Degradation Mechanisms of Traditional Pigments Used in Historic Artworks Within National Heritage Temple Halls

The pigment materials are inevitably subject to degradation, which reduces the readability of artwork and impedes the understanding of its intrinsic cultural heritage value. This work presents a scientific investigation of the degradation mechanism of dancheong, a type of traditional Korean artwork typically painted on wood blocks, using the Gakhwangjeon, a national heritage temple hall of Hwaeomsa, as a case study. The physicochemical analyses reveal that traditional pigments experience color fading resulting from light-induced oxidation, leading to a loss of color brightness, contrast, and original chromaticity. Both on-site and lab-based analyses demonstrated that the high valence of Fe⁴⁺ or Pb⁴⁺ observed in the deteriorated artworks is attributed to the light-induced oxidation of Noerok (celadonite) and Seokganju (hematite) or the oxidation of Yeonbaek (lead white), respectively, using X-ray fluorescence and X-ray photoelectron spectroscopy. Colorimetry analysis further demonstrates that while the oxidation of Fe and Pb, causing the degradation of Noerok and Seokganju used as the green and red pigments, respectively, alters the chromatic difference in the artworks, the oxidation of Pb in Yeonbaek, used as the white pigment, results in decreased lightness, along with chromatic changes, due to its transformation into a lead red-like structure. Moreover, the chromatic difference is significantly smaller than the lightness difference, indicating that color fading is primarily attributable to the oxidation of Pb rather than Fe.