From the burial environment to the laboratory: the analytical challenge of archaeological wood

This PhD thesis aims at studying structural and chemical changes undergone by archaeological wood during ageing in different environments, in presence of inorganic components and consolidating agents. Archaeological wood samples, artefacts and shipwrecks of different geographical origin were investigated, mainly using pyrolytic techniques coupled with gas chromatography and mass spectrometry (Py-GC/MS, EGA-MS). The results were integrated with those obtained by other techniques, i.e. scanning electron microscopy – Energy dispersive X rays spectroscopy (SEM-EDX), Fourier transformed infrared spectroscopy (FTIR), synchrotron radiation based micro-FTIR, classical wet chemical methods, X-rays diffractometry (XRD), inductively coupled plasma - optical emission spectroscopy (ICP-OES), ionic chromatography (IC). The new achievements provided by this PhD thesis were obtained by following the steps below: - optimisation of a Py(HMDS)-GC/MS method for the analysis of consolidated/unconsolidated archaeological wood, using an EGA/PY-3030D Pyrolyser (Frontier Lab); - construction of a library for the recognition and semi-quantification of the silylated derivatives of wood pyrolysis products, using the AMDIS software (Automated Mass spectral Deconvolution and Identification System); - identification of relevant analytical parameters to assess wood degradation on the basis of the obtained pyrolysis profiles; - development of a new procedure based on EGA-MS applied to archaeological wood; - application of complementary techniques (SEM-EDX, FT-IR, synchrotron radiation based micro-FTIR, classical wet chemical methods, XRD, ICP-OES, IC) for the analysis of archaeological composite wooden artefacts; - integration of the results obtained by multi-analytical approaches for relevant case studies. Particular attention was paid to the strategy of interpretation of analytical data and new potentialities of Py(HMDS)-GC/MS are here reported. In particular, the categorisation of holocellulose and lignin single pyrolysis products was proven to be necessary, in order to obtain information about the preservation state of the single wood components, and overcome some limitations related to the simple calculation of the holocellulose/lignin ratio as a degradation index. In addition, the interpretation and discussion of the data obtained by EGA-MS for the analysis of archaeological wood is presented here for the first time. Finally, relevant correlations between the results on the organic and inorganic content in archaeological wood obtained by different techniques were successfully established, proving the validity of the adopted multi-analytical strategies.