MULTI-ANGLE COLOUR CHARACTERIZATION OF COATINGS WITH DIFFRACTION PIGMENTS (OP10, Pages 51-59)

The reflectance properties of coatings with effect pigments result in a quite strange colour sensation for humans. The colour of effect pigments is caused by anisotropic optical processes like low-order scattering, interference, or diffraction. This work specifically deals with the reflectance characterization of effect coatings with diffraction pigments. Its main purpose is to determine the most adequate illumination/observation geometries to characterize the variation of its colour gamut. We propose a relevant geometrical variable to study the spectral reflectance and colour variation of coatings with diffraction pigments. At fixed values of this geometrical variable, the component of the spectral BRDF due to diffraction is almost constant. Based on the spectral BRDF of six coatings, which were measured by the robot-based goniospectrophotometer available at IO-CSIC, we show how the spectral BRDF can be represented by basic functions, which depend on either the wavelength or on the proposed geometrical variable. Finally, the chromatic analysis of the studied coatings was discussed.