Cleaning Old Icons: The Effect of Varnishes on the XRF Analysis of Portable Panel Paintings

Portable icons, i.e. religious paintings on wooden supports/panels, have been continuously produced in the area of Greece from the first Christian centuries to the present time. The icons are covered by one or more layers of varnish which is originally applied in order to protect the underlying painting from various deterioration factors (such as wear) and to improve the appearance of the artifact. However, in the course of time varnishes gradually decay through processes that impart color and other changes. Therefore, the removal of decayed varnishes—an intervention called “cleaning” in the context of artworks conservation—is often required. In this work we examine whether the old varnish layers affect the results of X-ray fluorescence (XRF) analysis, an analytical technique that is widely used for the identification of pigments and other painting materials. For this purpose, selected areas of various post-Byzantine icons are analyzed by portable XRF before and after cleaning interventions and the relevant XRF spectra are subject to comparison. For the purpose of better understanding the varnish effect, old (i.e. eighteenth-nineteenth century) varnish recipes are also considered. The results demonstrate that the varnishes may affect significantly the obtained XRF spectra and, hence, certain conclusions as regards painting materials.