THE ANODISING PROCESS

Chemical cleaning and etching This part of the process cleans the surface of the metal and etches it to give the matt finish typical of anodised aluminium. This surface finish is seen through the transparent anodic film.
Anodising The oxide film is grown by immersing the aluminium in a bath of dilute sulphuric acid and passing a current of approximately 150 amps per square metre (at approximately 20 volts) between the aluminium (the anode) and the cathode. The film produced is porous, hard, transparent and can be coloured in various ways
Colouring As the film is porous and transparent it can be coloured either electrolytically by deposition of metals near the base of the film or by absorption of organic dyestuffs into the film. More - link to products
Sealing The final stage is controlled hydration in boiling water which seals the pores and establishes the corrosion resistance of the film.