A multi-analytical approach for the validation of a jellified electrolyte: Application to the study of ancient bronze patina

This work reports the first employment of a gel polymer-based electrochemical cell to perform electrochemical impedance analysis of archaeological remains. The patinas of three Roman coins are studied through of electrochemical techniques (especially Electrochemical Impedance Spectroscopy, EIS) along with Electron Scanning Microscopy (SEM-EDS) and X-ray diffraction (XRD), in order to validate the results obtained with jellified electrolyte. SEM-EDS and XRD analyses reveal the composition of the patinas suggesting that the original alloys were made of Cu and Cu-Sn-Pb. Furthermore, EIS results make one able to assess some characteristics of coins, as for instance, the presence of a noble patina. This outcome is corroborated by the SEM-EDS and XRD analysis, suggesting that the method based on the jellified electrolyte on archaeological samples can be employed. Moreover, supporting studies are carried out using Voltammetry of Microparticles (VMP), which is able to detect the presence of some specific corrosion products (cuprite). So far, EIS is not a common technique in the Cultural Heritage field despite it can provide useful information about the conditions of conservation, i.e., corrosion processes. Here we can show the advantages of developing a gel-based system for EIS measurement which allows carrying out a punctual and quick analysis on the ancient bronze roman coins.