Surface deposition

PVD, CVD, and ALD are three distinct processes that share the same underlying logic: depositing an ultra-thin layer of material onto a solid surface, without chemical bath immersion and without traditional electroplating. The difference between them is not aesthetic but physical, and it's worth keeping clear because the results in terms of durability and color change substantially.

PVD, Physical Vapor Deposition, works under high vacuum: the coating material is physically vaporized, by sputtering or evaporation, and condenses on the piece's surface. It's used to coat cases, bezels, casebacks, hands, and indices. The most common colors are black (titanium nitride or zirconium nitride), anthracite, dark gray, and golden tones. The layer is hard and abrasion-resistant, but it's not indestructible: a blow to a sharp edge can chip it, because the underlying metal gives way before the coating. Anyone who wears a black PVD watch and bangs it against a door handle already knows this.

CVD, Chemical Vapor Deposition, deposits material through a chemical reaction in the vapor phase: gaseous precursors react on the heated surface and form the desired layer. Compared to PVD, it follows complex geometries better and can create special optical effects, such as the green-blue iridescence seen on certain modern dials or the historic blue-gray replicated on reissues of 1960s sports chronographs. CVD is also the process used to grow carbon nanotubes for certain high-end watchmaking components: TAG Heuer's TH-Carbonspring spiral, for example, forms directly during CVD growth, collet included, eliminating a critical assembly step.

ALD, Atomic Layer Deposition, is the most precise of the three processes. It deposits material layer by atomic layer, with thicknesses controlled in the nanometer range. The result is an absolutely homogeneous film even on irregular surfaces. In watchmaking it's found on dials, bridges, plates, and hands: the ALD blue of certain Urwerk or Breguet dials has a color depth that no standard PVD can replicate, because the thickness is controlled with a precision that modifies the optical properties of the layer. It's still a costly treatment and not widespread, but growing.

From the bench: PVD ages visibly, especially on the case edges. CVD on dials is generally more stable because the piece doesn't undergo the mechanical impacts that the case does. ALD remains the least known to customers, but those who see it in person usually recognize it immediately for the quality of its color.