An original experimental approach to study the alteration and/or contamination of archaeological ceramics originated by seawater burial

Abstract

This paper deals with the proposal of an original experimental methodological approach specifically designed for appraising any compositional alteration and/or contamination of archaeological ceramics after the protracted contact with seawater. A series of ceramic test-pieces (briquettes and cylinders) were purposely manufactured by mixing selected calcareous or non-calcareous clays with different varieties of sieved sand temper. The aim was to reasonably simulate the ceramic pastes most frequently found in the shipwrecks recovered in the coastal areas of western Mediterranean. The used raw materials were previously characterized in terms of mineralogical and chemical composition (XRPD, XRF). The obtained test-pieces were fired under oxidizing conditions at predetermined temperatures (800 and 950 degrees C) in a traditional ceramic kiln and their chemical composition was analyzed by XRF spectrometry. Briquettes were firstly fixed into customized Ertacetal (R) holders and then placed in open sea-bed environment under monitored oxidizing or reducing conditions by the Italian CNR-IAMC dockside at Granitola, north-western Sicily. At the same time, two customized glass containers for working in a confined system under continuous seawater flow were designed and realized. They were filled with bottom sediments rather different in size in order to produce either reducing or oxidizing microenvironments below the water-sediment interface. Cylinder shaped test-pieces were placed in the sediment of both the glass containers. Weekly monitoring of temperature, salinity, conductivity, pH, Eh, dissolved oxygen was carried out in both the above-described experimental settings. Comparative (before/after) XRF analyses, after 3 months of exposure to seawater, were performed on the experimental ceramic briquettes and cylinders. The obtained results provided preliminary evidences that the proposed experimental strategy is efficiently working and a number of not negligible changes concerning major and trace elements were pointed out just after such a restricted time of exposure to seawater