Use of compositions containing bisazo compounds for detecting fissures

A method of using compositions comprising as components

• A) at least one bisazo compound selected from the group consisting of the compounds of the general formula Ia
• and of the general formula Ib
• where
• R1 is C-C8-alkyl,
• R2 is C2-C8-alkyl,
• R3 and R3′ are each C2-C21-alkyl in which up to four CH2 groups of the carbon chain may be replaced by oxygen in ether function,
• R4 is independently of R3 hydrogen or C2-C21-alkyl in which up to four CH2 groups of the carbon chain may be replaced by oxygen in ether function,
• R4′ is independently of R3′ hydrogen or C2-C21-alkyl in which up to four CH2 groups of the carbon chain may be replaced by oxygen in ether function, and
• B) at least one solvent in which said component A) is soluble;
• as dye penetrants for detecting surface cracks or other defects in workpieces to be tested in this respect.