PVD and DLC are not the same thing, even though the visual result can seem identical. Confusing them is a common mistake I hear made even in serious watchmaking shops. It's worth distinguishing them with precision.
PVD, Physical Vapor Deposition, is a physical deposition process: the coating material — typically titanium nitride or chromium nitride — is vaporized under vacuum and deposited on the metal surface in a thin layer, typically between 2 and 5 microns. The result is a hard, adherent film, resistant to abrasion. The black variant is obtained by modulating the reactive gas during the process: nitrogen for the nitride, acetylene or methane to achieve darker tones. The Porsche Design Chronograph 1 from 1972 was the first commercial watch with an entire case coated in black PVD: at the time it was a radical technical and formal choice.
DLC, Diamond-Like Carbon, is instead a coating based on amorphous carbon, also deposited under vacuum but with different plasma processes — CVD or PECVD. The hardness is noticeably superior to that of traditional PVD: we're talking about values around 1500–3000 HV compared to 1000–1500 HV of titanium nitride. The thickness is even thinner, often under one micron. The color is opaque black, almost devoid of reflections, which in commercial jargon is called stealth. DLC is more expensive to apply and more demanding in terms of surface preparation: the surface must be perfectly clean and polished before deposition, otherwise the coating does not adhere uniformly.
In both cases, the coating is not permanent in the absolute sense of the term. With use, edges and contact areas show the first signs of wear before flat surfaces. This is not a defect: it is the physical nature of any thin film on a softer substrate. The steel underneath remains intact; it is the aesthetics that change.
A detail I often see overlooked: PVD applied to movement components — plates, bridges — also serves to create visual contrasts. In the Girard-Perregaux caliber 2967, the hand-polished borders emerge from the black surface with a depth effect that is not decorative in a superficial sense: it is the direct result of the finishing technique combined with the coating. Here the black is part of the technical language of the movement, not just the case.