I have a 42 inch magnolia sign that has quite a bit of smoke soot and residue from a fire on one side. I need to know from experts what is the best method to remove it without damaging the porcelain finish. Thanks in advance for your advice.
I use "Mothers Mag Wheel polish" It won't damage the porcelain, no matter how hard you rub, and it will remove that type of stain fairly easy. It won't remove heat discoloration from the fire though! Nothing will!
Try Easy-Off oven cleaner. It's made to clean heat-enhanced nastiness off of porcelain without harm to the finish.
Don't ask me how I know.
Mr. Frith is right about the impossibility of removing some kinds of potential damage.