The Condition Survey Of Wall Painting Of Cave 196 In Mogao Grottoes

Dunhuang served as an important oasis,trading town and administrative center on the Silk Road in ancient.Both vivid sculptures and beautiful wall paintings in Mogao Grottoes have represented the wisdom and talent of the ancients.But now large scales of paintings have being deteriorated by flaking,powdering,efflorescence and other diseases due to the impacts from environment and human being.As we all know disruption and blister have been the most serious disasters for wall paintings in Mogao Grottoes.Most of them exist in Cave 196 excavated in Tang dynasty.So wall paintings of Cave 196 must be restored immediately.According to the Principles for the Conservation of Cultural Heritage in China,When you want to restore the cultural relics,The initial step should be effective condition survey and research.In this work the study mainly includes value assessment,environment monitoring,diseases survey and so on.Portable microscopy,portable X-ray fluorescence spectroscopy,X-ray powder diffraction,laser particle size analyzer and micro-Raman spectroscopy have been applied to obtain the information on pigments and renders.Besides the effects of the external atmosphere including temperature,relative humidity,and rainfall on the microenvironment of different locations and height is also studied in Cave 196.Finally species and contents of soluble salt causing disruption and blister are analyzed.These results play an important role in desalination and restoration of wall paintings in Cave 196 in the future.The monitoring results indicate atmosphere environment affect temperature and relative humidity in Cave 196.The temperature shows a trend of decreasing first and then decreasing and the highest temperatures appeare in July.However Relative humidity changes more complex than temperature.Temperature and relative humidity change obviously when the detector is close to the outer environment.When it rains,relative humidity is over 65%.It may be active soluble salts in cave.Besides the influences of atmosphere environment on temperature and relative humidity of the different height of Cave 196 is also studied.Finally we also find the door is useful for stop the air from entering the caves.The analysis results of materials and techniques of wall paintings in Cave 196 indicate the structure of painting include support,coarse plaster,fine plaster,grounding(80-110um),pigment layer(10-26um)from inner to outer.Support is composed of conglomerate which hasn't extreme resistance to water resistance.Wheat straw and hemp are added to the renders to increase the performance of render.The contents of each organic fibers are about 10% more than other caves.The raw material of renders is Dengban soil composed of quartz and albite gotten from Daquan River.Grounding is mixture of calcite and talc.The pigments used for wall painting are mostly inorganic mineral pigments.They consist of hematite,red lead,cinnabar,azurite,atacamite,orpiment and so on.Besides the mixture of langite and atacamite was used to form the blue-green colour.The result of disease survey indicates the painting diseases mainly include fading,colour changing and paint loss in antechamber.Whose area accounts for 80% of total wall area in antechamber and the salt damage of wall paintings is selective and destructive in the main chamber.So the soluble salts in Cave 196 are analyzed by ion chromatography.The analytical results indicate the salt content of west wall is up to 3% where the content of soluble salts is the highest area.Soluble salt ions are mainly chloride ions sodium ions and a small amount of sulfate ions.So It can be concluded that soluble salts are sodium chloride and sodium sulfate.Besides the soluble salts of disruption area in the south wall of antechamber and blister area in the main chamber are single sodium chloride.However soluble salt is mainly sodium sulfate in north wall of antechamber.The loose render is caused by the joint action of soluble salt and biological destruction.So due to environmental monitoring results and soluble salt,Humidity control will be effective in preventing salt damage for conservation in Cave 196.