The impact of measurement geometry on colorimetric properties of coatings based on cellulose nanocrystals (CNCs) and pearl luster pigments

This study investigates colorimetric behaviour of sustainable coatings fabricated using cellulose nanocrystals (CNCs) as a biopolymeric binder and different types of pearl luster pigments, which differ in chemical composition, pigment color, and particle size. Coatings that combine high-performance CNCs with pearl luster pigments, which impart angle-dependent color (iridescence) due to their optically thin layers, offer a unique optical effect driven by the interplay of structural color and pigment-based reflection. The black paper was double coated in machine direction using K Control Coater. Colorimetric values (CIELAB) and spectral reflectance (R%) of the coating were measured across the visible spectrum from 400 to 700 nm, with a fixed illumination angle of 45° and viewing angles of -15°, 15°, 25°, 45°, 75°, and 110°. Results reveal pronounced shifts in reflectance intensity and CIELAB values with changing viewing angle, driven by the type of pearl luster pigments and their orientation. The findings provide insight into the design of sustainable, visually dynamic coatings for decorative and functional applications, where controlled angular color variation is desirable.