Optical characterization of three red pigments, two organic and one inorganic, was studied in order to provide important and reliable parameters for research and applications. The pigments were C.I. Pigment Red 176, C.I. Pigment Red 57:1, and C.I. Pigment Red 101. All three pigments were used in their transparent form, that is, their radius of gyration was smaller than 250 nm. The particles were suspended in an apolar solvent and absorption, reflection, and scattering of the suspensions were measured by means of a single spectrophotometer and the effective complex refractive index was determined.
Jana Heuer, Ilpo Niskanen, Susanne Klein, and Kai-Erik Peiponen, "Optical Properties of Suspensions of Organic and Inorganic Red Pigments," Appl. Spectrosc. 65, 1181-1186 (2011)