Optical properties of spherical and nonabsorbing styrene- acryl copolymer pigment spheres with concentric spherical shells were studied by wavelength-dependent reflectance from the slurry. The data were analyzed using a light-scattering model and Wiener bounds. The object was to obtain estimates for the refractive index of a particle shell as a function of wavelength.
Jääskeläinen, A., Peiponen, K-E., Richard, O., Tapper, U., Kauppinen, E., & Lumme, K. (2000). Estimation of the refractive index of plastic pigments by Wiener bounds. Optical Engineering, 39(11), 2959 - 2963. https://doi.org/10.1117/1.1313767