What greydog said. "Removal of rust is, generally speaking, a mechanical operation. "
Red rust is softer than black rust (bluing) so the red rust, if truly on the surface, will come off faster. Some lesser amount of black rust will come off too. Just keep that in mind when picking what to scrub with.
If you find a chemical that will remove red rust without affecting black rust let me know, we'll both make millions. Or convert red rust back to a smooth black rust for that matter. No, boiling water won't change it back to the smooth coating it once was.
