Firing techniques of the impasti from the protohistoric site of Concordia Sagittaria (Venice)

Relevant information on the technology employed in the production of concotto and coarse pottery was derived mainly by 57Fe Mossbauer spectroscopy. The concotto and the coarse pottery are two types of fired clay mixtures unearthed from the protohistoric settlement site of Concordia Sagittaria. The concotto pottery was produced by firing clay mixtures under oxidizing conditions at high temperatures in kilns, or at lower temperatures in open air. The firing of these clay mixtures, containing partially ground pieces of waste pottery, resulted in hard, impermeable and coloured construction materials, particularly suitable for humid environments. In turn, the coarse pottery was produced by firing clay mixtures less heterogeneous than those of the concotto. The firing was performed under reducing conditions at high temperature with a final exposition to air by opening the still hot kiln. This firing technique yielded light and agreeable coarse pottery with a red-coloured surface covering the grey-black core. Both the ancient firing techniques were substantially reconstructed by comparing the Mossbauer patterns of the artefacts with those of the replica samples produced from local clay fired in the laboratory.