Impact of Acacia and Tragacanth Gums on the Surface Characteristics of Traditional Wood-Supported Polychrome Paintings

Polychrome paintings on wooden artifacts are vital elements of cultural heritage, where plant-derived binders play a crucial role in color formation and durability. This study aims to systematically compare the chemical, optical, and surface characteristics of two traditional natural adhesives—acacia gum (AG) and tragacanth gum (TG)—to better understand their influence on the preservation and reproduction of wood-supported polychrome coatings. Fourier-transform infrared spectroscopy (FTIR) confirmed their polysaccharide-rich structures, with distinct ester and glycosidic linkages, while rheological tests demonstrated that TG exhibited higher viscosity at 1–3% concentrations, whereas AG showed a sharper increase at 5%, reflecting different molecular architectures. Colorimetric analysis combined with two-way ANOVA revealed that gum type significantly influenced color development in blue and red coatings (p < 0.001), while yellow and green coatings remained largely unaffected. Gum concentration (1–5%) generally showed no significant effect on color. All coatings exhibited a matte appearance (<3 GU), with statistical analysis indicating that gloss was mainly determined by pigment particle distribution rather than adhesive type. Surface roughness increased notably with gum concentration (p < 0.001), demonstrating that binder content strongly affects coating microtexture. Overall, pigment type was the dominant factor for color, whereas gum concentration critically influenced surface morphology. These findings provide practical guidance for optimizing natural adhesives in the conservation of traditional polychrome artifacts.