A method for forming a black-passivation layer on a zinc-iron alloy, the method comprising the steps: (a) providing a substrate comprising the zinc-iron alloy, (b) providing a black-passivation composition for depositing the black-passivation layer on the zinc-iron alloy, the composition comprising (i) one or more than one blackening agent selected from the group consisting of formula, wherein R 1 and R 2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and n is 1, 2, 3, 4, or 5, and formula, wherein R 4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and m is 1, 2, 3, 4, or 5, and (ii) one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, and (c) contacting the substrate with said black-passivation composition such that the black-passivation layer is formed on the zinc-iron alloy. (a) providing a substrate comprising the zinc-iron alloy, (b) providing a black-passivation composition for depositing the black-passivation layer on the zinc-iron alloy, the composition comprising (i) one or more than one blackening agent selected from the group consisting of formula, wherein R 1 and R 2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and n is 1, 2, 3, 4, or 5, and formula, wherein R 4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and m is 1, 2, 3, 4, or 5, and (ii) one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, and (i) one or more than one blackening agent selected from the group consisting of formula, wherein R 1 and R 2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and n is 1, 2, 3, 4, or 5, and formula, wherein R 4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and m is 1, 2, 3, 4, or 5, and formula, wherein R 1 and R 2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and n is 1, 2, 3, 4, or 5, R 1 and R 2 are independently selected from the group consisting of hydrogen and C1 to C5 alkyl, R 3 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and n is 1, 2, 3, 4, or 5, and formula, wherein R 4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and m is 1, 2, 3, 4, or 5, and R 4 is selected from the group consisting of sulfonic acid, carboxylic acid, alkyl carboxylic acid, phosphonic acid, salts and esters thereof, and m is 1, 2, 3, 4, or 5, and (ii) one or more than one species of metal ions selected from the group consisting of trivalent chromium, titanium, and zirconium, and (c) contacting the substrate with said black-passivation composition such that the black-passivation layer is formed on the zinc-iron alloy.