Aluminium is a metallic material used to make items ranging from automobile trim to window frames. While it is more rust resistant than steel, aluminium will corrode over time when exposed to rain and other exterior elements. To improve its durability and help improve corrosion resistance, aluminium is often anodised before it is used in outdoor applications. Anodising is a complex process in which the metal is etched with acid and subject to electroplating. To clean and polish an anodised object, you must first remove the anodised coating.
Protect yourself as you complete this task. Wear safety glasses, and work in a well-ventilated area when dealing with these chemicals. Wear rubber gloves to protect your hands as your work.
Mix dry powdered sodium hydroxide with water in a large bowl or bucket. Use one tbsp of sodium hydroxide for every gallon of water. Make sure you have enough of this mixture to completely submerge the item you are cleaning.
Soak the anodised aluminium in the sodium hydroxide solution. This material will de-anodise the aluminium so it can be cleaned and polished.
Remove the item from the solution once a minute, and scrub the surface with a stiff brush. The sodium hydroxide will react with the coating on the aluminium to produce a filmy material. Brush this material away often so the hydroxide can continue to clean the surface.
Take the item out of the bowl or bucket, and rinse it clean with cold water. Dry it completely with a clean rag.
Sand the item with a very fine-grit sandpaper to remove scratches and other marks from the surface. Look for a paper that's 800 grit or higher.
Wipe the item clean with a dry rag to remove sanding dust, and sand it again with an even finer grit. Try 1200-grit paper, and sand until all scratches and marks are gone. Clean away sanding dust with a dry cloth.
Apply aluminium polish to the object using a polishing cloth. This cloth is designed to be lint free, which will provide cleaner results. Buff the object with this cloth to bring out the natural shine in the aluminium.
For items and surfaces not easily soaked, the Aluminum Anodizers Council suggests cleaning them with an abrasive sponge and very mild dish washing liquid.