How can a layer of aluminium oxide on an aluminium object be made thicker? What is the process called?

Explanation

Aluminium develops a thin oxide layer whne 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. This process is called anodising.
During anodising, a clean aluminium article is made the anod and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts wiht aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.