Fig. 1From: The synthesis characterization of historical novel azo pigments: implications for conservation scienceStructure of Historical Naphthol AS synthesized: PR7: R1 = R5 = –CH3, R3 = R7 = –Cl; PR10: R1 = R4 = –Cl, R7 = –CH3; PR11: R1 = R5 = –CH3 R4 = R8 = –Cl; PR18: R1 = R6 = –NO2, R3 = –CH3; PR19: R1 = –OCH3, R3 = –NO2, R5 = –CH3Back to article page