Thought I'd pass this along. I got this sign thrown in on deal for free. It was pretty rough but hey, it was free. I figure I had nothing to loose.
I reread some threads on rust stains and for some reason thought this may work... And lo and behold it did!
It sure did a good job...I didn't leave it on the surface long. And I did not see any loss in porcelain shine...however the shine that I started with was minimal from the onset.
Here you can see how rust cleared away from the worst spot.
I used some acrylic for the touch-ups... I am no painter. I am happy with the overall results.