Anodising is a process of forming a thick oxide layer of aluminium.
Aluminium develops a thin oxide layer of aluminium oxide when exposed to air. This aluminium oxide coat makes it resistant to further corrosion.
The resistance can be improved further by making the oxide layer thicker.
During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can
be dyed easily to give aluminium articles an attractive finish.