Arktos Crystal

[ettienne]

I had the crystal on my Arktos GMT AR coated at my eye doctor. Over time, the coating on the face of the crystal became scratched so I remove it with a brillo pad. After about six months, I noticed some fog on the crystal. When I disassembled it to clean it, I couldn't wipe off the fog. I used a cloth and then a dremel to lightly polish the crystal which I believed was sapphire(purchased from Eddie Lee) I popped out the crystal and it shattered in my hands. Upon a closer inspection I realized that it is not one solid crystal but two, glued together. The outside of each crystal doesn't scratch, like sapphire, but the inside, the sides that are glued together scratch like plexi-glass. I thought crystals were one solid piece. Is this the case with all of our supposed true sapphire crystals?

[sssurfer]

That was the so-called 'sandwich crystal', there have already been a few post about it.

Not all the sapphire crystals are that way, rather quite a few: most Submersibles, the $108 PAM 104 from Josh, and a few others.

The inside layer is mineral glass (I never heard of plexi inside, it could even be though).

It is that way because of the need to make a hole in it in order to get the socket for the cyclops (the so called "recessed cyclops").

This all is aimed to get a longer rehaut between the dial and the cyclops, so to get a better magnification and more room to the hands too.

Personally, I find it a genius touch. A thin sapphire layer is less expensive than a thick sapphire crystal but it provides the same scratch resistance where this is needed, i.e. on the outside of the crystal. And recessing the cyclops allows using a cyclops with higher ROC i.e. lesser cushion distortion.

I just wonder why not all the rep makers make it that way.

Maybe because the refraction index of the glue between the two layers is a very critical factor to prevent the occurrence of Newton rings, as sapphire and glass have quite different refraction indices.

So maybe that that glue needed peer research and design, and it is now sort of a secret by the maker who originally made it.

The only problem with those sandwich crystal is that you cannot have them AR coated with the high-temperature treatment as it would make the glue melt. Not a great issue, as the very presence of a cyclops already prevents that treatment.

Your eye doctor must have used the low-temperature treatment (that also gives explaination for the subsequent scratches).

[Watchmeister]

As always Sssurfer is right. And it is definitely mineral glass not sapphire or plexi on the inner side.

[alant]

Gosh looks like someone has the same issue as me! Recently, I bought a Cartier Santos 100 for my other half. Then one fine day, she told me that certain part of the front glass like 'blur'. I took a closer look, it doesn't look like scratches. I cleaned that 'blur' portion by rubbing it with those soft watch cloth. And magically the 'blur' part disappears! But after two days, the same problem came back again and exactly at the same spot! This really puzzled me. And same thing, I cleaned/rubbed that area with the cloth and all is ok again. This goes on and off and for a few times over the past two weeks. And I think the rubbing action generates some heat thus the 'vapor' disappears...and so 'blur' part also gone...

I begin to think hard and think it could be due to some tiny vapor being trapped between two pieces of glass being sandwiched together. So sort of just like the case over here. Oh man what should I do?

[sssurfer]

@ alant

Uhm, this makes me very dubious... As the Santos has no cyclops, I see no point in putting a sandwich crystal on it... Still, your guess is legit... Uhm...

Another possible guess is that the crystal is single-layer, and the vapor is inclined to condense always in that same point because of some small unevenness of the inner surface (quite unlikely, I admit).

Your simplest solution is removing the crystal and looking at its side with a loupe, it will be easy to tell whether it is single-layer or double-layer.

If it is single-layer, then your problem is "just" vapor in the watch.

If it is double-layer, you may either simply replace it, or try to get rid of any vapor entrapped between the two layers by gently heating it with a hairdryer (gently, not to damage the glue).

Best wishes, let us know how this comes out.

[alant]

Thanks for your analysis sssurfer. I guess you may be right. Its not one of those super reps and its not with sapphire glass no date cyclops as per mentioned by you so don't think its using those sandwiched glasses. I tried to remove the screws on the front of the bezel but like no use as I think those screws are for cosmetic purpose only. So guess have to remove the case back... What puzzles me is that the 'blur' part always occur at the same spot. Can vapor always be present at just one spot? After some rubbing it goes off and after a few hours or few days it came back again...tough luck...guess I must be those 1 out of a few hundreds...

[DuDro]

The "sandwich crystal" is also found on the PAM087. I had the "inside" of the crystal coated with AR that resulted in a minimal reduction in glare.

Since the bottom layer with the cyclops is mineral and the top layer is sapphire, would it be possible to separate the two and have the sapphire layer coated on both sides and heat treated, and then glue the two layers back together?

sssurfer...any comments on this?

Does anyone know where these crystals or separate layers can be sourced? I'm willing to conduct this experiment, but I don't want to lose the one and only crystal for my PAM087...

[yellomen]

thanx for the info guys... i was completely unaware of thise double layered crystals!