In message , oz writes
When a car is welded together, piece by piece, and gets ready for
>painting, the steel starts to oxidize (FeO)just sitting there. The
>body must be acid cleaned (ex: dipped in sulfuric acid) to clean off
>the oxidation just prior to painting.
Phosphoric acid is used, as Iron Phosphate bonds perfectly to iron and steel, as well as cleaning it. Sometimes Sulphuric acid is used to speed up the oxide etching process.