A Comparative Study On Consolidation And Dehydration Of Waterlogged Archaeological Woods

Waterlogged archaeological woods are highly hydrated wooden relics discovered during the excavations.It has a wide range of coverage,including large wooden structures such as inner and outer coffins,wooden furniture,architectural structures,shipwrecks,bridge foundations,and other small burial articles including wooden-cored lacquerwares,wooden figurines,comb etc.They are commonly found in archaeological excavations and hard to be preserved.The high soil moisture content of southern part of China makes wooden relics highly waterlogged.The internal fiber structure is damaged by bacteria decay,even when the appearance seems complete by the time it was excavated.Once exposed to air,it will quickly decay in a few minutes.The conservation of waterlogged archaeological woods has always been the focus of scholars at home and abroad.Scholars have studied many different aspects,including the environment of conservation,on-site excavation,microscopic observation,mechanism of degradation,methods of consolidation and dehydration and so on.The status of conservation of waterlogged archaeological woods mostly depends on the environment it is surrounded by.The microorganism decay of waterlogged archaeological woods is directly influenced by the composition of sediment,groundwater level,the seasonal change of groundwater,pH,eH and the dissolution of oxygen.The monitoring of the environment is very important during the excavation.Ordinary reburial after excavation cannot reach the most suitable environment for conservation.There for it is the best plan to carry out dehydration right after excavation if the original environment is disturbed.The fiber structure of waterlogged archaeological woods can be clearly observed using microscope.The types of bacteria and the effect of decay can be identified by the morphology of wood cells.Microscope can also be used to search for soluble salt crystals,especially sulfate and iron sulfides.The mechanism of degradation of waterlogged archaeological woods can be understood by analyzing the content of cellulose,hemicelluloses and lignin using X ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FT-IR),Gas Chromatography-Mass Spectrometer(GC-MS),Nuclear Magnetic Resonance(NMR),etc.Cellulose loss makes its color turning darker when expose to light and oxygenated.The loss of lignin makes it easily damaged by exogenous process.The gain and loss of water in waterlogged archaeological woods are determined by the chemical potential of the water in the wood relics and which in the environment.The drier the environment or higher the temperature is,the greater the potential energy,the faster the loss of water,and the greater the shrinkage and deformation will be.After soaking in conservation agents,such as Polyethylene glycol(PEG),the shrinkage of wood can reduce slightly.It is found that there is few discussion about optimization experiment on dehydration of waterlogged archaeological woods based on the summary of literatures,especially on the combination of the new consolidation materials and the PEG.Accordingly,the waterlogged coffin found in Chutai site in Fuyang,Anhui Province in the late stage of the Warring States period and wooden desk found in Wanfang Square metro station Nanjing,Jiangsu Province in Han Dynasty were studied.In the experiment,photograph was taken to observe the samples.Tree species were identified,size were measured,moisture content and color change were calculated.PEG400,PEG800,PEG3000,hydroxypropyl cellulose,trehalose,sorbitol,mannitol and other conservation agents are accompanied by vacuum freeze-drying used to consolidation and dehydrate of the samples.The experimental results show that the best result can be achieved through the combined action of PEG3000 and trehalose.Through repeated experiments,the operation of vacuum freeze-drying is optimized,so that the deformation of waterlogged archaeological woods can be minimized.