Did some research on the old "how to clean porcelain" topic. I have a Gulf Diesel sign that has light brownish staining through out the sign, tried WD40, Soft Scrub, toilet bowl cleaner and naval jelly..nothing will take it out. The navel jelly takes the brown out slightly. It appears that the staining is on top of the porcelain, but no luck. Like I said some stains........
