Electrochemical analysis of coffin portraits from the National Museum in Krakow

An electrochemical study was conducted on a series of samples taken from the metal supports of ten coffin portraits and one funeral portrait from the collection of the National Museum in Krakow (Poland) as a part of a research project aimed to their study and preservation. An approach that makes use of voltammetry of immobilized particles (VIMP) methodology was necessary due to the need of minimizing the amount sample taken from each object and the presence of areas with different corrosion patterns denoted by different color and texture. An initial XRF spectrometry survey of the metal supports was performed to determine the main elements present and develop a sampling strategy for studying their corrosion products. The studied portraits contain supports made of Cu as well as Sn–Pb, Ag–Cu, and Cu–Zn binary alloys. Solid-state voltammetric techniques also allowed to identify and discern between different corrosion products present in the objects. Voltammetric data for copper- and lead-based supports were also fitted to available calibration graphs for dating purposes. The resulting dates remain within an acceptable error range when compared to those provided by the historians.