Primarily Petroliana Shop Talk Forums Shop Talk Petroliana Forums General Petroliana Discussion Cleaning rust that is 'on top' of porcelain

I wash to get all the crud possible off and spray the "clean" surface with muriatic acid, leaving it on several minutes. It is not going to hurt the porcelain. I then scrub good with Barkeepers Friend, sometimes with the acid still on the sign if it needs it. Always use gloves and do not breathe the fumes from the acid-not even a little bit.