The invention provides a composition for addition to water to provide an aqueous solution that is effective for use in the physico-chemical refinement of magnetic stainless steel surfaces said composition comprising, in a major amount, an acid ingredient consisting at least predominantly of oxalic acid and, in a minor amount, an accelerating ingredient consisting essentially of a sulfur-­containing compound such as a thiocyanate salt; and a nitrobenzene compound oxidising agent such as m-nitrobenzene sulfonic acid, said composition being at least substantially completely soluble in water at 20° Centrigrade, in amounts of said composition of up to 10 percent by weight of water. Advantageously the compositions can contain a hydroxyalkylamine surfactant containing 2 to 4 carbon atoms and a poly(oxyethylene)alkyl alcohol surfactant. Also provided are solutions containing the said compositions and processes for refining magnetic stainless steel surfaces using such solutions.