A common requirement for laser marking is to achieve a high optical contrast without the surface being mechanically damaged by the laser. These criteria are particularly important for laser marking in the food industry and in medical technology. However, this is also a frequent requirement for rotationally symmetrical bodies, as marking or engraving would change the mass moment of inertia and permanent concentricity could not be guaranteed.
The solution to this is a special marking process known as black marking. In black marking, the laser heats the material surface (anodized layer) and the volume underneath. The metal grid is vibrated by the laser so that the carbon trapped in the structure can diffuse to the surface. This deposition is then perceived as an inscription. The inscription appears black.