This research develops a methodological approach to the study of ceramic glaze microstructures based on thin-section petrographic methods. Starting from its present role as an accessory identification technique, thin-section petrography turns into a pivotal tool to characterize micro-crystals embedded in ceramic glazes and hence characterise the glazes themselves. At first, the crystallites are located and described using thin-section petrographic methods. Special attention is paid on the description of the morphologies and the optical features of the crystallites. Then, the thin section petrography data are linked to compositional and structural data obtained from other analytical tools, such as SEM (scanning electron microscopy), EPMA (electron probe micro-analyser), µ-Raman (micro-Raman) and SR-μXRD (synchrotron-radiation X-ray micro-diffraction). For each mineral phase identified, chemical, mineralogical and structural data are recollected in such a way to obtain exhaustive information. This correlation allows a quick and easy identification of the crystallites in the thin section avoiding the repetition of identification protocols involving the use of expensive characterization techniques.

The presence of crystalline phases inside ancient glazes may be related to different origins: unreacted compounds, crystallites developed during glaze production or devitrification crystals formed during burial by weathering processes. This study deals with the identification of the crystalline phases developed during firing lead glazes found in medieval and modern ceramics glazes (13^th -19^th centuries). The formation of the crystallites during firing and their distribution depends on the original composition of the glaze and body (clay, stonepastes, etc.), the use of raw or pre-fired materials and on the firing conditions (temperature and atmosphere of the furnace, single or double firing, etc.). Therefore, the detailed investigation of the crystal inclusions and the microstructural heterogeneities in the glazes yields information on the nature of the objects, on the raw materials used as well as on their thermal history and several other important aspects of the glass making technology.

Roberta Di Febo will present her PhD on 21th October 2019 at UVIC-UCC, Sala Segimons Serrallonga at 11h. Tribunal Members:  Dr. Elisabetta Gliozzo, Dr. Mainardo Gaudenzi and Dr. Lluís Casas.