Horological Meandering

I just thought that I would throw this question open to the forum

Most of the pieces that I have owned in the past have not had their glass coated with AR.

And until now I have not given the matter much thought, but recently I was comparing my Patek 5205G which does not have AR to a Grand Seiko Hi Beat that does, and though I love wearing the Patek, one of it's disadvantages (for me) is that in certain light it can be quite difficult to see the time.

So when I compared reading the time of the Patek with the Grand Seiko, the advantage of AR became quite apparent to me.

Whether it made any difference, but the Patek has a dark dial while the Seiko was a lighter colour?

What are your thoughts, is AR glass an advantage or not?  

That gives legibility a huge jump.  Lange started applying ARC on their glass relatively recently and the early production of Lange did not have it.  I loved it when I replaced the Lange 1 MOP and the mysterious varying light and color on MOP dial became really beautiful.  There may be the time when ARC glass actually hurt the beauty of the dial, but I can't think of any for the momet.  I used to wear glasses on and when I changed my glasses to the one with ARC, the difference was night and day, so it must be good for watches when it comes to legibility.

Ken 

anti reflection 2 types, some watch manufacturers only apply AR on the inside of the sapphire to my knowledge, the speedmaster 3573.50 does this rendering the inside sapphire anti-reflective. Iwc pilot has it on both sides. Rolex does not have AR on their sapphire as far as i can see. I like anti reflective sapphire because when u look at the dial, it is almost transparent, i feel breitling does a good job on this on all their watches i think. Also for the same brand, AR sapphire on both sides may be priced higher too, i might be wrong. Watches with complicated dials should have AR on both sides of the sapphire to enable easier reading imo. This message has been edited by KCKL on 2011-02-24 16:04:23

I can't think of any disadvantage of AR coating, except cost, and maybe the possibility that AR coat on the outer surface of the crystal could be damaged over time. Some AR coats can also give a certain colored tint depending on angle/, lighting, but I have not really experienced this on watches.

Aesthetically I have always liked the look of AR coating, especially over dark colored dials. Most important is to have the AR coat on the outer surface. I have a watch with AR only on the inner surface of the crystal, and the beneficial effect is rather minimal.

I didn't realise that you could AR both sides of the crystal.

And that each side has it own merits, as I just assumed that if the glass had been coated with AR then it would have the same benefits for either side.

I suppose that if only the outside is coated and that could be worn off over a relative small period of time, this could be the main reason why many brands don't coat their glass.

...coating. Todate i have not seen any AR coating done on the outside only. Usually both sides or insides as to prevent the dial reflection from the inside. My 2 cents Topcat.

vacuum deposition are done at ~120 C.

When Peter Speake-Marin was touring his Thalassa with the SM2 movement last year he had one watch with AR coated sapphire and a second (which was finished at the last moment) without. It was very obvious to the naked eye (and the camera lens) how the movement and finishing just 'popped' and was much more impressive to view through the coated sapphire.

Remember also that the AR coating reduces, but does not eliminate, reflections. It absorbs most of the light spectrum but leaves the purple/blue reflections that are not as bright to our eyes - human eyes are less sensitive to blue colours. Note that there are some AR coatings that reflect green colours instead.

Andrew

AR Coatings on Watch Crystals
An Explanation and FAQ’s

AR coatings are designed to reduce light reflection (increase transmission) by optical interference. The principal is the same as in noise canceling headphones. The AR coatings bend the incoming light wavelengths and eventually one wavelength cancels out another. Generally, reflection is reduced to < .5% per side and transmission is therefore increased to over + 99% depending on the substrate and its thickness. Uncoated, clear glass (2mm) reflects 8% and transmits ~91% (the difference is absorption).
The AR layers are nanometer (billionth of a meter) thick layers of a metal oxide material. The materials my include titanium or zirconium oxides individually or in combination. The outside layer is silicon dioxide. The multiple layers, from three up to 20 or more, are on both sides of the substrate. Typically, there are at least six total layers; three on each side of the crystal. The coatings are applied most often in a vacuum deposition system. Targets of the metal oxide are vaporized in a vacuum chamber with high energy and in the vacuum are attracted to the crystal of an opposite electrical charge and bond to the crystal surface in a very thin and uniform thickness. The layers each have a different index of refraction and hence bend the light differently creating the optical interference, canceling of reflected light.
What is the major benefit of AR coated crystals? In my opinion, the major benefit of an AR coating is increased light transmission. With more ambient light striking the dial, the more color and texture you are able to see. The side benefit is reduced reflection that, if not reduced, is annoying.
Why is there a bluish color of reflection with AR coated crystals? It is a color chosen by the optical engineers to be less garish than, let’s say, red. The thickness of the layers determines the color of reflection. Optical engineers can design the optical system to reflect any color, but blue is often chosen as being less intense and its complimentary color of transmission being a light orange /yellow which is less noticeable and intrusive. The coatings on watch crystals transmit a light yellow (kind of like incandescent light) because its complementary blue color is being reflected / taken out of the visible color. You could have a violet / red color of reflection and a slight greenish color of transmission, but that would be a not be a great system for a watch crystal.

Why do I sometimes see a different color transmitted onto the watch dial? At an angle the color and intensity of the reflected light shifts slightly to violet at an angle and the color of transmission changes with it. In addition, the color of the ambient light affects what you see. Daylight has a much different Kelvin temp than incandescent for fluorescent light and that too affects what is reflected from and transmitted to the dial.
Why do I see more reflected light at an angle? AR coatings are angle dependent. The maximum reduction in reflected light is at 90 degree viewing angle. At an acute viewing angle, the % R increases.
Why coat both sides of the crystal? Coating only one side of the substrate is half as effective as coating both sides. If you only coated the backside of the crystal next to the dial, you would get ~ 4% reflection off the front side plus ~ .5% on the backside. The total reflection would be high at +4.5% vs. the goal of < 1% total reflection. Two sided coatings are, therefore, optimal for minimal reflection and to obtain maximum light transmission onto the watch dial. The small negative is that the AR coatings are softer than the crystal itself and can scratch. But with care this can be minimized. It is cheaper to replace the whole crystal than to have an existing one recoated.
I am not an optical physicist or scientist so this is a laymen’s explanation of how AR systems work. I was on the Management, Sales and Marketing side of a AR coating company. I hope this is helpful and if there is an error in my explanation, I trust it will be corrected by those more knowledgeable.

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esp on black dial. The crystal just seems to disappear at certain light/angle and the purple glare is nice too.

Best,

Goh

Which has helped me understand more about the complexities of ARC.

I feel that it is certainly an advantage to have it fitted to a timepiece.

Perhaps it would be something that Patek and other brands may decide to do in the future................Here's hoping

Advantage: Easy to read.
Disadvantage: Easy to wear off.

Serious problem of AR coating is that all of them are fluorine-coated.
Thus durability of these coating is very and still poor.


Two or three years before, I`m not sure exactly, CITIZEN developed TOUGH AR coating.
The Result is marvelous, but they still keep secret about coating process.

If I can say my personal opinion, One surface coating is the best considering durability.
It`s not difficult to distinguish whether coated both side or one side.
If colour of Glass seems yellow or blue, it may have one surface coating.


Regards,

HIROTA, Masayuki

I would not buy a watch which has AR on both sides because when the AR rubs off, it doesn't rub off evenly so there will be a really ugly uneven rainbow hue to it at a certain angle. I think there is a picture somewhere of a Porsche Design watch having that effect. It really is a bad idea to put something that rubs off so easily on something so scratch resistant.

So AR on both sides is really a bad idea. If I'm not mistaken, Omega Seamaster has 1-sided (inner) AR whereas the newer Planet Ocean has double-sided AR. My Rolex Sub does not have AR and I have no trouble with reading the time. The only trouble I have is with the date cyclops, hence the latest Sub has AR on the underside of the cyclops and this really makes a difference. I guess Rolex has given this thing more thought than Omega. To fix it you need to change the sapphire and the Omega ones are significantly more expensive that Rolex's!

Moral of the story - beware of double-sided AR. It will most likely reduce the beauty of your watch in the long run.

Yes AR coatings are softer than the underlying crystal, but unless you are using sandpaper to clean your crystal, the coatings if properly applied are durable. I am not particularly cautious with any of my AR coated watches and none have damage. By choosing to go only with one side coated crystals, you lose 50% of the positive benefits clarity in viewing the dial and the reduction in reflection. Some manufactures are using inferior and cheaper coating techniques at a cost to performance. I would not lump all manufactures in the same boat and degrade the real advantages of AR coatings. This, obviously, is my personal opinion.