The examinations were performed on the oak wood brought out in the oldest and most valuable Wielkopolska excavations i.e. in The Ostrów Tumski stronghold in Poznań and The Museum of First Piast at Lednica. The analysis of archeological sources allow to date analyze wooden materials on 10-11^th century. The estimation of degradaction state of construction elements performed with the use of microscope observations and chemical investigations revealed different content of heavy metals in comparison materials and considerable degradaction of carbohydrayte system of wood from The Ostrów Tumski in Poznań. There were found changes of content functional group and molecular mass of the most durable wooden component of wood i.e. lignin.

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