Arnold & Son Pairs Gemstone Dials with Ultra-Thin Watchmaking in 2026

HM Pietersite

With the new HM Pietersite, Arnold & Son presents a watch whose appeal is based on a combination of material effect and historical depth. At first glance, this model seems extremely simple: two hands, no date, no additional display, a tidy dial. Yet it is precisely in this design that its strength lies. The HM Pietersite is a dress watch that does not rely on decorative excess. At the center is a dial made from pietersite, whose lively grain is reminiscent of turbulent water and dramatic sky formations — effectively a miniature landscape between storm and calm. Arnold & Son offers the new release in two limited versions: one in 18-carat red gold with an edition of only eight pieces, and one in stainless steel, limited to 18 pieces.

Like a Frozen Storm

The true centerpiece of this watch is its pietersite dial. The stone, a variety of chalcedony, was discovered in Namibia in the early 1960s. It is sometimes referred to as a “storm stone” due to its dramatic, lively structure. This designation fits perfectly here, as Arnold & Son uses pietersite not just as a decorative natural material but as a narrative medium. Its random, delicate yet vigorous grain is reminiscent of breaking waves or cloud formations over the sea. The reference to Cornwall, the birthplace of John Arnold, is more than just poetic embellishment. The rugged coasts and rough weather of this region seem to be captured in the dial. Each pietersite stone is naturally structured differently, giving each piece its own unique character.

Acronym with Historical Resonance

The name of the model is also carefully chosen. HM officially stands for Hours and Minutes, but at the same time, it refers to Great Britain’s maritime history. The manufacturer thereby echoes the naming of Royal Navy ships, where “HM” stood for Her or His Majesty’s, depending on the reigning monarch. This later became the well-known formula HMS, meaning Her Majesty’s Ship or His Majesty’s Ship. This historical reference is particularly fitting for Arnold & Son. The brand refers to John Arnold, one of the most important English watchmakers of the 18th century. His highly precise marine chronometers played a crucial role in improving navigation at sea.

Slim Case, Classic Proportions

The HM Pietersite measures 39.5 millimeters in diameter and is only 7.82 millimeters high. It appears present and elegant, but not fragile. The especially low profile is remarkable, as it ensures a very flat, refined fit on the wrist. The model is available either in 18-carat red gold or stainless steel. The red gold version naturally appears warmer and somewhat more classic, while the stainless steel variant emphasizes the cooler character of the pietersite dial. In both cases, the design language remains clear and reduced. A domed sapphire crystal with double-sided anti-reflective coating is used. The case back is also equipped with anti-reflective sapphire crystal, allowing the movement to remain visible. Water resistance is up to three bar.

Ultra-flat, Classic, and Enduring

Inside works the manufacture caliber A&S1001, a mechanical hand-wound movement that matches the character of the HM Pietersite. It measures 30 millimeters in diameter, only 2.7 millimeters in height, and operates at a frequency of 21,600 vibrations per hour. Particularly noteworthy is the 90-hour power reserve. The finishing of the movement also meets high watchmaking standards. The mainplate is rhodium-plated and perlage-finished, the bridges are beveled and decorated with sunburst Geneva stripes. Added to this are spiral wheels and blued screws with polished heads. The watch is completed by an ink-blue alligator leather strap, featuring a classic pin buckle in rose gold or stainless steel, depending on the case material.

The Arnold & Son HM Pietersite is a watch for collectors seeking character. It does not rely on spectacular complications or demonstrative mechanics, but on a very conscious reduction. It unfolds its narrative power precisely in its limitation to hours and minutes and is therefore compelling, showing how strong a seemingly simple watch can be when material, proportion, history, and movement are brought together with real consistency. The pietersite dial is the emotional core of the model.

Ultrathin Tourbillon Onyx

Exceptionally expressive is also the Ultrathin Tourbillon Onyx. The editions, limited to eight pieces each in 18-carat rose gold or platinum, combine extreme thinness with a similarly distinctive choice of material: onyx, a deep black stone that here serves not only as a decorative element but becomes the actual stage of the watch.

Between Depth and Contrast

The watch’s dial is made of a finely crafted disc of genuine onyx, a variety of agate from the chalcedony family. Its deep black, almost light-absorbing surface gives the watch an extraordinary presence. Unlike many stone dials, which stand out through graining or color play, the onyx here thrives on its apparent homogeneity. Arnold & Son goes a step further by not only polishing the onyx but also finishing it with matte and satin textures. This technically demanding finish creates subtle contrasts within the same material. The large main dial appears deeply glossy, while the concave subdial for hours and minutes has a matte, almost velvety surface. The eye is also drawn to the center, where at six o’clock the cage of the flying tourbillon opens and stands in deliberate contrast to the dark surface.

Flying Tourbillon as Narrative Center

The tourbillon of the Ultrathin Onyx is not only a technical element but also a bearer of symbolism. The polished, satin-finished, and hand-angled cage completes a full rotation in 60 seconds and thus also functions as a seconds display. The design incorporates historical motifs. A stylized sextant refers to maritime history and the importance of precise timekeeping for determining longitude at sea. The anchor-shaped counterweight is reminiscent of classic marine instruments and iconic creations by John Arnold.

Ultra-flat and Highly Efficient

Inside works the manufacture caliber A&S8300, a hand-wound movement with a flying one-minute tourbillon. With a height of only 2.97 millimeters, it is one of the flattest tourbillon calibers ever. The movement measures 32 millimeters in diameter, has 29 jewels, and operates at a frequency of 21,600 vibrations per hour. Particularly impressive is the 100-hour power reserve. This is made possible, among other things, by a revised regulating group with variable inertia, more precise fine adjustment, and structural changes to the tourbillon cage. The finishing meets the standards of haute horlogerie. The mainplate is perlage-decorated, the bridges are polished, hand-chamfered, and decorated with sunburst Geneva stripes. The wheels are circular satin-finished, and the screws are blued, chamfered, and high-gloss polished. This craftsmanship is visible through the sapphire crystal case back.

Elegance in Its Purest Form

The case of the Ultrathin Tourbillon Onyx measures 41.5 millimeters in diameter with an overall height of only 8.4 millimeters, including the crystal. Despite the tourbillon, it remains flat, balanced, and remarkably wearable. The slim bezel emphasizes the openness of the dial, while the domed, double-sided anti-reflective sapphire crystal adds depth. Water resistance is three bar. The price for the rose gold version is approximately $95,000, while the platinum version is offered for about $109,000.

The Ultrathin Tourbillon Onyx demonstrates how powerful a seemingly minimalist concept can be. The deep black onyx becomes the stage, the flying tourbillon the protagonist, and the ultrathin caliber A&S8300 forms the invisible foundation of this timepiece. It avoids visual excess and instead focuses on precision, material quality, and fine detail, presenting one of the more refined interpretations of modern haute horlogerie.

To learn more, visit Arnold & Son, here.