Testing Pleco to investigate the tarnishing of gilt silver threads, sequins and foils adorning the coronation mantle of Charles X

June 21-22, 2023

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The coronation mantle of Charles X (King of France between 1824 and 1830) is the only surviving coronation mantle of a French king. It is made of velvet and rich embroidery constituted of gilt silver threads, sequins, and foils. Preserved in the Palais du Tau, Reims, France, for almost two centuries, it has become tarnished over time. Because of their complex surface and their fragility, it was impossible to clean all metal decorations with conventional techniques like mechanical cleaning. The conservation team (composed of three textile specialists Carine Istria, Gael Hennion and Antoinette Villa as well as two metal specialists Julie Schröter and Géraldine Aubert) commissioned to clean the mantle therefore wanted to test Pleco both as an analytical tool to determine the nature of the black tarnish and as a cleaning tool. Linear scanning voltammetry plots obtained with the OGF01A potentiostat kindly lent by Origalys showed the presence of thick and compact silver sulphide (Ag2S). The cleaning will be carried out in two steps: first the reduction of Ag2S to Ag and then the dissolution of the reduced Ag to Ag+ to recover the golden aspect.