A. Lange & Söhne

THE LANGE MOON PHASE MOONDISC


Recently I discovered how these wonderful moondiscs are made but this process has been around since ~2005 at Lange.

If you hold up to the light a Langematic perpetual up close and gazed intently at the moonphase. There is clarity, there is depth, there is a blue shimmer on the background that brings out the best in the floating stars and polished precious metal moon. (The entire moondisc itself is made of gold)


Large Model of the Langematic Perpetual Movement







Traditionally on very old clocks, the rotating moonphase itself was usually a brass disc. The stars and moon were pieces of gold shaped and hammered into the disc using an inlay technique that was known since thousands of years ago. The blue night sky were painted on and layers and then a thick coat of clear lacquered added to give the moondisc this look of depth. Sometimes the clockmaker would add some very fine gold dust in to the lacquer layer to give the depth of the moondisc a touch of shimmer and glitter.








Lange achieve this same depth and shimmer effect with a very different approach to the manufacture. State of the Art Tradition is realized in the Lange moondisc by using very modern cutting edge process to achieve the same visual results as the old masters. This is truly the epitome of the Lange mantra and the technical precision and method employed is very impressive for the manufacture of a single small moondisc disc alone.



The exact method use is known as "pulsed arc deposition" in engineering circles and this leaves a super hard amorphous carbon film on the gold moonphase disc. The process was first described in a Materials & Science Engineering journal published in 2004 and the authors were from a Nano Materials & Beam Research Institute in Germany.

Carbon films are characterized by their broad structural variability and can form substances like soft graphite to hard diamond. The blue background you see on the Lange moondisc is actually deposited carbon and it appears blue (why blue? it will be explained later).


Schematic of Pulsed Arc Deposition
*ta-C film=superhard tetrahedral amorphous carbon film



The blue carbon coating on the moondisc is very similar to a DLC (diamond like carbon) process that is carried out in a vacuum chamber. The vacuum is typically 10 to power -4 Pa and the plasma is produced by arc erosion of the target material (cathode) which is graphite-based in this case.

So what is the main difference between DLC and "pulsed arc deposition"?
DLC is a plasma enhanced CVD (Chemical Vapor Deposition) process and is used is used for the deposition of DLC resulting in a considerable amount of hydrogen content. Pulsed arc deposition is different and is based on a pulsed arc controlled by a laser. The resulting coatings are free of hydrogen and show superior properties as compared to conventional DLC coatings. The hardness typically is even higher by a factor up to three and the coefficient of friction can be considerably reduced further.

The pulsed arc deposition process control is carried out using a Nd-YAG laser that is Q-switched an has a power of >5x10 to power 8 Watts per cm2. That is a lot of energy density!! The laser is then focused on the graphite target material and it produces a small plasma cloud that ignites in the vacuum arc. The laser is typically pulse length is about 100 nanoseconds and is two to three orders of magnitude smaller than the arc pulses themselves.

The pulsed arc plasma containing the vaporized carbon is then deposited on the substrate (the gold moondisc itself). The energy used allows arc currents of up to 1500 Amps and a pulse repetition frequency of up to 1000Hz. Fraunhofer institute has commercially implemented this process and it is registered trademark name with applications for large scale industrial coating processes.

Dial side of the Datograph Perpetual Movement Showing the Moondisc



Basically, a pulsed laser triggers an electrical arc discharge that liberates material from a rotating carbon drum to be deposited on the gold moondisc. In order to look uniformly blue to the human eye, the controlled layer being deposited on the disc must ultimately have the same thickness throughout.

The blue shimmer on the gold moondisc is deposited carbon layer but how can relatively colorless material be made to appear deep blue?
Here is the Pièce de résistance of the blue shimmer. The secret is in the control of the thickness of the deposited layer down to micron precision. Light is reflected internally from the top and bottom edges of the deposited layer and the phenomenon interference causes all wavelengths to cancel each other out – with the exception of blue in this case. The process can can easily create other colors by changing the thickness of the coating film but I very much doubt we will see a green moondisc anytime soon.

Although the "blued" moondisc sits comfortably behind a protective sapphire glass, the blue film on the gold moondisc is the material is actually ultra-hard and extremely wear and scratch-resistant armophous carbon deposit. A similar process is used in the automotive industry to coat the contact surfaces of an engine's camshaft to increase greatly wear resistance in high performance and racing engines. The ultimate use of this coating technology is as a coating in an implantable mechanical heart for human use (The Ventracor LVAD - the cardiothracic boys here will grin).




Lange have saved the best for last and you might now wonder how the shiny stars and are applied to the moondisc - The answer is that they are not applied! The gold stars are the original moondisc gold material themselves. This is done by directing another laser beam at the coated disk through a mask. The beam removes the coating in the exposed areas only. The structures are uniformly recessed and brilliant golden stars appear.

The finished Lange dial is stunning multilayer with the moon rising out as a polished convex, then the depth of the blue shimmer produced by interference of light from the carbon deposition and finally the recessed tiny brilliant golden stars.







This same coating was also used in the Grand Lange 1 Lunar Mundi series of unforgettable masterpicees from Lange. The pair of watches were issued in a limited edition of 101 sets and the moondiscs were white gold and rose gold to which the process was applied.

This certainly has to be State of the the Art Tradition at its finest hour - the Lange moonphase shines more brightly than ever in the cosmos of the collector mind's and....BTW should I also mention that once the moonphase is correctly set, it will move continuously for 122.6 years before the aggregate error relative to the synodic lunar orbit amounts to one full day. Langematic owners will now pay more close attention to the seemingly ordinarily blue moon phase of their watches in light of this (no pun intended :-P)


Lange 1 Movement with the Moondisc















Over the moon, hope you enjoyed the read.

PS: I do apologize for the photos that do not do justice to the watches. In real life they are incredibly stunning

so the "blue" carbon layer is removed with a laser; but looking at the first picture you posted:



it seems to me that the two moons present on the disc are 3D in appearance and not "flat" ... does the
laser not only remove the carbon but also a little bit of the gold moondisc underneath?

Edwin

but i presume that the process begins with not applying the "blue" ta-C layer to where the moon positions are to start with. the moons are concave and polished and they probably leave this alone from the start. the process can be controlled very accurately and its easy to not 'blue' the moons from the start.

as for the stars, they are produced by removal using the 2nd laser and hence they are sunken into the 'blue' layer.

so they start with the gold disc where the concave (arent they convex?) moon(s) already present?

and how do we discriminate the old moonphase discs from the new?

Edwin

of which the answer i know not of

light waves reflected at the gold substrate and light waves reflected at the "blue" carbon will cancel out each other - the color at which this happens is depending on the thickness of the carbon deposited on the gold disc

Thanks

E

It is what happen on camera len as well, so you can captured you lange well...^_^
This message has been edited by Ogygia on 2009-06-25 10:19:50

No message body

When the platinum Langematik Perpetual was introduced, it had a very dull, dark blue moonphase disc. It was my only complaint about that watch. A few years later, Lange change the blue color to the current, lighter, more vibrant blue. About a year or two ago, I had the moonphase disc change from the old one to the newer one, and IMHO the watch is much more pleasing to the eye now. I wonder if there were major differences in how the old vs. the new were manufactured.

This was a GREAT post -- very informative! -- thanks for making it.

Much appreciated!

Stephen

This reminds me of the  vacuum deposition process to put down the nanometer thick metal oxide layers for AR coatings on crystals. 

Bill

very informative
Cheers

nt

No message body

Looks like a complex process with plenty of room for error, defects, and rejections that complicate the process.

No message body