Aluminium surfaces are often 'anodized'. This means the deposition of a layer of

1. Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. 2. For aluminium surfaces, anodizing involves passing an electric current through an acidic electrolyte bath with the aluminium part serving as the anode. 3. This process results in the deposition (or rather, formation and thickening) of a layer of aluminium oxide (Al2O3) on the surface. 4. This oxide layer is hard, corrosion-resistant, and can be dyed.