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My name is Doug Otten and I run an electropolishing/passivating shop for stainless steel. At Complete Metal Finishing, Inc. we electropolish and passivate 200, 300, 400 series stainless and Hastelloy grades. A protective thin film oxide is created in passivation, which leaves the product with about the same brightness it had incoming. Electropolishing removes the peaks on the surface miroscopically and exposes a chrome rich surface, which tend to brighten if not make the surface like a mirror. The incoming surface finish is critical in electropolishing if a mirror finish is the desired result.

Anyway both processes clean the surface and really help stainless become stainless. The reason rust spots are somtimes found on stainless steel is because that is free iron not protected by the chromium.

Hope this helps,
Doug