A long long time ago, as a 16y/o, I worked in a sheetmetal shop. They showed me a bunch of artsy steel plate thing-a-majobbers, a brush, and some nasty chemicals of some sort; and said "start painting."
So, now, when I see that type of finish (all over the place) I remember that day. eesh
I dunno, maybe it doesn't passivate enough. (how much is that anyway?. . . I mean even indoors . .. Mild steel!? Was the "artist" thinking it would go into a zero humidity room somewhere? Seriously; this "artist" should stay in the macorroni camp. . ...this shouldn't be your problem. Hell, this problem isn't even defined. )