DLC coating

DLC stands for Diamond-Like Carbon: amorphous carbon deposited in an extremely thin layer on metal surfaces through vacuum processes, typically CVD (Chemical Vapour Deposition) or PVD. It's neither a paint nor a traditional plating. It's a carbon lattice that approaches diamond in structure, and this determines its properties: extremely high hardness, low friction, and decent chemical resistance.

From the workbench I see two recurring misunderstandings. The first: DLC and black PVD are confused because they look similar. They're different processes. PVD deposits metals or metal nitrides; DLC deposits carbon. The Vickers hardness of DLC can exceed 3000 HV compared to the typical 1200-2000 HV of titanium nitride-based PVD. The second misunderstanding concerns color: DLC doesn't necessarily mean opaque black. The tone depends on the film composition and underlying substrate. You get deep glossy blacks, brushed anthracites, almost neutral grays. Bulgari uses it on the Octo Finissimo titanium for a matte black that it considers more coherent with the case architecture than glossy ceramic. Ressence applies it in glossy version on titanium. MING 37.02 Monolith brings it in anthracite on brushed surfaces.

Typical thickness is between 1 and 5 microns. Such a thin layer doesn't alter the mechanical tolerances of the case, but this only holds if the piece was dimensioned upstream with the coating already planned. On pieces not designed for DLC, an out-of-spec layer can cause assembly problems with pressure-fitted bezels or threaded casebacks.

Durability is superior to standard PVD, but it's not indestructible. Concentrated blows on thin edges can chip the film. Once chipped, DLC doesn't repair locally: you have to remove the entire coating and reapply it, an operation that few laboratories in Italy are equipped to do. The exposed metal substrate at a chipped point is vulnerable to oxidation, especially on common steel.

In watchmaking, DLC is used on cases, bezels, crowns, casebacks, pushers and buckles. On titanium it works particularly well because titanium is already lightweight and unreactive, and DLC compensates for its relatively low surface hardness. On 904L steel, as in the Bremont Supernova Hawking, it adds abrasion protection to an already noble material. On gold, the application is rarer but exists: H. Moser & Cie. uses it on titanium inserts paired with rose gold cases, not on the gold itself.

A variant is colored DLC: Trilobe uses it in green and blue on titanium rings. It's obtained by modifying the process gas composition. Hardness is slightly lower than standard black DLC, but remains markedly superior to traditional colored PVD coatings.