I have a bench grinder just for that stuff.

One side has a soft wire wheel, will take the oxidized aluminum off without removing much good aluminum. The other side has a cloth wheel, I use rouge on the cloth side, get a mirror finish. If I do it right, it is brighter than chrome and I can see myself.

Be careful with sandpaper on cast aluminum. Castings usually have a smooth skin with more porous metal underneath. If you buff through the skin you will end up with a pinhole mess that will never polish up well.

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Gone to the dark side

- Jeff