Stained aluminum

I have some parts which were machined and cooled with an un-known lubricant. They've got black stains on them, and in some cases a
powdery residue. Is there a simple/inexpensive way I can clean them?
Thanks, John
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sunshine-x wrote:

The residue may be from exposure to water. If they haven't been anodized you could use Scotch-Brite pads. Randy
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Dice Randy Replogle :

It seems a good idea
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