Annealing marking is a method that is exclusively limited to metals - more precisely, alloys with iron and at least low carbon content. Here, the action of heat and oxygen and diffusion of the alloy components changes the color of metal in the top layer. The laser-induced temperature is typically in the range of 220°C – 500°C, it remains below the melting temperature of the alloy. Annealing colors are found in everyday life e.g. in exhaust manifolds on motorbikes, which are often stained golden-violet. The process of staining is the same as the typical temperature of the exhaust gases of a four-stroke engine is around 300°C.
The big advantage of this method is that no material removal takes place. I.e. the mechanical integrity and, to a large extent, the chemical properties (e.g. rust-inhibiting) are retained. At the same time, however, the marking is also extremely durable, as long as the component does not reach the aforementioned temperatures in later use.