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.

The Dazu Thousand-handed and Thousand-eyed Avalokitesvara is regarded as the largest and most completely preserved cliff carving of its kind in China. It is a remarkable integration of rock carving, polychromy, and gold foil application, and is regarded as the largest and most completely preserved Thousand-handed Avalokitesvara cliff carving extant in China. Recent continuous monitoring has revealed evident deterioration of the gold foil surface, primarily manifested as discolouration, cracking, and loss of the foil. A plethora of studies have examined the influence of environmental physicochemical factors and material characteristics on the corrosion of gold foil, however, the influence of microorganisms has received limited attention. The present study was conducted for the purpose of systematic characterisation of the microbial communities colonizing the gold foil surface using sterile swab sampling followed by high-throughput sequencing technology of the 16S rRNA gene and the Internal Transcribed Spacer (ITS). The results showed that bacterial communities were dominated by Firmicutes, Actinobacteriota and Proteobacteria at the phylum level, with Salinisphaera and Pseudonocardia identified as the core dominant genera. Fungal communities were primarily composed of Ascomycota and Mucoromycota, exhibiting dominance of Aspergillus, Filobasidium, and Mucor. Two dominant fungal strains (Aspergillus versicolor and Mucor fragilis) were successfully identified through selective media isolation, combined with colonial morphology observation and ITS sequence analysis. Based on the existing literature on microbial metabolism, these strains are hypothesized to facilitate gold foil corrosion via synergistic physical, chemical, and bioelectrochemical mechanisms.

The rock mass of the grotto temple has been affected by cooling and heating for a long time, which would lead to the change of the mechanical properties of the rock mass and therefore endangers the grotto temple. In this paper, the Dazu Rock Carving sandstone in Chongqing was taken as the research object, and the mechanical properties of the sandstone were studied through triaxial compression tests. Temperature change process includes high temperature (60 ℃), normal temperature (25 ℃), and low temperature (0 ℃). And the experimental process involves multiple conditions such as different heating-cooling cycle times (5 and 10 times), different durations of high and low temperatures (2 h and 4 h), and different cooling methods (natural cooling and water cooling). These test conditions were designed to analyze the influence of temperature changes on the peak stress and strain, elastic modulus, internal friction angle, cohesion, and failure mode. Results indicate that: The mechanical properties of sandstone weakened after multiple heating-cooling cycles. The values of strength, elastic modulus, cohesion, and internal friction angle decreased at different degrees. The peak strain of sandstone increased after multiple heating-cooling cycles. The failure mode of sandstone under triaxial compression was mainly shear failure with a single shear plane, while the failure mode became complex after multiple heating-cooling cycles, which resulted in the conjugated shear failure of “Y” type. Confining pressure could improve the mechanical properties, which increased the strength and elastic modulus of the sandstone samples.