6-Amino-5-[(4-amino-2-sodiosulfophenyl)azo]-7-[[4-[(2,4-diaminophenyl)azo]-3,3-dimethoxy[1,1-biphenyl]-4-yl]azo]-1,8-dihydroxy[2,2-azobisnaphthalene]-3,6-disulfonic acid disodium salt