Guys guys GUYS !!
I am a pharmacist by profession. The thought of using Oxalic acid makes me shiver ! This stuff is NOT nice and needs to be treated carefully. You also have to dispose of it carefully as it should NOT be disposed of into the normal sewer system. You don't want it on your skin, in your eyes or on your clothes and you definitely do NOT want to inhale the fumes/mist !!! It will eat you from the inside out.
May I suggest that if you don't like using it, or have had no experience of handling it, using Hammerite Rust Remover (Dip) is far safer and the results are as good. You can get it from any good car spares place (I get mine from Halfords). Read the instructions carefully and follow them.....it's good stuff.
Just be aware you need to regularly check any item being dipped.....the stuff is so strong I have learned the hard way and lost a relic when i first used it !! The relic was far more corroded than i thought and the remover did eat the corrosion.....but left me with a sliver of metal !!!!! Ate the whole bloody relic !!
....but if you're careful it is great stuff.