The investigation of ancient metal artefacts by portable X-ray fluorescence devices

X-ray fluorescence (XRF) analysis by portable spectrometers has long been applied to the study of ancient metal artefacts. On one hand, its effectiveness depends on its ability to provide answers to archaeological, historical and technological questions. On the other hand, the artistic and monetary value of artefacts requires mandatorily respecting the physical integrity of the objects in most cases. These two conditions - i.e. being non-destructive and, at the same time, capable of significant results - affect the designing of spectrometer, with special attention given to the balance between portability and analytical performance, as well as measurement strategy. This paper presents a critical discussion concerning the use of portable XRF devices in the investigation of ancient metal artefacts, including the advantages and limitations of different technical solutions and measurement strategies. Measuring the absolute composition of the objects often requires the removal of the patina, which is seldom permitted for ancient artefacts. Hence, emphasis is given to alternative methods that are more respectful of artefact integrity and are able to make the most of the non-destructivity and measurement speed, which are the real mainstays of portable XRF. Other uses of this technique such as the analysis of multilayered materials and the study of surface compositional changes are also discussed.