I tried the BKF with a mild scuff pad with no luck. Left it on for about a minute and then cleaned it off- After it dried all the stains came back- Unless I am missing something?
It is a porcelain sign
BKF is a very weak solution, I'd think the rust is too heavy for that. Muriatic acid is an option, but it's very strong, and oxalic acid works, but even with that, you would need to keep it wet for a couple of days. The only think I don't know about is whether it would affect the porcelain finish. It would be good to do a little experimenting first. I order oxalic acid from a veterinary supply (Van Dyke) and use it to remove rust on antique auto parts. It works great, but use with gloves and safety glasses and use it outside.
