A new model for XRF analysis of pigment layers

A new model for describing the X-ray autoabsorption in painting layers is presented. In it we take into account that the painting layer composition consists of small pigment grains embedded in a low Z binding medium. Accordingly, a linear law for autoabsorption inside the grains is assumed (due to the small size) and the X-Ray absorption in the medium is completely disregarded. The model developed is based on the fundamental parameter method entering as characteristic parameters of the sample: layer thickness, pigment grain volume and pigment grain volume density (dilution). We show by experiments, performed on Zinc and Lead white pigments, that in the thin layer approximation, good agreement with nominal values is obtained for the volume dilution.