Aging and Discoloration of Red Lead (Pb3O4) Caused by Reactive Oxygen Species Under Alkaline Conditions

Abstract

Red lead (Pb3O4) has been extensively utilized as a red pigment for centuries. However, the discoloration and blackening of red lead in historical paintings have significantly compromised the aesthetic value of mural artworks. Investigating the mechanisms behind the blackening of Pb3O4 is of paramount importance. This study examined the effects of four kinds of reactive oxygen species (ROS) on the aging process of Pb3O4 in an alkaline environment. Specifically, singlet oxygen (1O2), superoxide radical (O2−·), hydrogen peroxide (H2O2), or peroxynitrite (ONOO−) was individually reacted with Pb3O4. The resulting products were analyzed qualitatively and quantitatively using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), and UV-Vis spectroscopy. The findings indicate that singlet oxygen (1O2) and superoxide radicals (O2−·) effectively induce the aging of Pb3O4, whereas hydrogen peroxide (H2O2) and peroxynitrite (ONOO−) exhibit little impact on its aging. This research elucidates the aging mechanisms of Pb3O4 in alkaline environments and provides valuable insights for the preservation and restoration of mural paintings.