Research on the Formation Mechanisms of Red Stains on Outdoor Marble Cultural Relics at Beijing Confucian Temple and the Imperial College

Stone relics exposed to outdoor environments frequently experience surface deterioration, with red stains being a common and persistent issue. The stains often observed on marble and limestone surfaces arise from complex interactions involving chemical reaction, pollutant deposition, and microbiological process. Although microbial colonization has been associated with biodeterioration, the specific mechanisms remain poorly understood. This study focuses on the red stains found on the Danbi marble carvings at Beijing Confucian Temple and the Imperial College. Combining microbial cultivation, molecular identification (ITS sequencing), SEM-EDS (Scanning Electron Microscopy), Raman spectroscopy, and HPLC-MS (high-performance liquid chromatography with mass spectrometry), we identified the pigment-producing fungus Lizonia empirigonia as the dominant agent, with no evidence of inorganic contributors such as iron/lead oxides. Metabolite profiling revealed flavonoids and polyketides as key coloring material, while controlled infection experiments demonstrated the fungus’s reliance on exogenous organic matter rather than direct stone degradation. Our findings highlight microbial activity as a primary driver of red stains in marble relics and underscore the importance of organic contaminant control in conservation.