a once popular way is with acid, sounds scary but its not, take muriatic [swimpool acid] break it down 10 0r 15 to 1 with water and throw it on or brush it on rinse it immediately, it will remove oxidation leave it looking kinda white, if your gonna polish it polish it right away don't wait, this can make polishing aluminum easier as you don't have too rub thru the oxidation. experiment with a weak mixture, too strong and it will etch the aluminum. I had a trucking business and used to polish my heart away, some guys with very highly polished trucks would do exactly this to make it happen faster. Call a truck wash and ask them if they acid wash or have hotsoap or aluminum brightener. too hot an acid or too much acid washing with out ever polishing and the surface gets pourous looking. be carful watch what you splash when working and when the acid is full strength it will mess you up bad. it wont eat that plastic bottle it comes in but it will eat most everything else.