One of the advantages of making things from aluminium is that it can be Anodised to protect it from corrosion,to enhance its appearance and to make the surface resistant to marking and scratching.
Although the anodising process has similarities with electroplating,nothing is deposited on the Aluminium.Instead the surface is artificially oxidised (anodic oxidisation - “anodise”).The surface film produced,although thin(5 to 20 microns), is very hard (Aluminium Oxide is commonly used as an abrasive) and cannot flake or peel off.It also has the ability to absorb dyes which enables coloured finishes to be produced.
Commonly used colours are blue,red,black and gold.Green,purple and bronze can also be produced - and of course “silver” or natural (undyed).
Pre-polishing,etching or “brightening” will give shiny,matt or satin finishes.
The type of alloy will also affect the finish.Stronger alloys(with more “impurities”) generally become duller than softer,purer ones.Castings often go grey.