Jaquet Droz Tourbillon Plasma Ceramic Oberalp: How Plasma Treatment Turns White Zirconia Asphalt Gray

Plasma Ceramic: What Firing Above 20,000°C Actually Does to Zirconia

The Jaquet Droz Tourbillon Plasma Ceramic Oberalp is a single unique piece, commissioned by a private collector and delivered in September 2026. Its case is 42 mm in diameter, made from ceramic, and finished in a matte asphalt gray achieved through what Jaquet Droz describes as an in-house plasma treatment process. The base material is white. The colour is not a coating applied after the fact. It is produced by firing at temperatures exceeding 20,000°C—a figure that immediately separates this process from conventional zirconia sintering, which typically operates in a range several orders of magnitude lower.

That distinction matters to anyone involved in ceramic case production. Standard yttria-stabilized zirconia is sintered in the range of roughly 1,400°C to 1,600°C, where densification occurs and the tetragonal phase is stabilized. What Jaquet Droz refers to as plasma firing operates at temperatures far beyond that threshold, in territory associated with plasma arc or plasma torch processing rather than conventional furnace sintering. At those energy levels, the interaction between the ceramic surface and the plasma environment can drive changes in surface chemistry, grain boundary character, and optical absorption that a standard sintering cycle simply cannot replicate. The result here is a shift from white to asphalt gray—a matte, delicately sandblasted finish—while the bulk of the material retains the mechanical properties that make zirconia attractive for case construction in the first place: hardness, scratch resistance, and low density relative to steel.

The sandblasting step mentioned in the process description is not incidental. After plasma treatment, the surface requires mechanical refinement to achieve the controlled matte character the brand describes. Sandblasting on a plasma-treated ceramic surface is a precision operation. The material is hard enough that abrasive media selection and pressure parameters have to be tightly controlled to produce a uniform texture without introducing subsurface cracking or disrupting the colour uniformity achieved during firing. Any inconsistency in the blasting step would show immediately on a surface this colour—asphalt gray has very little visual tolerance for variation in gloss or texture.

Machining a Plasma-Treated Ceramic to 42 mm

Ceramic case machining is always a constrained problem. Zirconia’s hardness means that material removal requires diamond tooling, and the brittle fracture behaviour of ceramics means that cutting parameters—feed rate, depth of cut, coolant strategy—have to be managed carefully to avoid chipping at edges and apertures. For the Oberalp case, the geometry includes a 42 mm diameter and provisions for a crown, caseback, and the integration of a mixed folding clasp that combines ceramic and steel components. That clasp junction is itself a small engineering problem: ceramic and steel have different coefficients of thermal expansion, and the interface between them has to be designed so that dimensional changes across the service temperature range do not introduce stress concentrations at the joint.

The plasma treatment step in the production sequence also has implications for when machining occurs. If the ceramic blank is plasma-treated before final machining, the cutting process risks exposing untreated subsurface material at machined edges and apertures, breaking the colour continuity. If plasma treatment is applied after machining, the geometry of the finished case has to survive the thermal and atmospheric conditions of the plasma process without distortion or cracking—a non-trivial requirement for a component with tight dimensional tolerances. Jaquet Droz describes this as an in-house specialty, which suggests the sequencing and process parameters have been developed and controlled internally rather than sourced from a generic industrial ceramics supplier.

Movement and Finishing: The 8-Day Tourbillon Inside

The movement is the Jaquet Droz 8-Day Tourbillon. For this piece, the workshop reproduced a two-tone aesthetic: black galvanic treatment on the movement finishing, with a polished tourbillon standing out against that dark ground. Black galvanic treatment on movement components is a surface engineering process in its own right—the layer has to be uniform in thickness and adhesion across the complex three-dimensional geometry of bridges and plates, and it has to remain stable under the thermal cycling and lubricant exposure of normal service. The contrast between the polished tourbillon cage and the treated movement surfaces is a deliberate optical choice, but it is also a quality control checkpoint: any inconsistency in the galvanic layer becomes immediately visible against the polished reference surface of the tourbillon.

The oscillating weight is the most mechanically complex component in this piece. The collector requested that it reproduce a wheel rim from his V12 supercar—a design described as among the most complex in the automotive world, with an aerodynamic multi-level spoke profile and a yellow center cap. Jaquet Droz executed this in white gold, profiling six spokes across multiple levels to capture the three-dimensional character of the automotive original. White gold was chosen specifically to enhance the visual effect of the kinetic movement of the rotor. Machining a white gold rotor to that spoke geometry requires multi-axis CNC work and subsequent hand finishing to achieve the surface quality expected at this level.

Dial Construction: Sapphire, Gold, and Miniature Painting

The dial construction layers a sapphire crystal plate over a gold dial base. The miniature painting on the sapphire plate depicts the collector’s supercar on the Oberalp Pass bend, with the Andermatt peaks in the background—executed entirely by hand. Painting on sapphire presents adhesion challenges that painting on metal does not: the surface is chemically inert and extremely smooth, so the paint medium and application technique have to be matched to the substrate. The gold dial base beneath provides both the structural foundation and the reflective ground that gives depth to the painted scene when viewed through the sapphire layer above.

As a one-of-a-kind commission developed through Jaquet Droz’s Studio 8 co-creation process, the Oberalp piece represents a manufacturing sequence that integrates plasma ceramic case production, black galvanic movement finishing, multi-level white gold rotor machining, and hand miniature painting on sapphire into a single object. Each of those processes carries its own tolerance stack and quality control requirements. The plasma ceramic case is the most technically novel element, and the questions it raises about sintering sequence, colour stability at machined edges, and the long-term behaviour of a plasma-modified zirconia surface under real service conditions are ones that ceramic case manufacturers across the industry will be watching as this process matures.