Surface treatments

ANODISING (OR ELOXAL PROCESS)

1. General description

This is a surface treatment specific to aluminium, to titanium, to tantalum and to their alloys. It is an electrolytic process, carried out in a sulphuric acid bath, which oxidises the surface of the metal. The surface oxide is harder than the substrate and gives it a stable and homogeneous appearance. When treating aluminium, pigments added to the bath make it possible to colour the aluminium oxide (alumina) and therefore the treated component. Titanium oxide, for its part, is coloured during electrolysis, depending on the intensity of the electric current, across a complete palette of colours. Since the titanium alloys used in watchmaking are stainless, anodised titanium is almost absent from it.

2. History

The anodising process and surface colouring of Aluminium using pigments were discovered in 1923. The process and the uniformity of the colours obtained have continued to improve since then, even though the principle and technology remain unchanged.

3. Advantages and disadvantages

Advantages

Hardening of the surface

Protection against deep corrosion

Colouring during treatment

Stable and uniform appearance

Disadvantages

Relatively limited Pallet stone of colours