578 million in GT Advanced Technologies to create its new plant in Arizona.

See: Apple allegedly spent $578 million to speed up development of iPhone 6 sapphire display

How is Apple Glass Made

What is Apple using Sapphire Glass for?

Currently the Sapphire Glass is only used in a small part of the iPhone (the Touch ID Sensor in the iPhone 5s) but Apple has made it clear that it is planning to use more, a lot more, Sapphire Glass.

See: iPhone 6 release date, rumours & leaked images: new leaked photo shows iPhone 6 with borderless display

Will Apple use Sapphire Glass on the iPhone 6?

Apple’s Tim Cook revealed during the latest annual shareholder’s meeting that Sapphire Glass is to be used in an upcoming secret project. Cook said that the new Arizona plant would be used "extensions of what we're already doing" and for "things you can't see".

Those “things you can’t see” most certainly include the iPhone 6. Given the size and scale of Apple’s Arizona investment it is certainly planning to move Sapphire Crystal away from the Touch ID Home Button and out towards the screen.

Sapphire Glass screens

Will Apple use Sapphire Glass for the iWatch?

The other thing to consider is that Apple could use the Sapphire Glass on another product line entirely. The two big Apple rumours remain an Apple iWatch and Apple Television. Sapphire Glass, obviously, makes no sense for a television but Sapphire Glass’ sturdy quality could make it a good choice for the rough-and-tumble that a iWatch. Especially if the iWatch is, as rumoured, heavily centred around health and fitness.

See: Apple iWatch release date, rumours & images - 200 people working on iWatch with health & fitness focus

Will Apple use Sapphire Glass for the iPad?

Whether Apple starts to use Sapphire Glass on its iPad instead of Gorilla Glass will depend on how much it can make, and how much it costs Apple to make Sapphire Glass. We are assuming that it will first roll out on the iPhone and then on the iPad, but Apple could make a stand and roll it out to all new devices at once. We expect a future generation of iPad to use the same Touch ID sensor that is found on the iPhone, so that will use Sapphire Glass.

How is Sapphire Glass made?

In November Apple announced that is was building a plant in Mesa, Arizona to create Sapphire Glass. Apple is working with GT Advanced Technologies and together they to create around 2,000 jobs in the area. Investor Matt Margolis has predicted that Apple’s new Arizona plant could produce around 100 to 200 million five-inch sapphire displays per year. Apple is rumoured to have invested

“Apple is indisputably one of the world’s most innovative companies and I’m thrilled to welcome them to Arizona,” said Arizona Governor Janice Brewer. “Apple will have an incredibly positive economic impact for Arizona and its decision to locate here speaks volumes about the friendly, pro-business climate we have been creating these past four years. Their investment in renewable energy will also be greening our power grid, and creating significant new solar and geothermal power sources for the state.”

What is Gorilla Glass

Gorilla Glass is the brand of scratch resistant glass currently used for the display of the iPhone. Apple has used Gorilla Glass as the glass for its products ever since Steve Jobs insisted that the iPhone’s display be made of glass and not plastic. Normal glass scratches too easily for touch-screen display and somebody suggested he met up with NY-based company Corning. They hold the patent on Gorilla Glass.

Unlike Sapphire Crystal, Gorilla Glass is actually made from glass. The process involves placing glass in a bath of molten salt, as it cools small sodium ions leave the glass, and potassium ions replace them. This creates a tough scratch resistant layer to the glass.

The process has been used since the 1960s, but it wasn’t until Apple came along that it really found a home.

Why does Apple use Gorilla Glass?

Steve Jobs personally met up with Corning’s CEO Wendell Weeks in 2006 to talk about the glass. The story goes that Jobs was impressed and said he wanted enough of it within six months for every iPhone. Weeks told him that the company wasn’t set up to mass produce it, but Jobs said (in typical Jobsian fashion) “Don’t be afraid. You can do this.” On the launch of the iPhone Jobs sent Weeks a letter saying “we couldn’t have done it without you” and that letter remains framed on his desk.

Gorilla Glass vs Sapphire Glass: Strength

Unsurprisingly Corning isn’t quite as enamoured with Apple’s new Sapphire Crystal plant as Arizona’s Governor. Corning senior vice president Tony Tripeny listed the problems with sapphire during a session at Morgan Stanley's Technology, Media & Telecom Conference. He told them: “The formation takes about 4,000 times longer than Gorilla Glass at a significantly higher melting temperature. Its hardness makes machining more difficult and costly. Then the cost per unit increases exponentially because when you have defects in boundaries in the crystal growth process, you essentially cut them out. And so unlike glass, where we have developed technologies so that we can have [a] very large pristine pieces of glass, when you have that on crystals, what you end up doing is always having a yield issue. So it is really those items that make things more expensive.”

So to summarize:

  • Sapphire Glass costs roughly 10 times more than Gorilla Glass.

  • Sapphire Glass is roughly 1.6 times heavier than Gorilla Glass.

  • The manufacturing process is not environmentally friendly because it takes about 100 times more energy to generate Sapphire than Gorilla Glass.

  • It transmits less light. This means either the screen will be dimmer, or it will have to use more power.

  • While scratch resistant, Sapphire breaks under less pressure than Gorilla Glass (according to a Corning test).

Tripeny told Morgan Stanley "when we look at it, we think from an overall industry and trend that is not attractive in consumer electronics."

Is Gorilla Glass 3 stronger than Sapphire Glass?

Corning also claims that its latest iteration, Gorilla Glass 3, is stronger than Sapphire Glass.

Jeffrey W. Evenson, senior vice president, remarked, “Discussion seems to center around sapphire as an obvious solution for a cover material. What would people say if someone invented a cover that was about half the weight, used 99 percent less energy to make, provided brighter displays, and cost less than a tenth of sapphire? I think they’d say that sapphire was in real trouble. It so happens that we at Corning already invented that cover – and it’s called Gorilla Glass.” Evenson added that the company’s tests so far indicate Gorilla Glass requires about three times more force to break than sapphire after both materials have received similar wear and tear.

Is Sapphire Glass going to be too expensive?

Apple is reputed to have spent around $578 million on its Sapphire plant in Arizona, and the company isn’t known for making big investments or foolish investments. While Sapphire may currently costs 10 times more than Gorilla Glass that may quickly change once full-scale production starts, and Apple will control the production directly which is always an area that interests tim Cook.

Is Apple’s Sapphire Glass plant bad for the environment?

As for the environmental claims we’re not sure they stand up in light of Apple's . As a commenter on this Motely Fool website says “Apple's plant will be using renewable energy. How much renewable energy does Corning use producing Gorilla Glass?”

The story with the light efficiency is the same. Sapphire may allow a couple of percentage points of less light through than glass, but Apple’s screens and batteries are much more efficient on the latest models than on the original iPhone. We think Apple will have tested Sapphire and found it works the same. Again, this depends on what kind of device Apple is making: an iWatch may simply not need as vibrant a display as an iPhone (you’re not going to watch video on it).

Why is Apple switching to Sapphire Glass?

If it is true that Sapphire isn’t really stronger than the latest iteration of Gorilla Glass (and without the ability to perform independent testing we really are having to take Corning’s word over Apple’s silence.) Most other reports we’ve heard suggest that Sapphire Crystal is at least three times as strong as Gorilla Glass 3. We actually think either technology would be sufficient protection for the current range of Apple devices.