A diverse study on UVA aging behavior and influencing factors of safflower red, lac, and alizarin lake pigments in painted cultural relics

Photodegradation, particularly induced by ultraviolet radiation, is a major cause of discoloration in organic pigments, though studies on their UV aging behavior remain limited. This work investigated the effects of binder type, environmental humidity, temperature, and plaster composition on the UVA aging behavior of three representative red organic aluminum lake pigments (safflower red lake, lac lake, and alizarin lake) using colorimetry, ATR-FTIR spectroscopy, mass spectrometry (MS), and analysis of variance (ANOVA). The results demonstrated that binder type and concentration, humidity, temperature, and plaster layer composition all significantly influenced the discoloration rate of pigments under UVA-induced. High temperature, high humidity, and alkaline plaster layers accelerated UVA degradation of pigments, whereas linseed oil formed a protective film that mitigated degradation of pigments. MS analysis confirmed that external factors did not alter the characteristic pigment markers, which ensured reliable identification of these lake pigments in cultural relics. These findings provide theoretical support and practical guidance for the conservation and identification of organic aluminum lake pigments in cultural heritage, highlighting their considerable practical significance.