Ponceau 6R, or Crystal ponceau 6R, Crystal scarlet, Brilliant crystal scarlet 6R, Acid Red 44, or C.I. 16250, is a red azo dye. It is soluble in water and slightly soluble in ethanol. It is used as a food dye, with E number E126. It is also used in histology, for stainingfibrin with the MSB Trichrome stain. It usually comes as disodium salt.
Amaranth is a closely related azo dye, also usable in trichrome staining.
Its CAS number is 2766-77-0 and its SMILES structure is OC1=C(N=N C3=C(C=CC=C4) C4=CC=C3)C2=C (C=C(S(=O) ([O-])=O)C=C2 S(=O)([O-]) =O)C=C1.