Effects of sealing materials on the physiological metabolism and corrosion action of Mucor fragilis on the gold foil surface of the Thousand-handed and Thousand-eyed Avalokitesvara

The Dazu Thousand-handed and Thousand-eyed Avalokitesvara is widely regarded as a seminal example of Song Dynasty grotto art. Although the statue was restored in 2015, the preservation environment has not been effectively improved. It still suffers from issues such as gold foil delamination, cracking, and microbial erosion. Preliminary investigations by our research group into the microbial corrosion mechanisms on the gold foil indicated that the substrates generated from microbial metabolism could induce microbial colonization and alter the microenvironment of the gold foil surface. Nonetheless, the relationship between sealing materials and the microbiological colonization and corrosion processes on gold foil remains insufficiently studied. The present study established a Mucor fragilis-based culture system, incorporating raw lacquer, turpentine-modified lacquer, and tung oil-modified lacquer as sealing materials. These systems were combined with simulated corrosion experiments on gold foil surfaces to systematically evaluate the effects of different sealing materials on microbial physiological metabolism and the corrosion process. The results indicated that raw lacquer formed a stable biofilm structure with Mucor fragilis, providing both physical barrier and inhibition of organic acid secretion, thereby offering effective protection for the gold foil. Although the film morphology of turpentine-modified lacquer was relatively heterogeneous, its sustained mildly alkaline environment and low extracellular polymeric substances (EPS) concentration effectively suppressed microbial adhesion, suggesting a certain long-term protection potential. Tung oil-modified lacquer initially inhibited microbial growth through oxidative stress, but its protective effect diminished over time as fatty acid components were utilized as carbon sources.