Electrochemical Characterization of Archaeological Tin‐Opacified Lead‐Alkali Glazes and Their Corrosion Processes

The electrochemical response of weathered and unweathered archaeological tin‐opacified glazes attached to paraffin‐impregnated graphite electrodes is described. Upon comparison with the square wave voltammetric response of SnO2, PbO and PbO2, Sn‐ and Pb‐centered reduction processes can be characterized. Reduction of Sn(IV) involves the stepwise formation of solid Sn(II) and Sn metal, successively, at potentials of −0.08 and −0.55 V vs. AgCl/Ag. Reduction of network‐modifier Pb(II) in glazes occurs at −0.5 V and is accompanied by the reduction of network‐forming Pb(IV) at potentials ranging from +0.65 to +0.20 V, confirming the presence of such centers in glazes. Voltammetric data suggest the presence of small amounts of Sn(II) resulting from the reduction of cassiterite during the firing process. A series of correlations between the peak currents can be established, indicating that the weathering process obeys a kinetic process rather than a equilibrium‐like situation.