Pigment Identification And Related Microbial Research At Dazu Rock Carvings

The Mount Baoding Carvings is the largest and most exquisite part of the World Heritage Dazu Rock Carvings.The Niche of Sakyamuni Eentering Nirvana(Sleeping Buddha)is not only the largest of the Dazu Rock Carvings,but also the world’s largest Buddha statue featuring only the upper part of the body,with great historical,artistic and scientific value.However,the Dazu Rock Carvings are located in the high temperature and humidity of Chongqing,and the suitable temperature and humidity conditions have caused many moldy spots to grow on the surface of the painted layer,and it was found that the moldy degree of different pigments varied,with the most serious mold on the surface of blue pigment,and even some areas completely turned black.In view of this phenomenon,this paper analyzes the composition of different colors of pigments to reveal the relationship between the degree of mold and the type of pigment.On the basis of the microbial identification of the painted layer,the identified strains were inoculated on the simulated painted samples to verify the differences in the degree of mold on the surface of different pigments to explore the mechanism of mold damage.The main research contents include.(1)Scientific and technical analysis of the composition of painted pigments.Scanning electron microscope spectroscopy and Raman spectroscopy were used to analyze the pigment composition of the painted layer of the Dazu Rock Carving.The results show that the white base material is gypsum of high purity,The red,blue,green,white and black pigments decorated the surface was identified to be red ochre,synthetic ultramarine blue,lavendulan,cerussite lead white and mimetesite mixture,carbon black;the gold foil attached to the surface is gold mixed with a small amount of silver.Among these pigments,red ochre,ultramarine,carbon black,and lead white are common pigments;while lavendulan and mimetesite are rarely used as pigments,especially mimetesite is found for the first time in the white pigment layer of Dazu Rock Carvings.It is presumed that lavendulan may be the degradation product of emerald green,and mimetesite may be the secondary product of emerald green and lead white.(2)Identification of microorganisms in the painted surface layer.Using the traditional isolation and culture method to isolate and purify the Dazu microbial samples to obtain three pure culture strains,and then using traditional biological methods to observe the morphology and microstructure of the colonies were initially judged to be fungi,two of which were molds and one was yeast.On this basis,β-tubulin sequence determination was used to accurately identify two species of mycobacteria as Parengyodontium album and Cladosporium halotolerans,while the yeast did not compare the results.Combined with the literature,it can be seen that the identification of the two species of mold have salt tolerance,moisture-loving characteristics.Dazu Sleeping Buddha statue in the environment of high temperature and humidity,the rock contains a lot of salt,this special environment is in line with the above-mentioned environmental characteristics of mold growth,two strains of fungi were isolated from the surface of the Sleeping Buddha also reflects the Sleeping Buddha water disease and salt disease is more serious.(3)The mold variability and damage mechanism of the study.The identified strains of Cladosporium halotolerans were inoculated onto the medium and painted samples containing nine common pigments of ancient China: ultramarine,red ochre,cinnabar,azurite,malachite lead red,lead white,realgar,and orpiment,to evaluate the growth,observe and explore the differences in their growth;while using Fourier infrared spectrometer,X-ray diffractometer,spectrophotometer The effects of the growth of the strains on the colored glue,pigment composition and appearance were studied by Fourier infrared spectroscopy,X-ray diffractometer,spectrophotometer and scanning electron microscope to reveal the damage mechanism of the colored paintings.The experimental results showed that the microbial growth on different pigments was ranked as follows: ultramarine > cinnabar > red ochre >lead white > malachite ≈ azurite > orpiment > realgar > lead red,which is consistent with the phenomenon observed in the Dazu Sleeping Buddha,verifying the variability of microbial growth on different color surfaces,and the main factor for this variability is the chemical composition of the pigments.Mold damage to the color painting is mainly on the role of the adhesive material,the experimental period in this experiment was not found to have an impact on the pigment composition,but will cause significant changes in the color of the painting,the main reason is that the mold itself has color,the growth of colonies attached will change the color of the original painted pigment,the more vigorous its growth,the greater the change in surface color.At the same time the growth of mycorrhizal nutrient mycelium will cause mechanical damage,presumably in the Dazu Sleeping Buddha environment,microbial disease can cause more serious damage in concert with salt damage,water damage.This paper reveals the reasons for the variability of mold on the surface of the Dazu Sleeping Buddha and the mechanism of mold damage,as well as what kind of pigments used in the painted relics are more vulnerable to microbial disease threats and more urgent to prevent and control.For the realization of the " raw materials and original technology " to provide a scientific basis for the protection and repair of painted relics microbial disease prevention and control to provide a scientific basis.