Leroy Osmior Chronomètre à Tourbillon

The Chronomètreà Tourbillon is a masterpiece joining the new OSMIOR collection designed as a tribute to the wealth of the Leroy chronometric heritage. Beneath its extremely pure appearances, respectful of the codes and traditions of fine French horology, lies an ingenious and innovative mechanism. The historical references and the movements used in chronometry competitions – competitive arenas for watchmakers until the 1970s – naturally determined the choice of the tourbillon.

This heritage lives on, since the victory earned in the 2013 International Timing Competition in the Tourbillon category was added to the 384 gold medals already won by Leroy.

Hand-wound Manufacture Calibre L100, entirely developed and built in the Manufacture in Le Sentier at the heart of the Vallée de Joux, has an escapement with direct impulse on the balance also featuring an impulse wheel and a winding wheel for constant force, as well as a balance-spring with two terminal curves. The movement is housed within an elegant 41 mm-diameter round case in gold(5N red gold, palladium-coated white gold or two-tone) framing a magnificent Grand Feu enamel dial, inspired by 19th century Leroy pocket watches.

This unprecedented calibre is an authentic horological mechanical masterpiece with its 953 parts, almost as many as the iconic historical Leroy 01. The movement architecture and its pillar-based construction are inspired by the first 18th century marine chronometers. The barrel-bar is enhanced by a now extinct traditional technique involving hand brushing with silver powder to create a grained texture.

The time-setting mechanism, a nod to 18th century French clockmaking, is adorned using the Geneva mast” decorative technique, while the finesse and geometry of the going train are also inspired by the same era.

The calibre comprises an original direct-impulse escapement (one direct impulse and one indirect impulse per oscillation) recalling the “Duplex” escapement developed by Pierre Le Roy and protected by a patent registered for its ingenious self-compensating mechanism for thermal variations. The balance is thus equipped with a system serving to compensate for the undesirable effects (such as disturbances to rating precision) caused by the dilatation of the balance-spring, at temperatures extending beyond those normally controlled within a horological mechanism. The use of diamond impulse-pallets also stems from a determination to limit friction and thereby increase the efficiency of energy transmission, as well as reducing wear.

The balance with four adjustment screws is equipped with a balance-spring produced by Manufacture de Spirauxet Echappemments (MSE) which, like Leroy itself, belongs to the Festina group. This balance-spring is distinguished a double terminal curve such as described in watchmaking theory but never previously used in series-made models and now assembled in the Leroy workshops. There are two curves – an inner curve and an outer curve – that foster isochronism while ensuring perfectly concentric deployment in a vertical position.

These two curves also eliminate any potential “unbalance” effect, the disequilibrium referred to in watchmaking literature as the “Grossmann effect” (named after Jules Grossmann, 1829-1907). They also serve to neutralise the so-called “Caspari effect” (named after the head of the chronometry department of the French Royal Navy in 1900). The latter’s research was itself based on the discoveries made by Pierre Le Roy, whose empirical observations showed him that that there is in every spring a certain length that endows it with perfect isochronism, a principle he was able to apply to balance-springs.

The calibre oscillates at 18,000 vph (2.5 Hz) with a large-size balance that promotes long-term precision rating. An integral part of the escapement, the constant-force device serves to ensure stable amplitude throughout the duration of the power reserve.

Also based on the idea of maintaining the most stable possible deployment of energy over the entire power reserve, the fusee-chain device guarantees exemplary linearity of the torque in order to supply the energy required to rewind the constant-force escapement. The chain itself is a marvel of miniaturisation and precision comprising 105 links measuring 1.55 cm each and forming a total length of 16.275 cm.

The aesthetic of the tourbillon carriage harks back to the 18th century, as does the gear train. Its bridge is mirror-polished. In tribute to Pierre Le Roy, the first watchmaker to have produced a deck chronometer for maritime navigation, Leroy has selected a deadbeat seconds mechanism enabling the seconds hand to literally pause for a second to mark this unit of time. Inspired by the same idea as that featured on the Duplex escapement with its double escape-wheel, two superimposed but connected levers serve to deconstruct the seconds jump into two phases.

The Chronomètre à Tourbillon displays the hours, minutes and central deadbeat secondsby means of cut-out steel hands. The power reserve is indicated by a subtle touch representing a nod to Julien Le Roy (father or Pierre Le Roy), inventor, of the à toc watch featuring a discreet indication of this function. The lozenge-shaped marker is painted on a Grand Feu enamel disc applied to the dial and visible beneath a grid reminiscent of the tapestry motif on the snuffbox-watch made for Marie-Antoinette and dated 1788 (Leroy Museum collection, signed Basile-Charles Le Roy). A disc spinning counter-clockwise on a 300° axis between 11 and 1 o’clock indicates the 75-hour power reserve.

The design scrupulously respects the signature features of the works of art from past centuries bearing the Leroy signature, embellished by a variety of artistic craftsmanship techniques notably including a finely chased grid placed on top of the dial and reproducing the tapestry motif of an historical watch made for Marie-Antoinette.

The dial is adorned with grand feu enamel and features champlevé Roman numerals – satin-brushed on the ivory-toned version and polished on the royal blue variation – standing out from the underlying gold plate.

The round case embodies a subtly sophisticated style with integrated lugs and comes in three versions: 5N red gold, palladium-coated (non-rhodiumed) white gold and a two-tone variation. It is composed of four parts: polished bezel, circular satin-brushed case middle, polished gadroons and lugs, and a guilloche hinged back cover.

The choice of this hinged back cover adorned with a hand-crafted barleycorn guilloché motif was inspired by 19th century Leroy pocket watches. The back cover is opened by a device on the crown that unlocks the “secret” caseback to reveal the magnificent Calibre L100 through a sapphire crystal pane.

The movement wheels are burnished and polished according to the highest quality standards. As ever showing consistent respect for the traditional rules governing the decoration of high-end objects, the pinion leaves are polished using a wooden grinding wheel. The steel parts are polished or adorned using a “Geneva mast” decorative technique. The barrel-bar is decorated with a “silver-powder” grained texture applied by manual brushing. All the screws are blued from the outset to prevent oxidation, while the screw heads are polished and even the profiles of the collets/ridges/convex hole surrounds are also polished.

The timepiece is fitted with a hand-sewn alligator leather strap lined with alcantara and secured by a pin buckle of twin-blade folding clasp.

Each Chronomètre à Tourbillon timepiece undergoes the chronometry certification procedure conducted at Besançon Observatory and earns a chronometer rating certificate that is delivered with the watch. The Besançon Observatory tests the entire watch ‘head’ (meaning a fully cased up model not yet fitted with its strap/bracelet) for 15 days, and only after successfully passing these merciless trials is each main-plate hallmarked with the “Viper’s Head” symbol.

Technical details
Manufacture Calibre L100
Mechanical hand-wound
15 ½ ‘’’ in diameter 35.3 mm)
7.5 mm thick
Shape: Round
Jewels: 42 in sapphire and 14 in diamond
Power reserve: 72 hours
Frequency: 18,000 vph (2.5 Hz)
Barrel: Variable torque by fusee-chain transmission
Escapement and regulating organ: Direct impulse on the balance by one large direct impulse and one small indirect impulse per oscillation
Balance with screws and thermal self-compensating mechanism (patent filed)
13 mm diameter
Guided by an impulse wheel and a winding wheel for constant force
Unlocking lever with 2 diamond pallets
Unlocking adjustable diamond impulse pin
Balance-spring with double terminal curve: 1 inner curve and 1 outer  “Breguetovercoil” Phillips curve.

Central hours and minutes
Central deadbeat seconds
Painted lozenge-shaped power reserved indicator appearing on grand feu enamel disc rotating counter-clockwise over a 300° angle between 11 and 1 o’clock.

Diameter: 41mm
Thickness: 15.26mm
18K 5N red gold – non-rhodiumed 18K 150Pd-coated white gold – two-tone white and red gold
Round, four parts including hinged back cover adorned with barleycorn guilloché motif and crown-activated “secret” mechanism
Circular satin-brushed case middle – polished bezel and gadroons
Polished caseback and dial fitted with glare proofed sapphire crystals
Water resistance to 3 ATM

Ivory-toned or royal blue grand feu enamel in 18K gold base
Satin-brushed or polished champlevé 18K gold Roman numerals
18K gold chased grid adorned with “Marie-Antoinette” tapestry motif, placed above the power-reserve indicator disc
Power-reserve indicator disc rotating over a 300° angle between 11 and 1 o’clock
Steel Leroy hands in rhodium, 5N gold or anthracite, or blued
Transferred railtrack taupe-coloured (for ivory-toned dial) or ivory-toned (for royal blue dial) chapter ring

In hand-sewn brown, black or blue alligator leather with large square scales and hand-sewn alcantara lining
Pin buckle or double-blade folding clasp in 18K white gold or 5N red gold

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