A copper complex formazan compound conforming to the formula (1) ##STR17## where A is a benzene or naphthalene ring, which is unsubstituted or substituted by substituents selected from the group consisting of halogen, nitro, alkyl of 1 to 5 carbons, alkoxy of 1 to 4 carbons, alkylsulfonyl of 1 to 4 carbons, phenylsulfonyl, sulfamoyl and N-monoalkyl- and N,N-dialkylsulfamoyl each of 1 to 4 carbons in the alkyl;
- B is a straight-chain or branched-chain alkylene of 1 to 8 carbons, or a straight-chain or branched-chain alkenylene of 2 to 8 carbons, which is unsubstituted or substituted by a phenyl which is unsubstituted or substituted by substituents selected from the group consisting of methyl, ethyl, methoxy, ethoxy, fluorine, bromine, chlorine and sulfamoyl, or is alkylene-phenylene having 1 to 4 carbons in the alkyl moiety or alkenylene-phenylene having 2 to 4 carbons in the alkenylene moiety, in each of which the phenylene is unsubstituted or substituted by substituents selected from the group consisting of methyl, ethyl, methoxy, ethoxy, fluorine, chlorine, bromine and sulfamoyl, or is phenylene or naphthylene, each being unsubstituted or substituted by substituents from the group consisting of hydroxy, nitro, halogen, alkyl of 1 to 5 carbons, alkoxy or 1 to 4 carbons and carbalkoxy having 1 to 4 carbons in the alkyl moiety, or is the bivalent radical of furan, thiophene, pyrrole, imidazole, indole, pyrazole, pyridine, pyrimidine, quinoline or benzimidazole, or
- --B--Z is together hydrogen;
- Z is sulfo or carboxy, attached as additional substituent on A and B to an aromatic of aliphatic carbon of A and B or to an aliphatic carbon of a substituent of A;
- k is 1 or 2;
- m is zero, 1 or 2 (if zero, Z being hydrogen);
- n is zero, 1 or 2 (if zero, Z being hydrogen);
- the sum (m+n) is from 1 to 4;
- if Z if present two or three times in the molecule, it may have different meanings within the stated meanings;
- X is oxygen of carbonyloxy of the formula --CO--O--, the group X and the N-atom being bonded ortho to each other to the aromatic nucleus of A;
- R is hydrogen or an unsubstituted or substituted alkyl of 1 to 4 carbons wherein the substituents are selected from the group consisting of hydroxy, carboxy, sulfato, phosphato, sulfo, cyano, alkoxy of 1 to 4 carbons, alkoxyalkoxy the alkyl and alkylene moieties of which being each of 1 to 4 carbons, and a group of the formula --SO.sub.x --Y, where Y is as defined below;
- D is an phenylene, unsubstituted or substituted by substituents selected from the group consisting of hydroxy, nitro, chlorine, bromine, fluorine, alkoxy of 1 to 4 carbons, alkyl of 1 to 4 carbons, sulfo, carboxy, .beta.-sulfatoethylthio, alkylamino and dialkylamino each of 1 to 4 carbons in the alkyl moiety or moieties where either or both of the alkyl groups in said alkylamino and dialkylamino are unsubstituted or substituted by hydroxy, sulfo, carboxy, sulfato, phosphato, alkoxy or 1 to 4 carbons, alkoxyalkoxy having 1 to 4 carbons in the alkyl or alkylene radical, hydroxyalkoxy of 1 to 4 carbons in the alkylene radical, sulfatoalkoxy of 1 to 4 carbons in the alkylene radical and succinylamido of the formula --NH--CO--CH.sub.2 --CH.sub.2 --COOM, where M is defined below;
- an unsubstituted or a sulfo-substituted naphthylene, alkylene of 1 to 8 carbons, alkylene of 2 to 8 carbons interrupted by 1 or more hetero moieties selected from a group consisting of --NH--, --N(R.sup.1)--, --O--, --S--, --SO.sub.2 --, --CO--, --SO.sub.2 --NH--, --NH--SO.sub.2 --, --CO--NH-- and --NH--CO--, or substituted by 1 or 2 substituents from the group consisting of hydroxy, sulfo, carboxy, sulfato, phosphato, and alkanoyloxy of 2 to 5 carbons, or alkylene of 2 to 8 carbons substituted by 1 or more said hetero moieties and hydroxy, sulfo, carboxy, sulfato, phosphato, and alkanoyloxy of 2 to 5 carbons, or
- D is a group of the general formula (2a), (2b), (2c), (2d), (2e), (2f), (2g) or (2h) ##STR18## R.sup.1 is hydrogen or alkyl or 1 to 4 carbons, R.sup.2 is hydrogen or alkyl of 1 to 4 carbons, which is unsubstituted or substituted by a group of the general formula --SO.sub.2 --Y, where Y is as defined hereinafter, or by carboxy, sulfato, methoxy, ethoxy or chlorine, or is phenyl which is unsubstituted or substituted by 1 or 2 substituents from the group consisting of methyl, methoxy, ethoxy, sulfo, carboxy and chlorine,
- G is phenyl which is unsubstituted or substituted by 1 or 2 substituents from the group consisting of chlorine, alkyl of 1 to 4 carbons, alkoxy or 1 to 4 carbons, hydroxy, sulfo and carboxy,
- arylene is phenylene which is unsubstituted or substituted by 1 or 2 substituents from the group consisting of chlorine, bromine, nitro, alkoxy or 1 to 4 carbons, alkyl or 1 to 4 carbons, carboxy and sulfo, or is naphthylene which is unsubstituted or substituted by 1 or 2 sulfo groups,
- alkylene is alkylene of 1 to 8 carbons, or is alkylene of 2 to 8 carbons, which is interrupted by 1 or more said hetero moieties or is substituted by 1 or 2 substituents from the group consisting of hydroxy, sulfo, carboxy, sulfato, phosphato and alkanoyloxy of 2 to 5 carbons, or is alkylene of 2 to 8 carbons substituted by 1 or more said hetero moieties and hydroxy, sulfo, carboxy, sulfato, phosphato, and alkanoxyloxy of 2 to 5 carbons, the alkylene and arylene moieties in the radicals of the general formulae (2d) to (2g) may in each case be separated from each other by one of the said hetero moieties;
- Y is vinyl or an ethyl which is substituted in the .beta.-position by a substituent which is eliminated under alkaline conditions;
- and
- M is hydrogen, an alkali metal, or one equivalent of calcium.