Comparison of three portable EDXRF spectrometers for pigment characterization

The identification of pigments used in the paint layers of works of art is important when dealing with issues regarding conservation and restoration, and also when studying the techniques of artists. Various standard, non-invasive techniques are available for those purposes, each with its specific limitations, such as Raman spectroscopy (micro-Raman) [1], micro X-ray fluorescence (micro-XRF) [2], infrared [3] or visible reflectance spectroscopy [4]. EDXRF, in particular, is a very suitable tool for examination of paintings, widely used thanks to its relative straightforwardness of use and its totally non destructive character, allowing for analysis without any sample preparation [5]. In recent years, a number of portable and handheld EDXRF spectrometers became commercially available, each with its own distinguishing features and fields of application. The diversity of designs and features of these instruments makes it sometimes difficult to compare results obtained with different XRF systems, especially during in situ investigations. This prompted us to perform a systematic comparison of three commercially available spectrometers used the most in archaeometric analyses. Spectrometers were chosen according to their different characteristics in detectors, weight, software, maintaining as a common feature the Mo target of X-ray tube. In fact, Mo (EK-? = 17.4 keV) target is usually preferred in respect to others (such as W or Ag, for example) because its X-ray lines do not overlap with X-ray lines of elements present in constituent materials of ancient objects. The main part of the analyses was conducted on pigments in laboratory tests, then a number of measurements was also made in situ, in order to evaluate the portability and the convenience of use of each instrument.