Study On Salting Damage Analysis And Treatment Of Wall Paintings At Mogao Grottoes, Dunhuang

This paper based on the investigation and environment monitoring of salt damage of wall paintings at Mogao Grotttoes,provides an analyzing system about the dissolved salts contained in the plaster,systematically analyzing the form and distribution of the dissolved salts contained especially in the wall paintings suffered the deterioration of disruption and crater eruption,to research and develop the resin materials of super absorbing water and salt,also combining the conservation technique,to treat the salt damage wall paintings of Mogao Grottoes.The result is as the expected.Main contents as followed:?1?The salt damage wall paintings are serious and distributed widely,180 caves have this problem,the area is 836m2,most of them are located at bottom caves,the place near the edging consolidation which in early time when the wall paintings need to be rescued.According to the characters of the crater eruptions,every kind of crater eruption has been classify and named.The distribution law of crater eruption is consistent with the roads of water.?2?The yearly changing rules of temperature and humidity of caves in different types and locations are different.The caves are always in dry environment,if the high humidity appeared in short-term and change a lot,the salt damage on wall paintings will occur and develop.If the caves at the lower location and the size is large,the temperature will lower and the humidity will high,but it is not affected by outside environment easily.For the opening caves and bigger caves,the relative humidity will change a lot in one day.If the caves are big enough and at high enough locations,the temperature will change a little in one day in spring and summer,but will change a lot in winter and autumn.And the changing of temperature and humidity in one day is related with the rain closely.The micro-environment of the cave influenced by the cave is opened or not,whatever,absolute temperature and humidity,or relative temperature and humidity,they are all change a lot comparing the opened caves with not opened caves.?3?To provide the quick detecting method system aims to wall paintings suffered salt damage,combining with several methods,can satisfy different requirements,it is reliable and appropriate for determining the salt damage and to treatment them.?4?Take cave 98 as an example to study the salt containing and distribution in different locations and depths on the disruption.Found that,the salt contents of the western wall is highest,average is closed to 2.5%,the eastern wall is lowest,average is less 0.8%,the salt contents distribution of dissolved salt in every wall gradually increased from eastern wall to western wall.The salt contents gradually reduced followed the depth increased,on the surface of the wall is 6.5%,it is the double of the bottom layer.The dissolved salts of the plaster mainly are Na⁺,Cl^-and SO₄^2-,occupied 91% of the total components.?5?Using several methods to analyze the crater eruption and plaster of the wall paintings which suffered the crater eruption,the results obtained from every method could be mutual verified and supported.Using SEM can observe the Na Cl crystals clearly,which are cubic or cube-like salt crystals.Using SEM-EDS can scan the surface and profile of the crater eruption,and the characters of the distribution of Na and Cl also can be observed.Most of the salt contents of the crater eruption particles are 20%-30%,mainly are Na⁺,Cl^-.Analyzed by SEM-EDS,found that Na,Cl,S,Ca,K are the main elements formed the crater eruption.From the image catched by HRTEM and also EDS has been used,found that the crater eruption contains most of Na Cl and a little of other soluble salts/slight soluble salts,which about more than ten kinds.Analyzed by XPS and showed that,Na exists as the form of Na Cl or Na2SO4;S exists as the common form of sulfate.Analyzed by XRD and showed that the soluble salts contained in crater eruption are mainly NaCl.Determining and verified by several analyzing methods,found that NaCl is the main ingredient of the crater eruption,and also contains other salts,such as: Na₂SO₄,CaCl₂,Na NO₃ and CaSO₄.The soluble salts contained in the plaster of suffering crater eruption deterioration is 5%,in normal area is less 2%.Different from disruption wall paintings,the distribution of the salts in different layer of the plaster of crater eruption wall paintings is average,the main salts are Na⁺ and Cl^-,Ca²⁺ and SO₄^2-are minority.The crater eruption is formed by the water contained NaCl and entering into the plaster.?6?The test of simulated deterioration wall paintings has been done,found that different salts,salt contents and outside environment can cause salt damage with different types and in different degrees,the simulation test verified the situation observed in-situ,and also provide the reference data for wall paintings restoration.?7?To carry on the study of treatment technique of salt damage wall paintings and causing mechanism.Applying the resin materials of super absorbing water and salts,using the vacuum desalt board and to do twice desalt,so can reduce 40% salt contents in the detachment plaster which have been grouting,and more than 95% salt contents can be reduced on the surface layer.In such a way,to treat the disruption wall paintings,more than 50% salt contents in the plaster can be reduced,and more than 90% salt contents can be reduced on the surface layer.If the salt damage wall paintings have been treated,the soluble salt contents in wall paintings could be in a safe level,and the strengthen of wall paintings has been increased,the picture quality of wall paintings appears better.Through 2 years observation and monitoring,the situation of the salt damage wall paintings which have been treated is stable.