About the Green Crystal in the Milgauss...

[Lol-x]

We look at our watches every day, but we rarely consider the origins of what we are looking through i.e. the sapphire crystal.

The sapphire crystal is an artificial (“synthetic”) man made material that is ‘grown’ over a period of days or weeks.

The growing process is even more complex in the case of the Green Milgauss Crystal.
Corundum is the mineralogical name for the naturally occurring crystalline form of aluminium oxide (sapphire).

The chemical formula for the Synthetic Green Sapphire is Co3+ - Al2O3. In other words synthetic green sapphire is made from Copper and Aluminium Oxide, the latter being the main product of bauxite the principal ore of aluminium.

The production of synthetic sapphire crystals can occur by one of several processes: melt growth, solution growth, or extremely high-temperature, high-pressure growth.

The 4 well known methods of sapphire production are:
1. The Verneuil flame-fusion process
2. The Bridgman-Stockbarge process
3. The Czochralski method
4. The Hydrothermal method

It is not precisely known which method Rolex uses to produce their sapphire crystals, but rumour has it that Rolex uses the Hydrothermal method of producing the green sapphire crystals.

The Hydrothermal method is based on the transformation of melting crashed sapphires and deposit of solution around the beryl seed in a hydrothermal environment. The crashed low grade sapphires, known as nutrient, are melted along with the color inducing chemicals (copper is used for obtaining a green tint). The seed, being a larger and more solid element in the process, attracts smaller particles of the same origin and the growth process begins, depositing layer upon layer on itself. This is the reason for undulated growth lines in hydrothermally grown gems. The process takes around four weeks. If the process is slowed down, the “layers” are deposited at a slower rate, resulting in growth lines being less defined and more difficult to detect.

The process starts by gradually heating the autoclave. Subsequent rise in temperature leads to rise in pressure, as a result of liquid expansion inside the inner vessel. Once the temperature rises to about 600°C and pressure is around 800 PSI, the process reaches an ultimate equilibrium and a melt process begins. Smaller particles are attracted by the larger element, the seed, hence starting the growth process.

http://tairus.com/index_files/emerald.htm

The hydrothermal synthetic sapphire 'growth' process is similar to Synthetic Emerald production process.


Synthetic sapphire ranks a 9 on the Mohs Scale, this means that one needs to avoid exposure to diamond jewellery, and avoid striking ones watches against artificial stone and simulated stone surfaces. Such surfaces can often contain materials including silicon carbide, which, like diamond, are harder than sapphire and thus capable of causing scratches.

The slow run out of the green crystal milgauss (and the higher cost than the clear crystal models) may well be explained by the complex process involved in the growth of the green crystals. The addition of copper to the process to obtain precisely the right amount of green tint, and the precise pressures and temperatures to yield a perfect product are liable to failures occurring in the ‘growth’ process.

[2careless]

Probably I'll get slammed hard on this... Why are people so adament about that green crystal? Drink some beer and you can see your watch looking green through the beer bottle...

[marshallr47]

Good info. Very interesting. Thanks for sharing.

[DaveInLA]

Personally, I think the Milgauss with the green rim is the best looking watch I've ever seen.

[Trurolexer]

Originally Posted by 2careless

Probably I'll get slammed hard on this... Why are people so adament about that green crystal? Drink some beer and you can see your watch looking green through the beer bottle...

That's what I'm thinking too, Kai. lol!!!
BTW nice info, Steve.

[mic6]

I heard that the green was not a plain coating on the crystal but natural ...who knows

[BiG JeEzY]

Thank you for sharing Steve! That was explained so well and was very educating!! I always am fascinated by Rolex Sapphire crystals and how they are cut so well, perfectly flat. It creates a shine that is very beautiful in my opinion.

[toph]

great info.

[docnagel]

Super explaination. Thank you!!

[youngr]

really enjoyed reading that thanks

[swatty]

Very interesting , Thanks

[Andad]

Hi Steve,


Excellent information.

I will now enjoy wearing my GV even more.

[Luminor]

all i know is this

[speicher1]

Great thread! Ok question. Is the green crystal purely aesthetic? Or does it have some practical purpose/advantage over the regular crystal?

[OYSTERMANN]

What a fascinating post, Steve - amazing information in there.

[unclesallie]

Steve: AMAZING. I had no idea.
Thanks!
best,
dan

[oneillba]

Steve, thanks for the information. I had no idea that the crystals were man made. I thought they were mined, cut and polished. You have given me my Bo fix for the day.

[Trainer]

Originally Posted by speicher1

Great thread!* Ok question.* Is the green crystal purely aesthetic?* Or does it have some practical purpose/advantage over the regular crystal?

Good Question!Does this crystal privide a greater resistancto the effects of magnetism?

Tempus Fugit,
Trainer

[Andad]

Oh, sorry Steve, did you want a few more pix.........?

[ROLEX MAN]

Thanks steve excellent!

[Lol-x]

The green crystal is purely an aesthetic feature of the Milgauss GV. The tint is very slight and can really only be observed on the edge of the crystal.
Thanks Eddie I love seeing your Milgauss GV, it is still the only GV I have ever seen in person
After the crystal has been grown, it must then be cut and finished to exacting standards and so this all adds to the cost and time to make this model.

[redshirt1957]

Usually you have to pay for that type of information. Very well written.

[Texsubmariner]

I just wish the Milgauss has a date function, then it would be a perfect watch!

[Lol-x]

Yes, if the Milgauss had a date it would be a very useful addition, but alas we do not dictate the terms

[Tools]

Great stuff..

This should be posted over in the Milgauss reference section too..

[docnagel]

Originally Posted by Texsubmariner

I just wish the Milgauss has a date function, then it would be a perfect watch!

But that would probably mean a cyclops which may detract from the Green tint in the crystal.

[Leighton]

Originally Posted by Texsubmariner

I just wish the Milgauss has a date function, then it would be a perfect watch!

x2!

Thanks Steve. Great info!

[Beef]

Thanks, Steve. Now I know why I'm still waiting.....

[kilroy]

[jasonbellevue]

Interesting info, thanks for sharing.