Damage induced by proton irradiation in carbonate based natural painting pigments

Abstract The so called “dark spot” phenomenon produced during proton irradiation of pigments is an important factor to determine experimental conditions of ion beam analysis of pigments in paintings, miniatures, pottery and other art objects. Recently it has been suggested that this phenomenon could be due to the formation of colour centres during irradiation, but there is scarce knowledge about the characteristics and the reversibility of the damage. In this work a representative set of natural carbonate minerals, traditionally used as pigments, were exposed to proton irradiation in an external beam set-up, in order to simulate routine external proton induced X-ray emission (PIXE) analysis conditions of an art object. During irradiation ionoluminescence (IL) combined with PIXE were employed to identify the microscopic processes involved in the proton damage. After irradiation, two well-established techniques for the study of colour centres, thermoluminescence (TL) and optical absorption were used. Particularly, TL is a very sensitive technique to detect very low concentrations of radiation induced defects.