"Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

Thread: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

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  1. #1
    Member cnmark's Avatar
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    "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    To answer the question first - in my opinion the answer is yes. Read on...

    After reading lots of posts on the Sinn forum about removing the outer AR (anti reflective) coating from the crystal due to visible scratches, here some thoughts about the advertising nonsense of a "hardened" AR coating.

    AR coatings are used to increase the readability of the watch dial under oblique angles, an optical good AR coating can even make the crystal invisible under certain view angles. But - as many of us know from bad experience - the gain in readability is bought by a gain in scratchability.

    Some watch companies advertise now that the AR coating on the crystal is "hardened" (e.g. Sinn and Mido). Hardness values of "1800 Vickers" are advertised. Impressive high numbers, but for measuring the scratch resistance these values are unfortunately nearly useless. The Vickers hardness or other quantified metallurgical hardness tests (Brinell, Rockwell, Knoop) test the resistance against deformation by static penetration. We all know that a scratch does not result from an action that can be described as static penetration.

    Actually there is no quantified test or scale for scratch resistance, apart from the Mohs hardness scale dating back to 1822 and used by mineralogists to determine the relative hardness of minerals by scratching. Using the Mohs scale, mineral glass has a relative hardness of about 5.5 to 6, sapphire has a relative hardness of 9 (Diamond is hardest at 10).

    An AR coating on a sapphire crystal consists of multiple very thin layers of rare earth metal salts, applied in a process similar to PVD (to keep it simple). These materials do have Mohs hardnesses in the range of 6 (rarely 7). Thus the scratch resistance of an AR coated sapphire is basically back down to the scratch resistance of mineral glass. Regardless what impressive "Vickers hardness" the AR coating might have.

  2. #2
    Member Peter Atwood's Avatar
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    I agree. I was terribly disappointed to find that my Damasko DA-36 was very easily scratched and now has about 5 tiny hairlines in the AR coating. Now my U1 has a small one that I just discovered last night. In the real world all those hardness numbers don't mean diddly.
    Rotating on my wrist this month: Stowa Blue WatchTime Flieger, Sinn EZM9, Sinn T1, Sinn 556 Blue, Stowa Antea LE Polish Forums, Stowa Verus 40, Damasko DS30 greenie, Sinn U1, Stowa Antea Klassik KS Rose, Nomos Tangente Silvercut





  3. #3
    Member particleman's Avatar
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    Thanks for the info Cnmark! I was just wandering about this. Are their any companies that put the ar coating on the inside face of the crystal? Would that improve readability?

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  5. #4
    Member cnmark's Avatar
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    Quote Originally Posted by particleman View Post
    Thanks for the info Cnmark! I was just wandering about this. Are their any companies that put the ar coating on the inside face of the crystal? Would that improve readability?
    Companies with "double sided" AR coating (can remove the outer coating like so many Sinners):

    Fortis
    Sinn
    Mido

    Others for sure also...

    The double sided AR coating is optically only necessary for camera lenses (avoiding "lens flare"). On watches the second (outer) AR coating does only marginally improve the readability over single (inner) coating, at extreme viewing angles.
    The glasses I wear have single sided coating only - pretty scratchy...

  6. #5
    stuffler,mike
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    I am very pleased with my DC 56 and double AR coating. As some of you know I used the watch whilst mountain climbing and I appreciate to read the watch in a glance, regardless of the sunset. And to add that: No scratches since I own this watch.

  7. #6
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    I've got a Sinn U2 with an outstanding super hard a/r coating. Almost 15 months of hard ownership hasn't phased it at all. No scratches, no wear, very little, almost inconsequential smudging, and easy cleaning. Couldn't ask for better actually. It was and is as advertised.

    I also have a Sinn UX which has a not so good outer a/r coating. It has a hairline scratch in it already and it hasn't had 1/10th the usage and definitely no hard usage. It smudges very easily and is super hard to clean off.

    The concensus over on the Sinn forum is that there are several companies which are applying the a/r coatings on the sapphire. At first, we believe, when the demand wasn't exceeding their ability to provide, the a/r coatings were great but as Sinn might have panicked with the meteoric rise in interest and subsequent explosion of names on waiting lists and farmed out the application to other companies, quality control may have went out the window.

    Either way, you will never know what your gonna get when you order a Sinn with a super hard a/r coating. And that's just terrible. This should never be and we are all hoping that Sinn is reading the threads at the Sinn forum because we let 'er fly there and won't censor ownership experiences from our members. Hopefully, Sinn has addressed these concerns and have made the necessary moves to fix this. But for now, I believe it's unacceptable. Especially when you consider the ridiculous overengineering and super high build quality of their wares.

    As for the other companies which employ similar a/r coatings, I have no knowledge of similar problems. Considering the fact that there is an apparent multi company problem with this maybe the outer a/r thing is something to be left off if the companies can't deliver on their promises.

    I really don't think the outer a/r coating is necessary anyways and the removal of such or at least the option to buy without should be given.

    Just my thoughts on this.

  8. #7
    Member cnmark's Avatar
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    Now, let's see what brands and experiences do we have up to now:

    A Sinner with a scratch-free watch and a watch with scratched coating (plus all the posts in the Sinn forum).
    A Damasko with scratches and another Damasko without. I do know of a Mido with scratches.
    Regarding Fortis, from own experience: I own two without scratches, the Marinemaster is worn under worst conditions. Up to last week I believed Fortis was not affected, but then I've seen one watch that was already slightly scratched from store handling only. On the scratched one the color cast caused by the AR coating was also slightly different than on others Fortis I have handled so far.

    Any other brands?

    I agree with Patrick that is a problem of the suppliers and the in-house QC. Fact is that in phases of high demand a manufacturer might get an additional supplier in that can not meet the standards, or the standards are just not controlled. For cost reasons a supplier might be changed. Outsourcing also has to do with economics, so regarding hardness you might only get what the watch manufacturer paid for...
    Last edited by cnmark; March 27th, 2007 at 16:51.

  9. #8

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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    well theres this one thats been pretty good so far......



    Haven't had a problem out of either.

  10. #9
    Member Dieselweasel's Avatar
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    Quote Originally Posted by cnmark View Post
    Now, let's see what brands and experiences do we have up to now: [...]
    Any other brands?
    Sinn UX and Omega Seamaster Planet Ocean - no scratches so far.
    But my Omega Speedy with Hesalite has also no scratches. It might be that due to I'm an office guy my watches are less "stressed".
    For rough usage I prefer to wear my Stowa Seatime without coating.

    Cheers, Ralf
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    Glashuette Original Senator Kalenderwoche - Nomos Orion - Omega Railmaster - Omega SMP GMT

  11. #10
    Breitling Forum Moderator SnapIT's Avatar
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    Re: "Hardened" AR coatings on sapphire crystals - Pure advertising nonsense?

    Interesting thread.

    The grading of AR coatings, from civilian to military to medical to astronomical to horological to aviation to personal ocular covers many many formulations and deposition methods. I think a watch maker could easily under spec or off spec what they think will do the job and have delivered a finished component that doesn't match the end user expectations. I grant that the application of AR coatings should have industry "norms" that have proven them selves. From the little research I've done its evident that with such a broad spectrum of product to select from its too likely a wrong spec could be ordered. The inconsistent performance of certain lenses I think reflects this[no pun intended]. Even the fact that the multiple coatings are heat treated to cure for hardness between coats and that is controlled by exposure time at certain temperatures rolls in a wide spectrum of possible finished coating characteristics.

    Check it out... from the guys who know a thing or two

    Last edited by SnapIT; March 27th, 2007 at 09:41.
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