Sapphire Crystal vs. Glass

[FatMax]

I see people in most discussions here explaining the sapphire models with glass - when in fact Apples website states that it's sapphire crystal. I also remember reading the New Yorker interview at which one of the designers corrected a demo person after the Watch event that it is in fact crystal.

Could someone with the knowledge explain the difference to a mortal?

 

[JayLenochiniMac]

Could someone with the knowledge explain the difference to a mortal?

Yes, the designer was trying to be a know-it-all.

Well, there's a technical difference but he came across as having a superior air about him anyway.

 

[Knowimagination]

I see people in most discussions here explaining the sapphire models with glass - when in fact Apples website states that it's sapphire crystal. I also remember reading the New Yorker interview at which one of the designers corrected a demo person after the Watch event that it is in fact crystal.

Could someone with the knowledge explain the difference to a mortal?

The sport model has a glass screen. The apple watch and the edition models have sapphire screens.

 

[swordfish5736]

The cover on a traditional watch is referred to as the crystal, even if it's made of plastic or glass.

http://www.zales.com/jewelry101/index.jsp?page=watches_Crystals

 

[FatMax]

The cover on a traditional watch is referred to as the crystal, even if it's made of plastic or glass.

http://www.zales.com/jewelry101/index.jsp?page=watches_Crystals

Very interesting. Thank you for the info!

 

[Lennyvalentin]

Could someone with the knowledge explain the difference to a mortal?

What difference - between sapphire crystal and (crystal) glass?

On the atomic level, glass is always inherently non-crystalline, even if called just that. Glass is an anamorphic material, meaning the various atoms making it up are just jumbled together randomly, in no particular order or structure. This is just as true for crystal glass, which has traditionally and historically been called that due to its great optical properties.

A truly crystalline material such as sapphire, has its atoms arranged in a rigid, three-dimensional, grid-like lattice with a precise structure. It is the structure which gives the material its properties - carbon for example can be coal; IE, have no particular structure, or be graphite; hexagonal sheets of carbon atoms stacked loosely on top of each other. Or it can be diamond, with atoms arranged in a (had to look this up, lol) hexoctahedral pattern; essentially a repeating structure of cubes with a second cube set inside the first, rotated so that each corner sits at the middle of each face of the outer cube.


Okay, none of this was probably an answer to the question you asked, in which case...disregard. Lol.

 

[Foggydog]

What difference - between sapphire crystal and (crystal) glass?

On the atomic level, glass is always inherently non-crystalline, even if called just that. Glass is an anamorphic material, meaning the various atoms making it up are just jumbled together randomly, in no particular order or structure. This is just as true for crystal glass, which has traditionally and historically been called that due to its great optical properties.

A truly crystalline material such as sapphire, has its atoms arranged in a rigid, three-dimensional, grid-like lattice with a precise structure. It is the structure which gives the material its properties - carbon for example can be coal; IE, have no particular structure, or be graphite; hexagonal sheets of carbon atoms stacked loosely on top of each other. Or it can be diamond, with atoms arranged in a (had to look this up, lol) hexoctahedral pattern; essentially a repeating structure of cubes with a second cube set inside the first, rotated so that each corner sits at the middle of each face of the outer cube.


Okay, none of this was probably an answer to the question you asked, in which case...disregard. Lol.

I really enjoyed reading this. I learned something new today even though I probably will never remember how to spell or pronounce ( HEXOCTAHEDRAL).

Try saying that three times quickly.

 

[Deanster]

As noted above, for watches the crystal is what the clear cover over the face is called. Common materials for watch crystals are acrylic/plastic, mineral glass and artificial sapphire.

Acrylic is light and cheap and reasonably strong, tends to bend instead of breaking, and when it does break, does so relatively cleanly. Watches cleared for flight by NASA historically have acrylic faces, as glass/sapphire often creates tiny fragments when it breaks, which could be very dangerous if inhaled in a zero-G environment. The big downside of acrylic is that it's very soft, and scratches easily. You can polish out small scratches, but large ones are there until you replace the crystal.

Mineral glass is a very common crystal in cheaper watches - it's reasonably tough, resists scratches much better than plastic/acrylic, and it's fairly light and cheap. It's actually less-brittle than sapphire, but much more easily scratched, creating a bit of an odd juxtaposition where it's likely to scratch but not chip. Gorilla Glass, and whatever the Ion-exchange glass in the Apple watch is are much-upgraded versions of traditional mineral glass - the technology has come a LONG way in the last 10 years.

Sapphire is the penultimate material for scratch resistance (after only diamond). However, nothing in materials science is free, so the cost of that hardness is that it's considerably more-brittle than mineral glass, so all things equal, it's more prone to chips and shattering. Naturally, it's heavy, expensive and hard to work with. Since it's the next-hardest material after diamond, it can only be cut and polished with diamond-coated tools.

 

[Mikes1]

I'm curious as to weather anyone has experience of a synthetic sapphire watch crystal actually shattering?

 

[Night Spring]

I'm curious as to weather anyone has experience of a synthetic sapphire watch crystal actually shattering?

I googled "sapphire shatter" and found this

 

[Deanster]

It's relatively common, and it's a bit of a nightmare for mechanical watches, as all the little sapphire bits need to be cleaned out of the movement.

One guy on a watch forum notes that he's broken *five* sapphire crystals, but never a mineral glass one.

here's some examples, not all of the photos are on point, but enough to give you an idea:

https://www.google.com/search?q=watch+sapphire+chip
https://www.google.com/search?q=watch+sapphire+crack

FWIW, I own a dozen or so watches with sapphire crystals, and several with mineral glass, but the only one that's ever broken was a mineral crystal Luminox I'd loaned to a friend - it got smashed between rocks on a boulder sea-wall when he fell climbing around on it. I assume that level of impact would have destroyed pretty much any watch crystal, regardless of material.

He very kindly sent it into their service department and paid for the upgrade to a sapphire crystal as part of the replacement.

 

[Asthmatic Kitty]

Is there any difference in the transparency between ion-x glass and sapphire crystal? seem to remember reading something about sapphire crystal being less transparent (maybe from the gorilla glass guys when it was rumoured for iphone 6) - will this have any noticeable effect between the various collections of apple watch?

also, is anyone concerned that the composite back on the sport model might give less accurate HR readings than the sapphire back of the SS/edition?

 

[Julien]

Is there any difference in the transparency between ion-x glass and sapphire crystal? seem to remember reading something about sapphire crystal being less transparent (maybe from the gorilla glass guys when it was rumoured for iphone 6) - will this have any noticeable effect between the various collections of apple watch?

also, is anyone concerned that the composite back on the sport model might give less accurate HR readings than the sapphire back of the SS/edition?

Ever so slightly, but unless you have a stack of crystals you can't really tell. Sapphire tends to color shift to yellow. Glass color shifts too, just to a more eye friendly tent. As an experiment I will let you see for yourself what glass color shift is.

Experiment: Under bright natural light hold a pure white wash cloth 3' (1 meter) from of a mirror and notice the reflection looks the same white (optical illusion). Now move the cloth next to the mirror and notice the tent of the reflection. It is no longer pure white like the cloth and you can see the color shift without your brain fooling you. This is what glass does.


EDIT: Also as for the backs. They are the same sensors and will work the same. The SS and Edition simply have a ceramic coating added over the back to make it more durable.

 

[Lennyvalentin]

The SS and Edition simply have a ceramic coating added over the back to make it more durable.

It's the round sensor bump on the back which is ceramic (stated as zirconium by Ive in the introduction movie clip, with sapphire lens covers over the sensors); the rest of the back is either gold or stainless like the front and sides of the Watch.

Apple states the round sensor housing is "composite" on the sport model, but I'm unsure what sort of composite it could be. It looks very homogenous to the eye in the Apple-supplied web pictures, and not very 'composited' at all. *shrug* Maybe they mean the sensor housing is one type of plastic, with the lens covers another. Could be, but I doubt that really qualifies as a true composite...

 

[camtechman56]

Sapphire is a crystal while glass is melted and formed silica

 

[troop231]

I'm not sure it matters if it's sapphire or composite for the back if the sensors are facing your wrist, am I wrong? Why would durability matter in this case for the back of the watch?

 

[camtechman56]

I'm not sure it matters if it's sapphire or composite for the back if the sensors are facing your wrist, am I wrong? Why would durability matter in this case for the back of the watch?

I think they are interested in the difference between sapphire on the stainless as opposed to the glass on the aluminum models front display

 

[troop231]

I think they are interested in the difference between sapphire on the stainless as opposed to the glass on the aluminum models front display

I know, I'm just asking a new question about the difference for the back

 

[Piggie]

I know, I'm just asking a new question about the difference for the back

With most of these things, it's what someone thinks about it, rather than It, Itself that matters.

Plastic could be the most sort after material that everyone here would be desperate to have items made out of if things were a little different with what we can make.

 

[Asthmatic Kitty]

Here's what Apple says about the back of the watch on the website:

On the back of the case, a ceramic cover with sapphire lenses1 protects a specially designed sensor that uses infrared and visible-light LEDs and photodiodes to detect your heart rate.

1. Sport models have a composite back with hard coated optical polymer lenses.

Feel like the difference in the lenses could be significant in terms of accuracy - all the optical HR monitors in competing products have been pretty pants up to this point, so any little change could be significant to accuracy. Perhaps sapphire lenses are necessary to get a clearer signal, but it just wasn't cost-effective for the Sport?