Aluminum stained black after being machined

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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Try an agressive solvent like lacquer thinner. If that didn't work, I would try phosphoric acid. You can get it at an automotive paint store. It is the chemical used to prep aluminum for the chem-film (alodine) process.
Jerry
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