Abstract: An azo dye having the formula (1): ##STR1## wherein R.sup.1 represents hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, hydroxyalkyl, alkoxyalkyl, alkoxycarbonylalkyl, acyloxyalkyl, acylalkyl, hydroxyalkylaminoalkyl, cyanoalkyl, aminoalkyl, N,N-dialkylaminoalkyl, alkylaminoalkyl, chloroalkyl, bromoalkyl, carboxyalkyl, morpholinoalkyl, cyclohexyl, phenethyl, benzyl, phenyl, chlorophenyl, methoxyphenyl, nitrophenyl, tolyl, xylyl, dialkylaminophenyl and alkyl containing an ammonium group wherein the ammonium nitrogen is quaternized by alkyl groups or by an amino group with alkyl groups, or wherein the ammonium nitrogen atom is the heterocyclic nitrogen atom of a morpholine ring or a pyridine ring, wherein R.sup.2, R.sup.3, R.sup.4 and R.sup.5 represent hydrogen, chlorine, bromine, nitro, cyano, carboxyl, methyl, ethyl, propyl, butyl, trifluoromethyl, .beta.