ANODIZING
Anodic oxidation is a surface treatment specific to aluminium, titanium, and their alloys. It is an electrolytic process carried out in a sulphuric acid bath that oxidises the surface of the metal. The surface oxide is harder than the substrate and gives it a stable and homogeneous appearance. During the treatment of aluminium, pigments are added to the bath to colour the aluminium oxide (alumina) and therefore the treated component. During electrolysis titanium oxide changes colour depending on the intensity of the electric current, resulting in a full range of hues. The titanium alloys used in watchmaking are stainless, making anodised titanium virtually absent.
Anodization and colouring of aluminium surfaces with pigments were invented in 1923. The process and the homogeneity of the obtained hues have continuously improved, although the principle and technology have remained unchanged.
Advantages:
- Surface hardening
- Protection against deep corrosion
- Colouration during treatment
- Stable and uniform appearance
Disadvantages:
- Relatively limited range of colours