Everything You Wanted To Know About Sapphire Glass, But Were Afraid To Ask [Q&A]


Sapphire glass was in the news again today, thanks to a jump in the share price of GT Advanced Technologies Inc. — the company which will reportedly manufacture the iPhone 6’s sapphire display.

With contrasting reports about sapphire’s advantages over Gorilla Glass, along with counter-reports from Gorilla Glass maker Corning, we figured the time was right to break down some of the questions about Apple’s latest wonder-material.

Currently used by Apple only in small quantities in the protective glass over the iPhone 5s camera sensor, and Touch ID home button, analysts predict that worldwide demand for sapphire glass is about to pick up in a big way.

Apple announced late in 2013 that it was planning to open a sapphire glass manufacturing facility in Arizona — employing 700 people, and capable of churning out between 100 million and 200 million iPhone displays each year. GT Advanced Technologies will own and operate the required furnaces and equipment, for what is rumored to be the screens for the forthcoming iPhone 6, but may turn out also to refer to Apple’s iWatch.

To find out more about sapphire glass — including its legendary toughness — Cult of Mac spoke with aerospace company Aero-Gear, who manufacture a sapphire crystal iPhone screen protector of their own. Below is what we learned from our conversation:

How Hard is Sapphire?

Hardness and durability is the main reason for Apple’s interest in sapphire glass. On the hardness scale, the only material tougher than sapphire is diamond. What this means is that it is immensely scratch resistant in a way that no other comparable material is — both in terms of “flaw initiation” (i.e. when it starts to scratch) and toughness (when it cracks). Its fracture toughness is around 4 times greater than that of Gorilla Glass.

To explore sapphire’s durability, the team at Aero-Gear put the glass through its paces, carrying out a series of tests to find the conditions under which it would scratch.

Their findings were impressive.

One test saw Aero-Gear drag a concrete cinderblock over an iPhone featuring a sapphire display. Amazingly, despite taking the entire weight of the block, and having its coarse surface dragged over the phone’s length, no visible damage can be seen.

Is Sapphire Heavier and Thicker Than Gorilla Glass?

From reducing the sizes of bezels on the iPad, to using a stronger glass to make its iPhone screens (meaning that you could have enhanced strength using a thinner piece of glass), Apple is always looking for ways to cut on the size of its products: with each new generation device ideally being thinner and lighter than the one that came before it.

In terms of direct comparisons, this proves problematic for sapphire — particularly when combined with the rumors that the iPhone 6 will feature a larger “phablet” screen. Sapphire is around 67 percent heavier than Gorilla Glass, with a density of 3.98 g/cm3 compared to the 2.54 g/cm3 used for Apple’s existing iOS devices.

In a blog post, Corning also points out that Apple may have difficulty achieving a comparable thinness should they opt to replace Gorilla Glass with sapphire altogether. While it may be true that sapphire glass is typically thicker than Gorilla Glass, Aero-Gear disputes that this is a significant issue: noting that its thinnest Gorilla Glass product carries an overall thickness of .55mm, including the bonding adhesive — compared to a comparative sapphire product, which has a thickness of .6mm (again, with bonding adhesive).The difference between these two is 0.05mm — roughly the equivalent of a human hair.

Concerns about thickness also ignores a recent Apple patent, which describes an alternative way of cutting wafer-thin sapphire pieces using an industrial laser.

Is Sapphire More Expensive Than Gorilla Glass?

Yes, it is. Manufacturing standard glass is a relatively cheap process. Gorilla Glass adds the cost of an additional chemical process to strengthen it further. Sapphire crystals, on the other hand, are made from minerals grown in furnaces. When the resulting material is removed from this, it’s not in the large sheets that glass emerges in, but rather in big blocks called “boules.”

The manufacturer then uses a diamond saw (or a laser, in Apple’s case) to slice the sapphire into the sizes they need for whatever product they are making at the time. The difficulty and slow speed of this process adds cost.

Even producing sapphire in the kind of quantities Apple will need to (especially if it opts to use it for iPhone, iPad or iWatch screens), the cost will still likely be around three to four times that of Gorilla Glass.

What Were Some of the Sapphire Glass Applications Before Apple?

As with the Corning Gorilla Glass currently used by Apple, sapphire crystal isn’t a new material.

The most likely interaction most people have with Sapphire crystal is in the displays used for the majority of high and mid-level watches. While glass was used by watchmakers for many years, sapphire is now used by many manufacturers since this better protects the watch against the elements. (Think about how much more exposed your watch is, compared to your iPhone, on a daily basis.)

Other commonplace uses of sapphire in everyday life include semiconductors and barcode sensors, where the material is again chosen due to its ruggedness.

Sapphire has also found widespread use in is the avionics world, where its ability to withstand extreme high and low temperatures — along with its resistance to damage — makes it a useful tool for the aviation displays in aircraft. Another regular application is in the optic heads of missiles. These missiles are regularly equipped with a combination of infrared, radar, and optical sensors for guidance, and the optic heads need to remain undamaged when the missile is moving through the air, or else being handled on the ground. Sapphire is also used in some iterations of bullet proof glass.

In Conclusion

Incredibly transparent as a material, and much stronger than Gorilla Glass, sapphire represents another way for Apple to differentiate itself from the pack — while also providing its customary high quality. The two main downsides of sapphire relate to both its heaviness and its price point. Through its innovative patents relating to cutting techniques, Apple is likely hoping to negate the former issue by reducing the thickness of its sapphire windows, although the resulting displays may still wind up being heavier than today’s Gorilla Glass screens.

As relates to price, sapphire is certainly more expensive for Apple to produce. Should the company opt to make future generation iPhone screens from sapphire, the cost of production will rise dramatically, although it’s not yet known how much (if any) of this cost Apple would try to absorb to avoid increasing the price point of individual iPhones.


About the author

Luke DormehlLuke Dormehl is a UK-based journalist and author, with a background working in documentary film for Channel 4 and the BBC. He is the author of The Formula: How Algorithms Solve All Our Problems, And Create More and The Apple Revolution, both published by Penguin/Random House. His tech writing has also appeared in Wired, Fast Company, Techmeme, and other publications. He'd like you a lot if you followed him on Twitter.

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