Describe the process of anodising. What is its purpose?

Anodising is an electrolytic process used to increase the thickness of the natural oxide layer on the surface of metal parts, typically aluminium. The aluminium article is made the anode and dipped in an electrolyte like dilute sulphuric acid. When current is passed, oxygen gas is evolved at the anode, which reacts with aluminium to form a thicker, stronger, and more corrosion-resistant aluminium oxide layer. The purpose of anodising is to protect the metal from corrosion, improve its wear resistance, and allow for decorative colouring.