Vacheron Constantin

Skeletonizing at its most basic is, according to The Illustrated Professional Dictionary of Horology, taking a watch and rendering the case and various parts of the movement transparent, enabling the underlying parts to be seen.  Frankly, this seems a woeful description for the astonishing levels to which haute horlogerie has taken the art of skeletonizing.

The Foundation de la Haute Horlogerie informs us the concept sprang from the mind of André Charles Caron sometime between 1720 and 1760 when this Parisian horologist, also renowned as clockmaker to Louis XV and master of Jean-Antoine Lépine, first pierced the bridges and plates of his watches to allow a view of the mechanical motion occurring beneath.

In one of the earliest articles found at The Hour Lounge, Alex Ghobti narrated the story of skeletonizing, or "openwork" as they've dubbed it, at Vacheron Constantin circa 2007:

"Skeletonizing a watch movement into a piece of scintillating metal tracery demands exceptional deftness and precision, generating considerable added value in the process.  Scrupulous observation of a series of mandatory steps is vital to the successful production of that delicate combination of airy transparency and delicate lacework that mark Vacheron Constantin's skeleton pieces.

The process begins with the drilling of holes in the bridges, bars and mainplate on a jig boring machine, preluding more elaborate machining sequences.  Following a precise cutting plan, the various workpieces are subject to a slow electro-discharge process according to a predefined pattern in order to remove part of the metal.  In fact, these components lose up to half of their initial volume in the course of the skeletonizing process.

Now machines yield to craftsmen.  First they need to check that the components have not been deformed in the cutting process, then their job is to embellish everything the eye can see.  The surface of every previously pierced and machined part is methodically touched up, circular grained then painstakingly bevelled by hand.

These components are then sent for engraving.  Vacheron Constantin is one of the very few manufacturers with an inhouse engraver; 25 year old Jeanne Ulrich who joined the brand two and a half years ago after completing a 4 year course in engraving.  "Sensitivity, rigor and exactitude in striving to attain perfection are the qualities which make a good engraver" says Jeanne Ulrich.

The engraving process begins with the "cementing" of the component to be engraved; this consists of firmly fixing it on a previously heated wax type material which solidifies once cooled.  The piece is then placed on a rotating bowl shaped tool enabling the engraver to hold the component in the desired position.

"It is as difficult to work on a time only movement as it is on a tourbillon or minute repeater because of the small surfaces and thin components" says Ulrich.  The main difficulty resides in the type of metal worked on, gold is a regular metal and easier to work with than maillchort (German silver) which has an irregular surface and hardness.

Once the components engraved (a single rotor can take up to half a day!), it is uncemented and bathed in different solutions to clean them of particles.

The watchmaker in charge of the watch now takes over, further refining the work and adding various finishing touches: the sink, or concave chamfer around each hole (in which the jewels are fitted) receive their final polishing with a diamond-tipped tool.  The mainplate, bridges and bars, mainspring barrel and hour wheel are then plated (either rhodium or red gold as for the new Patrimony Traditionnelle Perpetual Calendar)."

1924

Vacheron & Constantin's first skeleton watch.  Calibre RA 17''', rock crystal case circled in platinum with sapphires.  Photo reference 2479-81.

1925

Skeleton movement produced for American market under Merimont brand, Calibre 16''' 14/12.

1920s through 1930s

1929, Verger Frères

Twelve skeleton clock movements produced with double going-barrel and constant force remontoire d'égalité with spiral spring, straight-line lever escapement.  Only five clocks are known to be completed; three between 1932 and 33, and two cased in 1990s.

1953

Merimont skeletonized calibre in pink gold from 1925

1960

1978

Christies image

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