Stainless steel is not just one material: it's a family, and anyone who works at the bench knows this from the start. The most common grade in series watchmaking is 316L, with nickel and molybdenum in moderate percentages. Rolex and some other manufacturers use 904L, an alloy with higher levels of nickel and molybdenum, more resistant to marine corrosion and capable of holding its polish longer over time. You can feel the difference on the stone and the flannel wheel.
Over the last twenty years, brands have developed proprietary alloys to stand out. Grand Seiko calls theirs Ever-Brilliant Steel: compared to standard stainless, it reflects more uniformly and resists corrosion better. Omega has O-MEGASTEEL, with 40% higher hardness than conventional steel, hypoallergenic and anti-magnetic, visually brighter. Chopard works with Lucent Steel A223, which uses 85% recycled material and alternates polished and satin finishes. None of these brands have yet published their exact composition: they evaluate themselves on practical results, not technical data sheets.
Damascus steel is a chapter apart. It's obtained by layering and forging two different types of steel, then cutting, recombining, reforging and etching with acid to reveal the pattern. Houses like GoS use it for dials and cases: each piece has a unique design. The so-called bonded patina is a variant where the dark surface is structurally integrated into the material, not applied on top, and resists ordinary wear.
The steel-precious metal combination has a long tradition. Rolex calls Rolesor the combination of Oystersteel with yellow, white or Everose gold, the latter introduced in 2005 as a proprietary rose alloy. Rolesium instead indicates the Oystersteel-platinum pairing. Jaeger-LeCoultre was already using two-tone in the 1930s Reverso: a steel case with gold elements, more robust than a piece entirely in precious metal.
Surface coatings add another variable. DLC (Diamond-Like Carbon) is a very thin, extremely hard, black layer that reduces scratches and wear on bezels, crowns and casebacks. Cerasteel by Bangalore Watch Company combines a steel structure with a ceramic coating. In both cases the substrate remains steel: mechanical resistance comes from the core, not from the coating.
On the thermal side, annealing is the treatment that reduces internal stresses in cold-worked steel, making it more stable. It's applied to thin hands, those of 0.2 mm, which might otherwise curve over time. Hot bluing of hands is a different process: controlled surface oxidation, color as a result, no significant structural change.