Timekeepers Club / May 6, 2022

Arnold & Son Ultrathin Tourbillon in Red Gold or Platinum with Cosmic Grené Dial

The ultrathin tourbillon by Arnold & Son is offering two new designs. They feature a new type of dial with tinted gold and aluminium sparkles to match their precious cases, which have also been redesigned. In 5N red gold or 950 platinum, the cases are just 8.3 mm thick beneath their domed sapphire crystals. The offset display and the tourbillon aperture echo the way in which information was arranged on John Arnold’s marine chronometers. After reworking the structure and appearance of the rotating regulating organ, the power reserve now lasts at least 100 hours – an outstanding and noteworthy performance for an ultrathin tourbillon timepiece.

To give the Ultrathin Tourbillon a new unique and refined design, Arnold & Son has focused on materials and techniques that highlight the precious appearance of this finely honed tourbillon. The 41.5 mm cases in 5N red gold or 950 platinum have been redesigned, making them even slimmer and more refined. The bezels have been reduced to a fine metal band, the sapphire crystals are domed, and the transparent case backs have been screwed down.

Beneath the stars

Arnold & Son has used a new manufacturing technique known as ‘Cosmic Grené’ on the dials. This name makes direct reference to stargazing, as stars are essential guides for navigating at sea along with marine chronometers (of which John Arnold was one of the largest and most reputable suppliers).

Gold powder mixed with aluminium sparkles has been placed on the dial plate to create a lightly sandblasted surface. This is then coloured: blue for the Ultrathin Tourbillon in red gold, and green for the platinum version. Due to the complex manufacturing methods involved, these dials are subtle and finely textured, with a discreet lustre.

Latest-generation carriage

At the heart of the Ultrathin Tourbillon lies the A&S8300 calibre, whose architecture and finesse characterise this collection. At just 2.97 mm thick, this tourbillon with extremely refined finishes is one of the slimmest ever designed.

The highest point of the A&S8300 calibre is located on the top of the tourbillon carriage, which has also been redesigned and undergone significant changes in relation to its predecessors. It features a variable-inertia balance with inertia blocks to ensure more stable calibration over time. The redesigned tourbillon carriage echoes the leading role John Arnold played in marine exploration during the 18th century. Its triangular shape evokes a sextant, while its double-arrow counterpoise represents an anchor. The point in the middle serves as a seconds marker, as the carriage completes a full rotation in one minute.

Golden time

The back of the Ultrathin Tourbillon reveals a new rear tourbillon bridge in 3N yellow gold that matches the gear train and stands out from the appearance of the rest of the calibre.

Modifications to the tourbillon carriage and regulating organ have increased the power reserve of the A&S8300 calibre, which now lasts at least 100 hours. This long power reserve meets the performance standards of Arnold & Son calibres.

Technical specifications

Arnold & Son Ultrathin Tourbillon

Reference: 1UTBR.U01A.C209A (red gold)

Reference: 1UTBR.XF01A.C208A (platinum)

Limited edition of 28 pieces for each version


  • Material: 18-carat (5N) red gold or Pt950 platinum
  • Diameter: 41.50 mm
  • Thickness: 8.30 mm (with crystal)
  • Crystal domed sapphire, with an anti-reflective coating on both sides
  • Case back sapphire crystal, with an anti-reflective coating
  • Water-resistant to 30 metres / 100 feet

Dial and hands

  • ‘Cosmic grené’: gold powder mixed with coloured aluminium sparkles flange: coloured and circular satin-finished
  • Hour dial base: white mother-of-pearl, domed ring: rhodium-plated or with 4N gold plating


  • Calibre A&S8300, 1 minute flying tourbillon, manual winding
  • Number of jewels: 29
  • Diameter: 32.00 mm
  • Thickness: 2.97 mm
  • Power reserve 100 hours
  • Frequency: 21,600 vph (3 Hz)


  • main plate: Côtes de Genève stripes radiating from the centre
  • bridges: polished and chamfered by hand
  • wheels: circular satin-finished
  • screws: blued and chamfered, mirror-polished heads
  • tourbillon carriage: ‘Arnold & Son’ signature
  • rear tourbillon bridge: 18-carat (3N) yellow gold, sunray motif


  • Hour, minutes

Strap and buckle

  • Material: blue alligator leather hand-stitched with 18-carat (5N) red-gold thread or green alligator leather, hand-stitched with pt950 platinum thread
  • Folding clasp with top cover in 18-carat (5N) red gold or Pt950 platinum


  • CHF 73'300 (red gold)
  • CHF 85'100 (platinum)

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