The aluminium is anodised by the passing of an electrical current from the anode to the cathode. The item to be anodised becomes the anode part of the electrical circuit whilst the cathodes are already in the anodising tank. The electrical current causes oxygen to be released at the anode which combines with the aluminium to form the aluminium oxide which is the anodic film. The depth of the anodic film is determined by the time in the anodising tank, usually between 15 to 60 minutes which will create an anodic film thickness of between 5 and 25 microns.

The quality of the anodic film is determined by the temperature and concentration of the electrolyte and the current density applied. The anodic film is of a very porous honeycomb structure and must then be sealed in order to achieve the desired weather resistant properties. The film produced is porous, hard, transparent and can be coloured in various ways.

Colouring methods