What is anodising?
First, an oxidation layer is formed using an electro-chemical process in a bath containing diluted sulphuric acid. The aluminium surface is converted into a layer of aluminium oxide with a thickness of 5 to 25 microns (one micron is one thousandth of a millimetre). As opposed to other surface treatments, anodising does not apply a layer to the aluminium, but instead a layer is created within the aluminium itself. An advantage of anodisation over a varnish finish is that it retains the beautiful metal-look of the aluminium.
The main purpose of anodising is to protect the aluminium against corrosion. A secondary benefit is that anodisation can enhance the look of the aluminium through pre-treatment and/or colouring.