Chromiferous azo dyes are made by treating in acid medium a mixture of one or more chromium compounds of azo dyes and one or more chromable azo dyes, the mixture containing at least one chromium compound of an azo dye of the general formula <FORM:0422605/IV/1> wherein the OH and the azo group are in o-position, R=a naphthol residue and the ring X of the naphthalene residue is unsubstituted, as well as at least one azo dye of the said general formula. In examples (1) the dye 1-amino-2-naphthol-4-sulphonic acid --> b - naphthol is treated with chromium formate, the chromium compound is suspended in water with the dye 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol and the mixture refluxed with acetic acid, (2) the chromium compound made in alkaline medium from the dye 1-amino-2-naphthol-4-sulphonic acid --> a -naphthol is heated with the unchromed azo-dye in presence of sulphuric acid, (3) the chromium compound of the dye 1-amino-2-naphthol-4-sulphonic acid --> a -naphthol is heated in acetic acid with the unchromed dye; (4) the mixed chromium compound obtained by treating with chromium formate equal parts of the dyestuffs 1-amino-2-naphthol-4-sulphonic acid --> a -naphthol and 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol are refluxed with the same unchromed azo dyes in presence of formic acid. Examples of the dyeing process are also given. Navy blue to black shades are obtained. The mixtures may contain mono-, dis- and polyazo dyes in which the coupling components may be amines, phenols, pyrazolones, oxyquinolines, barbituric acids, acetoacetic acid and benzoylacetic-o-carboxylic acid and derivatives thereof. The acid medium may be hydrochloric, sulphuric, formic, acetic, oxalic, propionic, benzene sulphonic, a naphthalene disulphonic acid, lactic, or tartaric acid with or without an organic solvent, e.g. alcohol. The treatment may occur in the dye-bath. Specifications 364,148, 384,767, and 408,497 are referred to. The Specification as open to inspection under Sect. 91 comprises also the following examples; (1) the chromium compound produced in alkaline medium from the dye 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol is heated with the unchromed dyestuff in presence of benzene sulphonic acid or tartaric acid; (2) the chromium compound obtained in alkaline medium from the azo dye 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol is refluxed with the azo dyes 1-amino-2-naphthol-4-sulphonic acid --> a -naphthol and 4-nitro 2-aminophenol-6-sulphonic acid --> acetic acid anilide in presence of tartaric acid; (3) the mixed complex chromium compound made in acid medium from the dyes 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol and nitrated 1-diazo-2-naphthol-4-sulphonic acid coupled with b -naphthol is refluxed with the dyestuff 1-amino-2-naphthol-4-sulphonic acid --> a -naphthol in presence of benzene sulphonic acid; (4) the mixed chromium compound of (3) is suspended in aqueous propionic acid and refluxed with the dyes 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol and 1-amino-2-naphthol-4-sulphonic acid --> 1-phenyl-3-methyl-5-pyrazolone; (5) the mixed chromium compound of (3) made with chromium formate is refluxed with the dyestuffs 1-amino-2-naphthol-4-sulphonic acid --> a -naphthol and 2-amino-1-phenol-4-methyl-5-sulphonic acid --> b -naphthol in presence of formic acid; (6) the chromium compound made in acid medium from the dyestuff 1-amino-2-naphthol-4-sulphonic acid --> b -naphthol is refluxed in presence of sulphuric acid with the dyestuffs 2 - amino - 1 - naphthol - 4 - sulphonic acid --> b -naphthol and 2-amino-4-sulphone-benzene carboxylic acid --> p 1-(2<1> methyl-4<1>-sulpho)-phenyl-3-methyl-5-pyrazolone. A table is also given of similar dyestuffs in which the following additional dyestuffs are mentioned as starting materials: 4-chloro-2-aminophenol --> 1 : 5-dioxynaphthalene, 1 - amino - 2 - naphthol - 6-o -sulphomethylamino - 6 - sulphonic acid --> b -naphthol, 4-chlor-2-aminophenol --> chromotropic acid, 4-sulpho-2-amino-1-benzoic acid --> 1-phenyl-3-methyl-5-pyrazolone, 4-chloro-2-aminophenol-5-sulphonic acid -->b -naphthol and 6-nitro-2-amino-1-naphthol-4-sulphonic acid --> a -naphthol. This subject-matter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specification 297,331, [Class 2 (iii)].