Anodising is an electrochemical process used to produce durable and decorative finishes. With the addition of dyes, this can also be done in a range of colours. The natural protective oxide coating formed on exposure of aluminium to the atmosphere can be thickened by anodising.
In essence, the process consists of passing an electric current through an acid solution in which the immersed aluminium component acts as the anode, and aluminium or lead typically provides the cathode.
During the process, electrolysis breaks down the water into oxygen and hydrogen; the oxygen combines with the aluminium to produce aluminium oxide and the hydrogen is liberated.