Unveiling the original layers and color palette of 18th century overpainted Transylvanian icons by combined X-ray radiography, hyperspectral imaging, and spectroscopic spot analysis

This paper presents the results of an in-depth diagnostic investigation carried out on four Transylvanian icons originally painted at the beginning of the 18th century and entirely repainted later, in 1911. The icons, originating from a wooden church in Alba County (Romania), were investigated by an array of non-invasive and micro-invasive techniques that included: multi- and hyperspectral imaging, digital radiography, X-ray fluorescence, and Fourier transform infrared spectroscopy. Combined imaging techniques allowed extraction of information from the original pictorial layer and highlighted the original inscriptions. Spectroscopic analysis carried on micro-samples identified many traditional pigments used in Byzantine iconography such as: lead white, red lead, orpiment, red ochre, yellow ochre, and umber. The presence of zinc white, Prussian blue, and some chromium-based pigments in the upper paint layers was directly associated with the repainting. Information on the used painting technique was also obtained, as well as a series of informative technical details that shed light on the complex history of the icons, while offering at the same time new knowledge on the materials and painting techniques used in Transylvanian workshops, between the 18th and 20th century. Overall results allowed characterization and discrimination of the original painting materials and those present in the repainting, and helped conservators with the restoration of the objects.