The use of portable XRF systems for preliminary compositional surveys on large bronze objects: a critical review after some years' experience

The criteria with which X-ray fluorescence (XRF) is used to investigate large bronzes will probably undergo a substantial revision due to the miniaturization of the components and the consequent increased portability of the spectrometers. According to this point of view, some years ago the authors started using a portable spectrometer for non-destructive compositional surveys in which the possibility of absolute quantitative determinations was not even considered; the spectrometer was simply used to detect - not to measure - compositional differences among different parts of the object. This paper intends to take stock of the experience gained so far by referring to three large bronze objects, the Capitoline Horse, the central external door of St. Mark's Basilica in Venice and the colossus of the emperor Constantine. The XRF results are compared with those of atomic spectroscopy (ICP) by analyzing the two sets of data with the method of the principal components, the ICP data are also used to calculate the detection limits and resolving powers.