Goniospectrometric space curve for coatings with special effect pigments.

Advanced application of eye-catching effects occurring in coatings with special effect pigments requires controlling their appearance. For this purpose, angular dependent reflectance must be analyzed in terms of the used flakes and their distribution inside the coating; it is important to know the size of the surface area they cover, and the position and precision of their orientation. These properties were varied using our numerical model, which gave an angular dependent reflectance factor for each set of coating parameters. The method was applied to analyze how well the calculated goniometric reflectance factor could characterize the appearance of effect coatings. For this purpose, the spectra were transformed in the goniospectrometric space, and the obtained curve was analyzed. While its shape, position, and orientation in the space reveal the optical makeup of the coating, the goniospectrometric space curve could serve as an appearance fingerprint of the corresponding sample. The applicability of the theoretical predictions was confirmed using a coating with metallic flakes and one with mica-based Fe2O3 coated flakes.