Investigation of Archaeological European White Elm (Ulmus laevis) for Identifying and Characterizing the Kind of Biological Degradation

Abstract

The current work aims at the study of the biological degradation of archaeological European white elm via microscopy and chemical analysis in order to identify the kind of biological degradation and characterize the state of preservation of this type of wood. Profound knowledge of the chemical constituents and biological degradation in fresh-cut and archaeological elm wood will simplify the process of restoration and conservation of the investigated artifacts. Therefore, fresh-cut and archaeological elm were compared in terms of extractive, chlorite holocellulose, α-cellulose, lignin, and ash contents. In the fresh-cut elm wood, the contents of Kürschner–Hoffer cellulose, chlorite holocellulose, α-cellulose, and hemicellulose were significantly higher than that of the archaeological elm, confirmed by the degradation of native wood hemicelluloses by erosion bacteria during soil contact. Naturally, the mass percentage of lignin increases as the amount of chlorite holocellulose in the wood decreases. These wet chemistry results were also confirmed by FTIR analysis, where bands mainly attributed to hemicellulose and cellulose decreased significantly and bands belonging to lignin display higher intensity for the archaeological specimens. Ash and cyclohexane–ethanol extract contents of archaeological elm wood were significantly higher due to the movement of mineral components arising out of the soil into the wood specimens. Based on the microscopic investigation and given the fact that wood decay fungi need oxygen to degrade wood and the investigated archaeological elm specimens were buried to a 10 m depth in the soil, we might conclude that the wood degradation was caused by erosion bacteria.