Introduced in 2010 as the part of Bulgari Daniel Roth collection, the Bulgari Grande Lune offers a brilliant interpretation of the path of the moon expressed in the most elaborate horological form, since an astronomical moon-phase display is a world away from corresponding traditional indications.
The real lunar cycle lasts 29 days, 12 hours, 44 minutes and 2.8 seconds, an extremely accurate duration that watchmakers have sought to reproduce as accurately as possible.
In the vast majority of cases, the micromechanical transcription of moon-phases generally comprises two complementary moving parts: the first wheel and pinion performs a complete rotation in 24 hours, while the disc carrying the moon is equipped with 59 teeth and displays the lunar-cycle in 29 days and 12 hours. Compared with the actual lunar orbit, the difference in time accumulated by this construction thus amounts to 44 minutes and 2.8 seconds per month. After exactly 32 months, this device thus leads to a one-day discrepancy compared with the celestial reality and therefore requires manual adjustment.
In the case of an astronomical moon-phase display, better known by enlightened amateurs as a high-precision moon phase, the construction itself achieves enhanced precision by complementing the first wheel and pinion with a 7-toothed star and a 135-toothed moon disc. The first performs a rotation in 24 hours, the 7-toothed star rotates in 7 days, and the disc bearing the moon displays an extremely accurate lunar cycle of 29 days, 12 hours and 45 minutes – thus reducing the precision error to just 57.2 seconds per cycle. After the first year, the discrepancy amounts to 11 minutes and 26.4 seconds, which means it is not until more than a century later – 125 years in fact – that this high-precision mechanism will need to be manually adjusted.
Positioned on a depiction of the night sky, the central fine gold-coated moon is revealed through an asymmetrical opening topping the extremely original seconds indication. The latter – a signature feature of the Bulgari Daniel Roth Collection – is composed of three arms of varying lengths spinning on a single axis and respectively covering three 20-second segments. The dial displays the date on a graduated circle subdial, and the lunar cycle and date functions are easily adjusted using the two corrector pushpieces on the side of the slender elliptical rose gold case.
The entire set of functions is driven by the generously sized 15’’’ DR Calibre 2300, a Lépine-type mechanical hand-wound Frédéric Piguet movement enriched with an exclusive Daniel Roth complication. The seconds hand is positioned along the same axis as the winding-stem. The movement is entirely hand-decorated and boasts exceptional finishing including a circular-grained mainplate, chamfered and polished bridges featuring Côtes de Genève decorative motif, as well as polished screw heads.
The BULGARI GRANDE LUNE comes dressed in a simple 44 mm-diameter elliptical case crafted in 18-carat rose gold and water-resistant to 30 metres, topped by a split-level dial featuring white-lacquered and black gold satin-brushed surfaces, along with 18-carat rose gold-coated hands and hour-markers. The Grande Lune model is fitted with an alligator leather strap equipped with a rose gold pin buckle.
Model: BULGARI GRANDE LUNE, Manual Winding, Rose Gold (From Bulgari Daniel Roth collection 2010)
Reference: DR2300, mechanical hand-wound calibre
Diameter: 15 lignes
Jewelling: 32 jewels
Power reserve: 42 hours
Frequency: 3 Hz – 21,600 vph
Winding: Via the crown
Balance: Three-spoke ring balance in Glucydur with poising screws
Index assembly: Sliding plate and stud with round head and collar
Rating: 5 positions
Bridges: Côtes de Genève decorative motif
Bridge rims: Chamfered and polished on the lathe
Going train: Circular satin-brushed wheels and chamfered spokes
Jewel, screw and pin surrounds: Tone-on-tone diamond-polished
Hours, minutes, three-armed small seconds hand rotating across three 20-second segments; central astronomical moon-phase disc; pointer-type date display on a circular subdial.