I find that if you polish with WD40, you get a quicker bite and a better result in fewer passes than if you polish dry. The dry polished bbls will be mirror-like, and I think this burnishing effect actually protects the metal (or perhaps the satin finish you get from polishing with oil helps retain more acid).

Of course, the other variables (strength of solution, temp, humidity, time etc.) all interact so you may not get the same result unless all the variables are the same.

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