anodizing

The Occhio surfaces are gold matt and some of the chrome matt surfaces are anodized. In the following, this method will be briefly described.

The anodizing process (from Eloxal, abbreviation for electrolytic oxidation of aluminum) is a surface technique for producing an oxide protective layer on aluminum by anodic oxidation. In this case, in contrast to the galvanic coating method such as the PVD coating, the protective layer is not precipitated on the workpiece, but formed by conversion of the uppermost metal layer, an oxide or hydroxide. The result is a 5 to 25 micron thin layer, which protects against corrosion - the natural oxide layer of aluminum is only a few nm. 

First, the aluminum parts are pretreated, i.e. cleaned and degreased and pickled to remove the thin natural oxide layer of aluminum.

After the surface pre-treatment, the actual anodizing takes place:

In a sulfuric or oxalic acid bath, a metal is electrolytically "dissolved" by means of electricity and then settles on the aluminum.

The electrolytic dyeing is carried out with AC voltage. The electrolyte contains a coloring metal salt. The duration of the electrolysis depends on the desired color depth. The metal ions penetrate deeply into the pores of the layer. The pores, which are partly filled with metal, now cause a lightfast coloration due to their absorption and scattering effects.