# If sapphire glass is super tough why does it fail in this Gorilla Glass vs sapphire glass test? **URL:** \ **Category:** Factual Questions\ **Created:** [August 18, 2014, 7:21pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850 "2014-08-18T19:21:23Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [August 18, 2014, 7:21pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/1 "2014-08-18T19:21:23Z")
Obviously Corning Glass has a vested interest in promoting Gorilla Glass but Gorilla Glass taking 2.5 times a much downward force before breaking vs sapphire was a surprise after all the hype sapphire has received where it is supposed to be tougher and more scratch resistant. [Was this test legit](http://www.corninggorillaglass.com/gorilla-channel/Corning%C2%AE-Gorilla%C2%AE-Glass-vs.-Sapphire)or was Corning gaming it somehow? ---
**Author:** ![TimeWinder](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@TimeWinder](https://boards.straightdope.com/u/TimeWinder)\ **Post date:** [August 18, 2014, 7:26pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/2 "2014-08-18T19:26:52Z")
It’s probably legit. Sapphire is supposed to be more impact resistant and scratch proof; I’m pretty sure that it sacrifices flexibility for that (which on a phone or other display seems a reasonable tradeoff–how often do you bend your phone?) That said, I suspect most of the applications of sapphire are going to be layered with glass anyway: you get the scratch-'Proof’ness of the sapphire without all the cost. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 18, 2014, 8:04pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/3 "2014-08-18T20:04:30Z")
There are a lot of different measures of merit for a material. Hardness & toughness are not synonyms. Something can be very scratch-resistant but brittle. Natural diamonds are an example of that. So Corning picked a test which shows off the parameter where their product is better. The sapphire guys do the same showing off their better parameter. Which is better overall for the mission of a mobile phone case? Ask the guys who design them. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [August 18, 2014, 9:14pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/4 "2014-08-18T21:14:29Z")
Glass is quite strong in compression I understand. ---
**Author:** ![PorchePine](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@PorchePine](https://boards.straightdope.com/u/PorchePine)\ **Post date:** [August 18, 2014, 11:42pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/5 "2014-08-18T23:42:24Z")
Tensile strength, compression strength, flexural strength, shear strength, hardness, elasticity are all different measures of how “tough” a material is. Gorilla glass marketing has shown a test that they know they’ll win. That’s all that happened. ---
**Author:** ![DataX](https://avatars.discourse-cdn.com/v4/letter/d/e99b99/32.png) [@DataX](https://boards.straightdope.com/u/DataX)\ **Post date:** [August 18, 2014, 11:58pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/6 "2014-08-18T23:58:09Z")
Sapphire is extremely scratch resistant (you pretty much need a diamond or something else as hard as it is ruby/sapphire) - where the idea comes that it is shatter resistant is beyond me. Sapphire has been used for decades in nicer watches. As anyone who has dropped one of these nicer watches on a hard surface from a high enough height can attest - they WILL break. They will not scratch (under any normal conditions). In fact - the Omega Speedmaster - one of the only watches to make it to the moon - passed very rigorous tests by NASA - and beat out Rolex and others to be NASAs choice in space - has a sapphire crystal, but they bought a version made from hesalite - a type of plastic - over concerns about the sapphire crystal breaking. Even today - in the watch community - among those buying their first Speedmaster professional -the debate still rages as to which one is “better” - some like the vintage look of the hesalite and argue (rightfully) any scratches can be buffed out. Sapphire crystal is great - unless you drop it on a hard surface from a high enough height. ---
**Author:** ![Tabby\_Cat](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Tabby\_Cat](https://boards.straightdope.com/u/Tabby_Cat)\ **Post date:** [August 19, 2014, 1:23am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/7 "2014-08-19T01:23:53Z")
I’ve never shattered my iPhone screen before, but I have scratched them. I wonder if I would like this trade off, will I just not have any more scratches and nothing else, or would some “borderline” drops now result in a shattered screen… ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 19, 2014, 1:43am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/8 "2014-08-19T01:43:15Z")
> [@Tabby\_Cat](#): > > I’ve never shattered my iPhone screen before, but I have scratched them. I wonder if I would like this trade off, will I just not have any more scratches and nothing else, or would some “borderline” drops now result in a shattered screen… Gorilla glass gets it’s strength from being pre-stressesd, so any crack is guaranteed to become a whole-screen shatter. I suspect that Sapphire doesn’t need to be pre-stressed, so small cracks will remain small. We’ll see. ---
**Author:** ![Construct](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Construct](https://boards.straightdope.com/u/Construct)\ **Post date:** [August 19, 2014, 2:06am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/9 "2014-08-19T02:06:24Z")
Corning has a vested interest in promoting it’s own gorilla glass, which is currently the preeminent product for smartphone screens. This test is legit, in that if you recreate the testing conditions you’ll get the same result. But Corning chose a test that was going to look best for their product and worse for sapphire. For what it’s worth, no one’s proposing using pure sapphire like in the video anyway. Judging by prices for sapphire watch crystals, a piece of pure sapphire big enough for a phone screen and 1.0mm thick would run hundreds of dollars. Instead, all reasonable proposals use a very thin piece of sapphire bonded to a much thicker piece of glass. The sapphire provides scratch resistance (provided you don’t carry diamonds in your pocket) and the glass provides structural integrity. They already do this with watches and it brings the price down tremendously, so it could certainly work for phones as well. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 19, 2014, 1:16pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/10 "2014-08-19T13:16:08Z")
One other way that the video is subtly misleading is that they show the sapphire breaking, but not the gorilla glass. What they’re showing makes it seem like they ran their crushing-machine up to its absolute maximum, and the gorilla glass still hadn’t shattered, and who knows how much higher it’d be able to withstand if they had a stronger machine. I guarantee you, though, that they cranked up the machine all the way until it did break, and then cut the video short _just_ before that point so they could get the highest numbers possible. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [August 19, 2014, 2:00pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/11 "2014-08-19T14:00:22Z")
> [@beowulff](#): > > Gorilla glass gets it’s strength from being pre-stressesd, so any crack is guaranteed to become a whole-screen shatter. I suspect that Sapphire doesn’t need to be pre-stressed, so small cracks will remain small. We’ll see. I have a Nexus 4 with cracked Gorilla Glass. The crack covers the bottom right corner of the screen (about 10% of total surface area) and hasn’t spread since it appeared six months ago. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [August 19, 2014, 2:39pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/12 "2014-08-19T14:39:31Z")
> [@Construct](#): > > Corning has a vested interest in promoting it’s own gorilla glass, which is currently the preeminent product for smartphone screens. This test is legit, in that if you recreate the testing conditions you’ll get the same result. But Corning chose a test that was going to look best for their product and worse for sapphire. > > For what it’s worth, no one’s proposing using pure sapphire like in the video anyway. Judging by prices for sapphire watch crystals, a piece of pure sapphire big enough for a phone screen and 1.0mm thick would run hundreds of dollars. Instead, all reasonable proposals use a very thin piece of sapphire bonded to a much thicker piece of glass. The sapphire provides scratch resistance (provided you don’t carry diamonds in your pocket) and the glass provides structural integrity. They already do this with watches and it brings the price down tremendously, so it could certainly work for phones as well. [There are factory prototype iphone screens being shown on youtube](https://www.youtube.com/watch?v=5R0_FJ4r73s) that purport to be pure sapphire. No mention is made of these being a glass sapphire sandwich. Obviously the LCD itself may be glass but (so far as I have seen) the sapphire screens being shown are pure sapphire. ---
**Author:** ![PorchePine](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@PorchePine](https://boards.straightdope.com/u/PorchePine)\ **Post date:** [August 19, 2014, 5:01pm UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/13 "2014-08-19T17:01:24Z")
> [@astro](#): > > [There are factory prototype iphone screens being shown on youtube](https://www.youtube.com/watch?v=5R0_FJ4r73s) that purport to be pure sapphire. No mention is made of these being a glass sapphire sandwich. Obviously the LCD itself may be glass but (so far as I have seen) the sapphire screens being shown are pure sapphire. I didn’t see any claim that it was pure sapphire there, nor is it an official Apple video, so any claims aren’t those by Apple, but someone else. ---
**Author:** ![Construct](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Construct](https://boards.straightdope.com/u/Construct)\ **Post date:** [August 20, 2014, 1:07am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/14 "2014-08-20T01:07:26Z")
> [@astro](#): > > [There are factory prototype iphone screens being shown on youtube](https://www.youtube.com/watch?v=5R0_FJ4r73s) that purport to be pure sapphire. No mention is made of these being a glass sapphire sandwich. Obviously the LCD itself may be glass but (so far as I have seen) the sapphire screens being shown are pure sapphire. Nowhere in the video is the claim made that the screen is pure sapphire. What’s more, it couldn’t be pure sapphire at all. Sapphire has a Young’s modulus of [345-435](http://www.roditi.com/SingleCrystal/Sapphire/Properties.html) GPa as compared to glass, which has a modulus of [50-90](http://www.engineeringtoolbox.com/young-modulus-d_417.html) GPa. What this means in layman’s terms is that sapphire will be less flexible that glass along the axis of stress. The flexing shown in the video you link to could not probably not be achieved by a hardened, tempered glass without shattering; ergo, it can certainly not be pure sapphire. The screen show is likely sapphire bonded to glass or plastic, if not outright forgery. My guess is that the scratch test is faked and that the screen shown is polycarbonate, which has low optical distortion and is rigid but still flexible. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [August 20, 2014, 3:17am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/15 "2014-08-20T03:17:34Z")
Interesting - In looking around there is a “Is Apple using pure sapphire vs sapphire laminates” discussion here [Analyst Sees Pure Sapphire in Apple’s Upcoming iPhones](http://wallstcheatsheet.com/technology/analyst-sees-pure-sapphire-in-apples-upcoming-iphones.html/?a=viewall) ---
**Author:** ![get\_lives](https://avatars.discourse-cdn.com/v4/letter/g/ecb155/32.png) [@get\_lives](https://boards.straightdope.com/u/get_lives)\ **Post date:** [August 20, 2014, 3:27am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/16 "2014-08-20T03:27:39Z")
There’s no way they’re using pure sapphire screens in any phone this year. Their price points for iPhones have remained unchanged for at least the last 4 years, IIRC, and they would HAVE to change their price points on the iPhone 6 (from the introductory price points for each previous new model) in order to make a comparable profit on the iPhone 6, if they used pure sapphire instead of laminate. ---
**Author:** ![TimeWinder](https://avatars.discourse-cdn.com/v4/letter/t/bcef8e/32.png) [@TimeWinder](https://boards.straightdope.com/u/TimeWinder)\ **Post date:** [August 20, 2014, 3:30am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/17 "2014-08-20T03:30:27Z")
> [@get\_lives](#): > > There’s no way they’re using pure sapphire screens in any phone this year. Their price points for iPhones have remained unchanged for at least the last 4 years, IIRC, and they would HAVE to change their price points on the iPhone 6 (from the introductory price points for each previous new model) in order to make a comparable profit on the iPhone 6, if they used pure sapphire instead of laminate. We’ll know in three weeks or so, so it’s hardly worth the speculation, but I’ll be very surprised if the iPhone intro prices don’t go up, since they’re getting supposedly getting bigger, and because as you’ve said they’ve been steady for a long time. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [August 20, 2014, 4:01am UTC](https://boards.straightdope.com/t/if-sapphire-glass-is-super-tough-why-does-it-fail-in-this-gorilla-glass-vs-sapphire-glass-test/695850/18 "2014-08-20T04:01:30Z")
About two years ago we upgraded to Motorola Droid Razr Maxx, with Gorilla Glass. Segue to about two weeks after acquiring my new phone. I had just parked at work, with my phone, face up, sitting on the front seat next to me. I had a sharp pencil (real #2 wooden pencil) in my hand when I accidentally dropped it on the front seat next to me. I estimate the height of the drop at about nine inches. It struck the phone with the pencil point. Now where it struck the phone was critical; a small part of the glass that was open to expose the ear speaker. Right on the edge of the glass. A one in a million hit. The Gorilla Glass shattered. I was told later this is similar to the safety glass in those all glass shower stalls. You can bang on the glass plate all you want and the glass will remain intact (OK, let’s be reasonable). But strike the edge of the glass just right and the shower door will shatter. Just like Gorilla Glass.