Effect of firing temperature and atmosphere on ceramics made of NW Peloponnese clay sediments. Part I: Reaction paths, crystalline phases, microstructure and colour

Archaeometric investigation on ancient ceramic collected from excavations in NW Peloponnese demonstrated that the ancient potters used the local Plio-Pleistocene clay sedimentary deposits for a large historical period. Three representative raw materials of these local sediments were chosen for experimental work aiming to evaluate their firing behaviour in a propane-fired kiln, with a different atmosphere and temperature. The determination of mineralogy and microstructure was carried out by XRD and SEM-EDS analysis. For ceramics fired at 850 and 950 degrees C, no significant mineralogical and microstructural differences were observed between the oxidising and reducing atmosphere. The main pyrometamorphic phases are fassaite, gehlenite, anorthite and wollastonite. On the contrary, at 1050 degrees C in reducing atmosphere, gehlenite and wollastonite are diminished whereas the content of anorthite, fassaite and amorphous phase is higher. The higher vitrification is attributed to Fe2+ that participates either in the formation of eutectic phases or in low melting crystalline phases. (C) 2010 Elsevier Ltd. All rights reserved.