I have also used muratic acid with success. Never any ghosting or gloss fading. I don't recommend someone use acid on darker colored porcelain until they have some experience using it. I have also used bar keepers friend and think it does a good job. But, nothing has worked better and been easier than IronX. Quality of cleanliness is equal to Muratic acid. Level of effort, is almost zero. Acid you have to be quick, do some scrubbing, be extremely careful, have the water on stand bye, and not let it get on anything. It takes me 20 minutes to get ready for 5 minutes of work. Iron X, just spray on, wait 10 minutes, wipe it off with a sponge, and then hose off the sign. I have never encountered rust stains that I couldn't get off with acid or IronX. Sometimes I may have to use a light grade of steel wool like you have in your kitchen for tougher rust spots. Muratic Acid or Hydrochloric acid is sold to every car wash in the country. When used properly, it should never take the shine or dull the color on anything.
