Mechanisms of Surface Deposition-Induced Optical Degradation of Mineral Pigments Under Soot Exposure: A Case Study of Painted Surfaces in Zhaomiao Temples, Inner Mongolia

Soot particle deposition is a common form of surface contamination in enclosed architectural environments and can significantly alter the optical appearance of painted surfaces. In the Zhaomiao temple halls of Inner Mongolia, long-term exposure to soot generated by butter lamps and incense burning has led to pronounced color darkening of mural pigments. To clarify the mechanisms by which soot deposition affects pigment optical behavior, this study investigates the surface deposition-induced color degradation of mineral pigment coatings, using Zhaomiao temple murals as a representative application context. Thirty-six typical mineral pigments were prepared as standardized coating specimens, and controlled soot deposition experiments were conducted to simulate progressive particulate accumulation on pigment surfaces. Variations in Commission Internationale de l’Éclairage (CIE) XYZ tristimulus values, luminance, and color difference (ΔE) were quantitatively analyzed under different soot-loading conditions. The results show systematic luminance attenuation and chromatic compression with increasing soot deposition, indicating that optical degradation is primarily governed by surface absorption and scattering effects introduced by carbonaceous particles. These results establish a quantitative framework based on measurable optical parameters—rather than a single absolute value—for evaluating particulate-induced optical degradation of pigment coatings. This study provides a quantitative basis for evaluating particulate-induced optical degradation of pigment coatings and supports surface condition assessment and digital reconstruction of soot-contaminated painted surfaces in architectural contexts such as the Zhaomiao temples.