Metal pickling and cleaning compounds are acid and alkaline solutions for removing scale, rust, and grease contamination prior to painting, galvanizing, soldering, and welding. Acid pickling agents: HCl (hydrochloric), H₂SO₄ (sulfuric), H₃PO₄ (phosphoric) with corrosion inhibitors and surfactants. Phosphating primers (Zn₃(PO₄)₂) simultaneously clean and create a conversion phosphate coating. Alkaline cleaners: NaOH, Na₂CO₃, surfactants for degreasing. Passivators (CrO₃, Cr-free based on Zr/Ti) provide final protection. Packaging: canisters 10–30 L, drums 200 L, IBC 1000 L. Documentation: safety data sheet (MSDS), quality protocol. Chrome-free passivation (Zr/Ti based) replaces chromating (CrO₃ is toxic, REACH Annex XIV). The conversion coating of 20–50 nm ensures paint adhesion and short-term corrosion protection. Documentation: MSDS, TDS, quality protocol.