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

This paper deals with the proposal of an original experimental methodological approachspecifically designed for appraising any compositional alteration and/or contamination ofarchaeological ceramics after the protracted contact with seawater. A series of ceramic testpieces(briquettes and cylinders) were purposely manufactured by mixing selected calcareousor non-calcareous clays with different varieties of sieved sand temper. The aim was toreasonably simulate the ceramic pastes most frequently found in the shipwrecks recovered inthe coastal areas of western Mediterranean. The used raw materials were previouslycharacterized in terms of mineralogical and chemical composition (XRPD, XRF). Theobtained test-pieces were fired under oxidizing conditions at predetermined temperatures (800and 950 °C) in a traditional ceramic kiln and their chemical composition was analyzed byXRF spectrometry. Briquettes were firstly fixed into customized Ertacetal® holders and thenplaced in open sea-bed environment under monitored oxidizing or reducing conditions by theItalian CNR-IAMC dockside at Granitola, north-western Sicily. At the same time, twocustomized 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 sizein order to produce either reducing or oxidizing microenvironments below the water-sedimentinterface. Cylinder shaped test-pieces were placed in the sediment of both the glass containers.Weekly monitoring of temperature, salinity, conductivity, pH, Eh, dissolved oxygen wascarried out in both the above-described experimental settings. Comparative (before/after) XRFanalyses, after 3 months of exposure to seawater, were performed on the experimental ceramicbriquettes and cylinders. The obtained results provided preliminary evidences that theproposed experimental strategy is efficiently working and a number of not negligible changesconcerning major and trace elements were pointed out just after such a restricted time ofexposure to seawater.