Finnish watchmaker Stepan Sarpaneva has revealed the newest iteration of his trademark complication, the Lunations Black Ruthenium.

Equipped with his proprietary moon phase movement, the Lunations moon phase is so accurate it will accumulate a mere one-day discrepancy after 14,000 years. Limited to just ten pieces, this is a variant of a model first introduced a dozen years ago, but remains the brand’s most complex wristwatch.

Initial thoughts

The Lunations has all of the Sarpaneva design elements, including the moon “face”, open-worked dial (which in this case is actually the movement), laser engraved decoration as well as hand finishing, so it resembles many of the brand’s other watches. But the Lunations is actually one of the most complex watches devised by Sarpaneva.

The Lunations is unusual in combining both the brand’s recognisable design with an original movement, one developed with the help of Andreas Strehler, whereas most of Sarpaneva’s other watches are powered by simpler, outsourced movements. 

Constructed in a novel manner with a two-disc moon phase display that’s so large it’s almost the diameter of the movement, the calibre inside is both interesting and complex. However, a moon phase complication is usually simple – and inexpensive – in most other watches.

Consequently, the Lunations feels pricey with its €39,500 price tag, particularly so considering that Sarpaneva’s other moon phase models powered by outsourced movements cost half that. But the price of the Lunations is arguably justified due to the elaborate nature of the movement, as well as the small production run of just ten watches.

Lunar skeleton

The Lunations is powered by the “Moonment”, a calibre conceived in collaboration with Andreas Strehler, who has his own brand but also supplies many of his fellow independent watchmakers with movements and components. Hand-wind with a 60-hour power reserve, the Moonment has an unusual layout with the going train and balance occupying the top half of the movement, while the barrel sits at nine o’clock.

This leaves the lower third of the movement empty for the oversized moon phase display that is achieved with twin moon discs visible on the open back. The discs are each engraved with an arrow that is read in tandem with the scale engraved on the case back, giving a precise reading of the age of the moon.

While the unusual layout and skeletonisation are its most apparent features, the Moonment has an especially accurate moon phase. By refining the gear ratio to the highest possible resolution, the moon phase is accurate to a day in 14,000 years. In contrast, a conventional moon phase (that is often linked to the date mechanism), has an error of a day in 122.5 years.

The movement is almost entirely traditional in its materials, save for the moon phase display window, which is made of optical fibre that’s been laser engraved and then hand finishing. The optical fibre magnifies the moon disc that is located on the rear of the movement and visible through the open back.

Notably, the moon disc is made of Lumicast, a resin impregnated with Super-Luminova. It appears white in daylight but also glows white in the dark. 

The rest of the calibre is executed in Sarpaneva style, with radially an open-worked base plate. Though this iteration of the Lunations remains mechanically identical to the earlier versions, it has been reworked in terms of design. 

Changes include the black ruthenium of the base plate and bridges, and more significantly, the removal of the chapter ring with hour markers, which gives the dial a cleaner, more mechanical appearance. 

Furthermore, the Lunations Black Ruthenium can be customised by varying the colour of the hands, with options ranging from black, red gold, flame blueing, or rhodium plating.

The Lunations is encased in the distinctive Sarpaneva Korona case with its notched silhouette. Made of a stainless steel from a Finnish smelter, it measures 42 mm in diameter and stands 9.8 mm high. 

Key facts and price

Sarpaneva Lunations Black Ruthenium

Diameter: 42 mm
Thickness: 9.8 mm
Material: Stainless steel
Crystal: Sapphire
Water resistance: 50 m

Movement: Moonment calibre
Functions: Hours, minutes, and moon phase
Winding: Hand-winding
Frequency: 21,600 beats per hour (3 Hz)
Power reserve: 60 hours

Strap: Leather with pin buckle, additional rubber strap

Limited edition: Ten pieces
Availability: Direct from Sarpaneva
Price: €39,500 excluding taxes (about US$42,400)

For more, visit Sarpanevawatches.com.