Spectrophotometric Behaviors of Colorant Calcium Carbonate: A Study on Absorption, Reflection and Transmission

Abstract

In this present study, the optical properties such as absorbance, transmission, reflection, absorption coefficient, extinction coefficient, and refractive index of differently colored-green, blue, yellow, and white-CaCO₃ (chalk) are investigated. The absorbance spectra show that each color selectively absorbs certain wavelengths according to the Beer-Lambert Law, which states that absorbance is directly proportional to the concentration of the absorbing species, path length, and absorption coefficient. This relationship between color perception and selective wavelength absorption is further evidenced by the transmission and reflection spectra, whereas white CaCO₃ shows the most homogeneous reflection with quite low absorption. It has been revealed that the extinction and absorption coefficients show strong absorption and scattering in regions complementary to the colors observed, whereas the refractive index shows only slight variations due to structural or pigment-related differences. These findings should improve the knowledge concerning the optical behavior of colored CaCO₃ with applications that range from pigment formulation through material characterization up to optical coatings.