Aluminium can become scratched and dull over time. No matter where you find aluminium -- on boats, cars, trucks, motorcycle rims or anywhere else -- scratching and dulling are bound to happen. Keeping aluminium free of scratches takes a bit of elbow grease and a few common hand tools. When repairing scratched aluminium, exercise caution so that you don't damage the metal itself or create new scratches.
Clean the surface of the aluminium with dish soap and warm water, using a clean cloth. Rinse with water and dry with a towel. Rinse out the bucket and refill with fresh water.
Dip 400-grit sandpaper into the water, lightly dampening it. Begin to sand away the scratch in a gentle, circular pattern, not pressing down. This will begin to "erase" the scratch. Continue to dampen the sandpaper as necessary, then wipe dry with a towel to remove all dust.
Refresh the water in the bucket by pouring out the old water and refilling the bucket. Lightly moisten the 600-grit sandpaper using the fresh water and continue sanding the scratch on the aluminium with gentle, circular strokes. This will remove the scratch. Re-wet the sandpaper as needed.
Rinse the bucket and refill. Sand the scratch with dampened 1200-grit sandpaper but do not sand in a circular motion. Instead, sand gently in one direction only. This will finish the aluminium. Wipe dry with a towel.
Apply a thin, even layer of aluminium polish with a brush or cloth. Dry as long as suggested by the manufacturer. Polish with a microfiber cloth to make the aluminium shine.