Dyeing anodized aluminum with cobaltiferous azo-dyestuffs

The invention comprises complex cobalt compounds containing one atom of metal bound to two molecules of the same monoazo-dye or to one molecule each of two different monoazo-dyes, which dye, or dyes, contain SO3H groups and are of formula R-N=N-A-Y where R is a hydroxy benzene residue, containing a nitro group, bound to N2 #s to the OH group, A is a naphthylamine residue with Y, an at most secondary amino group, vicinal to N2. The dyes are made in conventional fashion by metallizing dyes made from appropriate phenolic diazo, and naphthylamine coupling, components. They may also be made by metallizing corresponding #s-alkoxy- or -acyloxy- #s1-amino-dyes. Typical of amines specified for use as diazo components are:-4-nitro- 2-aminophenol- 4- and -6-sulphonic acids, 4-nitro-, 4-chloro- and -methyl- 5-nitro-, 6-nitro- 4-acetylamino- and 4, 6-dinitro- 2-aminophenols. Typical of specified coupling components are:-6-bromo-, -methyl- and -methoxy- 2-naphthylamines, 2-naphthylamine, 2-phenylaminonaphthalene- 21-sulphonic acid, 1-naphthylamine- 4- and 2-naphthylamine- 6-mono- and -3, 6-disulphonic acids. Metallization is preferably effected in an alkaline medium with salts in which the metal is a cation. The dyes are used especially for colouring anodically oxidized aluminium or alloys thereof from an aqueous bath. Examples are provided of the preparation of the complexes and their use in dyeing aluminium in black or greenish-black shades.