Painted aluminium surfaces can oxidise, particularly if moisture manages to seep in between the paint and the aluminium. Removing the oxidation is nearly impossible without also removing the paint around it. The best way to remove oxidation from painted aluminium is to strip the paint, polish the metal, then repaint the aluminium. This method will restore the integrity of the aluminium and the paint. Work in a well-ventilated area and avoid inhaling chemical fumes.
Pour chemical paint stripper recommended for use on aluminium onto a rag. Use the rag to spread the stripper onto the surface of the metal. Allow the stripper to sit for about 10 minutes, and then wipe away the paint. Rinse the aluminium with water and dry with a towel.
Spray the aluminium with oven cleaner. Allow the cleaner to sit for about 10 minutes. Put on rubber gloves. Rub the cleaner into the metal with steel wool. Rinse the metal with clean water and dry with a towel.
Rub some rough-grit polishing compound onto a buffing cloth. Attach the cloth to a polishing wheel. Polish the surface of the metal for about 30 seconds per section. Rinse the metal with water and dry with a towel.
Repaint the surface of the metal using spray paint or other paint designed for use on aluminium.
Sand-blasting will also remove paint and oxidation from aluminium.
Do not inhale fumes from paint stripper and oven cleaner. Use extra care when refinishing aluminium window frames. Chemicals and polishing compound could scratch glass or plexiglass.