In watchmaking, the term "carbon" groups together at least three distinct things, and confusing them is an error I see often even in press releases. The first is traditional carbon fiber, woven into sheets with the typical 45° crosshatch pattern. The second is forged carbon. The third is DLC, Diamond-Like Carbon, which is not a structural material but a coating.
Forged carbon is obtained by cutting short carbon fibers, arranging them randomly inside a mold, compressing them, and injecting resin. The pressing occurs under heat. The result is a composite with an irregular weave, not repeatable from piece to piece, which makes it visually different from classic weave. Artya also uses it in vivid colors — blue, orange, red — precisely because the resin matrix can be pigmented. The specific weight is low, impact resistance is good, but there is a practical limit: forged carbon cannot withstand threads. For this reason, when used for the case, the threaded ring for the caseback or bezel almost always remains in steel or titanium. Tissot with the PRX Forged Carbon solved it this way: the central cylinder that houses the movement, the caseback, and the crystal are in PVD steel, while mid-case and outer bezel are in composite. Richard Mille with Carbon TPT instead works on oriented layers, patenting a process different from forged: parallel fibers, inclined layers, more controlled structure.
DLC is another story. It is an extremely thin coating — on the order of microns — deposited in vapor phase on steel or titanium. Surface hardness is very high, superior to untreated steel. It absorbs light more than it reflects it, which explains the matte or anthracite look seen on many sports watches. It can be glossy or brushed depending on the finish of the substrate: DLC replicates the texture of the underlying metal, it does not transform it. It is applied to case, bezel, crown, caseback, buckle. It is not eternal: on sharp edges and friction areas it wears, and once scratched it cannot be repaired invisibly as one would do with steel polishing.
From the bench I add one thing: colored DLC — green, blue — exists, but stability over time is inferior to classic black. Before buying a watch with colored DLC, it is worth asking the brand what type of process they use and if they guarantee coverage in case of delamination.