An aqueous composition including (a) metal ions including tin ions and silver ions and (b) at least one complexing agent of formula C11
R.sup.C12-X.sup.C11-R.sup.C11 (C11)
and their salts, where X.sup.C11 is selected from (a) a divalent 5 or 6 membered aromatic N-heterocyclic group; (b) a divalent 6 membered aromatic carbocyclic group; and (c) a divalent 5 or 6 membered aliphatic N-heterocyclic group including one N atom and optionally a second heteroatom selected from N and O; all of which may be unsubstituted or substituted by one or more OH or one or more R.sup.C14; R.sup.C11 is selected from ##STR00001## ; and R.sup.C12 is selected from R.sup.C11, X.sup.C11-R.sup.C11, H, OH, NR.sup.C14.sub.2, C.sub.1 to C.sub.10 alkyl, and C.sub.1 to C.sub.10 alkoxy