D-pepAg - Determination of electrolyte parameters for the cleaning of silver (Ag) artefacts

September 2024

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The doctoral research project D-pepAg (Determinazione dei parametri elettrolitici per la pulitura di manufatti in argento (Ag)) of Nicola Ricotta at the SAGAS Department of the University of Florence was carried out at the Opificio delle Pietre Dure on collections from the Tesoro dei Granduchi in Palazzo Pitti, Gallerie degli Uffizi, Florence.

The main objective was to use Pleco, developed at Haute Ecole Arc Conservation-restauration in Neuchâtel, Switzerland and distributed as an open-source kit for self-assembly with parts manufactured using innovative, low-cost technologies, both as an analytical tool for identifying tarnish and determining cleaning parameters as well as a local electrolytic cleaning tool.

The stability of the glassy carbon used as a reference electrode was studied, and the sealing of the electrolytic cell was improved for total control of Pleco. This allowed the development of a protocol for using the tool, ensuring representative, reproducible, and accurate data. The results, obtained from artificially aged silver-based alloy coupons, were then applied to the investigation and cleaning of two key objects from the collections of the Tesoro dei Granduchi: a bas-relief depicting the Last Supper, made in the late 16th and early 17th centuries by Matthias Walbaum, and a cooler made in 1810 by Giuseppe Valadier.

It was possible to highlight and propose solutions for two of the most relevant issues in silver conservation: surface heterogeneity and level of cleaning. Using the Pleco, it was possible to determine the nature and distribution of the tarnish, define electrolytic cleaning parameters, reduce tarnish while minimizing material loss, and recover the gilding that had been altered by silver tarnish.