Unveiling the Grand Seiko Kodo Constant-force Tourbillon

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In 2022, Grand Seiko presented its first mechanical complication, the Kodo Constant-force Tourbillon, a revolutionary watch that combined a tourbillon and a constant-force mechanism as one unit on a single axis for the first time in horological history. As such, it represented a major milestone in the history of Grand Seiko and was recognized by the international watch community when it was awarded the Chronometry Prize at that year’s Grand Prix d’Horlogerie de Genève. Today, the Kodo story unfolds with the introduction of a limited-edition timepiece inspired by daybreak; its design perfectly complements that of the first.

The daybreak of Kodo

While the first Kodo expressed evening twilight through the delicate interplay of light and shadow that is central to Grand Seiko aesthetics, the new timepiece uses light and shadow to evoke daybreak. The delicate time when morning light begins to reclaim the sky is emphasized throughout the design. This watch completes a portrayal of light and shadow that began two years ago.

While both Kodo watches are expressions of light and shadow, the brightness of the new creation is a vivid
counterpoint to the darkness of the first. — While both Kodo watches are expressions of light and shadow, the brightness of the new creation is a vivid counterpoint to the darkness of the first.

The movement components have a silver tone, giving the new Kodo a subtle but bright appearance that accentuates the intricately constructed and layered parts. The beauty of the painstakingly hand-polished components is even more pronounced in the new timepiece.

Masterpiece Collection Grand Seiko Kodo Constant-force Tourbillon

For the first time in a Grand Seiko watch movement, blue sapphires are used for the jewels, adding an unexpected detail that is in perfect harmony with the design. Carefully examined and selected, the pale blue sapphires recall a beautiful dawn.

Grand Seiko Kodo Constant-force Tourbillon

The open-work design not only reveals the beauty of the hand-finished movement, but the open spaces themselves have been carefully considered to reflect an important Japanese cultural and aesthetic value that respects the use of empty space. The use of open space is also reflected in the lugs, which harmonize with the case and add lightness to the design.

A subtle gradation of light is expressed through the use of different materials and various types of finishing. Platinum 950 forms the watch’s inner case, while Brilliant Hard Titanium, an alloy twice as hard as stainless steel, forms the outer case, making the exterior highly resistant to scratches. The combination of the two materials creates a natural gradation and a long-lasting beauty. Some of the case parts in both metals are Zaratsu polished to a distortion-free mirror finish, while others have a hairline finish. Each process is completed by hand by highly skilled craftsmen and women to ensure that an elegant visual harmony is revealed from every angle.

The innovative Caliber 9ST1

The watch is powered by the uniquely innovative Caliber 9ST1, in which a constant-force mechanism and a tourbillon are set as one unit on a single axis. Because there are no wheels or other components between the two mechanisms, there is no loss or change in the torque transmitted from the constant-force mechanism to the balance wheel, which leads to a duration of approximately 50 hours for the constant-force mechanism and a highly stable amplitude for the balance. Together, these characteristics contribute to the movement’s high level of stable accuracy. Moreover, the Grand Seiko Standard for Constant-force has been established for Caliber 9ST1 in which each movement is tested for a full 48 hours in each of six positions and at three temperatures, a duration that is double the main Grand Seiko Standard and the industry standard. Each movement is assessed over the course of 34 days to verify its accuracy.

The movement consists of approximately 340 components, but more than 100 of these are packed into the “heart” of the movement, the integrated constant-force carriage and the tourbillon carriage, which is just about 10mm in diameter. On the constant-force carriage, a single red ruby is placed on one of the arms indicating the seconds as they pass.

The new timepiece shares the same hallmark as the first Kodo, which is the dazzling visual and audible effect created by the integration of the two mechanisms. The inner tourbillon carriage rotates while the balance steadily vibrates at eight beats per second, and the outer constant-force carriage follows its rotation in exact one-second intervals. The sounds of the escapement and the once-per-second impulse of the constant-force mechanism harmonize with this visual rhythm to create, for eye and ear, a deeply satisfying and reassuring heartbeat. There is a powerful yet gentle charm to this sound, which is set to a 16th note or semi-quaver.

An exclusive white strap

The watch is offered with a leather strap created from a highly durable material that is specially treated in the same traditional way once used in samurai armour. But this time, a new white colour was developed specifically for the new Kodo. The white strap is made through tanning with natural materials and then carefully hand-coated with layers of white urushi lacquer to create a deep sheen and a unique texture. A crocodile strap in charcoal grey also comes with the watch.

Made at Atelier Ginza

This creation is designed and assembled by an elite group of Grand Seiko designers and watchmakers at Atelier Ginza, a creative studio established to deliver unique and innovative mechanical timepieces of the highest order. A logo identifying its production at Atelier Ginza is engraved on the movement.

The new timepiece joins the Grand Seiko Masterpiece Collection as a limited edition of 20 and will be available at the Grand Seiko Boutiques starting in December 2024.