Archaeometric studies of historical ceramic materials

Abstract

The aim of the PhD research was to define a scientific methodology able to correlate the production techniques and the chemical and physical characteristics of traditional ceramic materials. The methodological approach considered traditional techniques employed in archaeometric research, and the use of innovative methods only recently applied in CH material investigation, in order to develop an effective and innovative methodology for the study of this kind of materials. The research was performed at first by studying the relationship between raw material composition, firing temperatures and the final chemical-physical features of raw ceramic samples ad hoc made in laboratory, following traditional methods and using different kinds of raw clay materials and firing temperatures. Subsequently, through the reverse process, potteries of different provenance and age were analysed in order to verify the correlation between the production techniques and the characteristics of the ceramic materials. Archaeological potteries from Torcello, one of the first settled islands on the northern Venetian lagoon, alongside historical ceramic sherds from Central and Eastern German sites, never investigate before, were selected as interesting case studies for the research project. The ceramic samples were studied using chemical, physical and petrological techniques, with the joint use of traditional and non-traditional methods. Chemical composition, mineral phases, microstructure as well as morphology of pottery depend on the native material composition, technology and conservation state. Considering these distinctive properties, the samples were investigated by a multi-analytical approach by optical e morphological studies (Polarizing Microscopy (OM), Scanning Electron Microscopy (SEM)), chemical characterization (X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FT-IR), micro-Raman spectroscopy, X-ray Fluorescence (XRF)) and microstructural analysis by Mercury Intrusion Porosimetry (MIP). The proposed innovative approach included chemical and morphological analysis, encouraging the use of non-destructive techniques. UV-Vis spectrophotometry, Laser Induced Fluorescence (LIF) and the micro-destructive Laser Induced Breakdown Spectroscopy (LIBS) were applied to deepen the chemical characterization and the production techniques of the ceramic glaze present in the historical potteries. LIF technique was applied to study both the ceramic glaze and matrix composition of the potteries exploiting the mineral luminescence. The results were integrated and combined with those obtained by UV-Vis spectrophotometry, XRF and LIBS, which was able to provide highly sensitive qualitative elemental data. Morphological studies were carried out by X-ray micro-Computed Tomography (μ-CT), which provided a complementary microstructural investigation of the ceramics respecting the integrity of the artefact. UV-Vis spectrophotometry, LIF and μ-CT, only recently applied within conservation science but not yet widely employed within archaeology, offer the advantage of being non-destructive. Despite the fact that LIBS technique is micro-destructive (with a minimal loss of material and order of fractions of micrograms), its ability to analyse materials in laboratory or in situ conditions is highly appreciated. The obtained results encourage the application of the laser techniques in archaeological and historical ceramics. Furthermore, X-ray μ-CT permited the implementation of the data previously obtained by traditional techniques, offering the possibility to investigate the role of close porosity and its behaviour during the firing processes. Furthermore, this research has been able to collect innovative results in order to estimate the firing temperature and technology of the ceramic sherds, thus expanding the knowledge upon pottery production in Torcello and in central-Eastern Germany.