Copper resinate: an XPS study of degradation

In this paper, we describe an X-ray photoelectron spectroscopy (XPS) study of copper resinate, a transparent green glaze that is coloured by copper salts of resin acids. This pigment was used in Europe in the fifteenth and sixteenth centuries, but it does not seem to be a usual feature of the palette anywhere after the end of the sixteenth century, because its tendency to discolour was already widely known by artists. An essential prerequisite for the restoration of works of art is the understanding of the effects of various climatic parameters on the deterioration process. For this reason, pictorial models of copper resinate in linseed oil, capable of simulating the ancient paintings on mobile supports, were prepared and aged in a climatic chamber, under different conditions such as exposure to UV radiations, humidity and different concentration of chemical pollutants (NO₂ and SO₂).All the samples were investigated by XPS and the data obtained were evaluated in order to estimate aging effects as well as mechanisms of degradation. On these paint layers damage induced by X-ray irradiation was also verified. PACS 79.60.-i; 61.80.Cb; 81.40.Cd