Abstract: A method is described for preparing a black chromium-containing conversion coating on a zinc-nickel alloy surface containing at least about 8% nickel in the alloy or on a zinc-iron alloy surface. The method of the invention comprises contacting said surfaces with an aqueous acidic solution comprising trivalent chromium and an amount of a phosphorus acid selected from phosphoric acid, phosphorous acid, hypophosphorous acid, and mixtures thereof effective to provide a solution having a pH of from about 1.0 to about 2.5. Metal articles having zinc-nickel alloy surfaces containing at least about 8 % nickel in the alloy or having zinc-iron alloy surfaces which have been treated in accordance with the method of the invention exhibit the desired blackened surfaces and are characterized by improved corrosion resistance.

Abstract: It now has been found that a smooth, level, matte and/or bright deposit of tin, lead or tin-lead alloy can be deposited on a substrate from an aqueous plating bath which comprises(A) at least one bath-soluble metal salt selected from the group consisting of a stannous salt, a lead salt, or a mixture of stannous and lead salts; and(B) at least one alpha-acetylenic alcohol or glycol of the formulaR.sub.1 R.sub.2 C(OH)C.tbd.CR.sub.3 (I)whereinR.sub.1 and R.sub.2 are each independently H, an alkyl group, a cycloalkyl group or R.sub.1 and R.sub.2 together with the carbon atom form a cyclic group, provided that at least one of R.sub.1 and R.sub.2 is an alkyl group containing at least three carbon atoms, andR.sub.3 is H, an alkyl group or --C(OH)R.sub.1 R.sub.2.Preferably the plating baths do not contain fluoride or fluoborate ions, and the baths are also free of strong inorganic acids such as sulfuric acid.