Everything I learned about cleaning kettles, I learned from the experts on this site, so I don't have much to add except to say that 0000 steel wool is a polishing wonder for both porcelain and vent covers, and that automotive polishing compound (not wax!) from I think Turtle Wax is great stuff. Mother's magnesium and aluminum polish is awesome, too. But the main thing is lots of scrubbing with the 0000 steel wool. Be patient and persistent.