Microstratigraphic and mineralogical study of a Late Bronze Age updraft pottery kiln, Kolonna site, Aegina Island, Greece

Ceramic kilns are an indispensable part of the study of ceramic technology. Studies on the construction and maintenance of ancient ceramic kilns are mostly based on field observations during excavation. Here we report on the micromorphological study of a Late Helladic updraft ceramic kiln from the archeological site of Kolonna, Aegina Island, Greece. The study is focused on the construction details and stratigraphy of the interior of the kiln and also on the ashy sediments of the entrance area with the aim to better understand the operation of the kiln. In addition, X-ray power diffraction (XRPD), Fourier transform infrared (FTIR) spectroscopy, and FTIR microspectroscopy, applied directly on thin sections, provided information on the temperature of firing and on the observed mineralogical transformations. A highly calcareous clay was used for the construction of the kiln. The main construction of the kiln was followed by two major reconstructions affecting both the walls and floor, but not the door area. In between the reconstruction phases, the kiln was left open for considerable periods, probably during the rainy seasons as attested by the preservation of water-lain sedimentary crusts on the floor of the kiln. The firing process formed a poreless, well-reacted sealing crust on the inner surfaces of the kiln which presumably acted as an insulating shell. Calcitic ashes have been transformed to quicklime and hard indurated surfaces resembling lime constructions. The mineralogical transformations suggest firing temperatures in excess of 700 degrees C but probably lower than 900 degrees C. The use of highly calcareous material for the construction of the kiln, generally considered not suitable for its inferior thermal insulating properties and strength, is discussed in the light of the observed mineralogical transformations and fabric.