From Raphael (La Deposizione) to Raphael (La Fornarina): a Circumnavigation Accompanying the Evolution of Energy-Dispersive XRF Devices

This paper describes history and technical evolution of portable devices which use energy-dispersive X-ray fluorescence (EDXRF)-analysis to study works of art. The history starts in 1971, when the first transportable equipment was employed to examine the pigments of Raphael's painting "La Deposizione" during restoration at the "Istituto Centrale del Restauro" in Rome. Then, paintings of all types were analyzed and metals (bronzes, brasses, gold and silver). The evolution of the exciting source is described (from radioisotopes or big size X-ray tubes, to miniaturized, dedicated X-ray tubes) and of X-ray detectors (from proportional gas counters, to N-2-cooled Si or Ge-detectors, to Peltier cooled HgI2 and Si-PIN, to Peltier cooled Si-drift). Also, the pulse height analyzers had an important evolution, from a heavy box to a computer card, to very small electronic circuits included in the detector box. The most "modern" portable EDXRF device is currently composed of a small-size X-ray tube, a Si-drift detector, both properly collimated, a portable computer, and dedicated software for the processing of the data. The total weight of such a device is about 2 kg. The last evolution: from analysis of a limited number of points to a complete scanning of the artifact. A mechanics is also required, with a sophisticated software interfacing mechanics to measuring heads. Maps giving the distribution of all analyzed elements in all areas of the painting "La Fornarina" by Raphael could be obtained. Finally, an accurate analysis of the K or L-X rays of the elements present in the paintings allowed to determine the disposition of the pigment in the correct layer.