Thank you both for your input. I should have been more specific, however; this is old, very inactive rust (brown-black, in fact) which is pretty hard to get rid of. The active stuff I've already dealt with; it's this hideously ugly, but nonetheless fairly innocuous, black patchwork that I'd like to combat if I can. The problem is, of course, that it's very firmly bonded to the steel. Mechanical means seem difficult to pursue as a result, and chemical treatments have the potential to go very badly awry, hence my concern over whether to proceed. I can try applying de-corroding chemical treatment, for instance, but I do worry about it destroying the pattern. Alternatively, I can try using a brass pick and oil and a lot of patience, which should leave a surface that can be etched - in about six months.
