LIBS and XRF analysis for a stratigraphic study of pictorial multilayer surfaces

The study of painting materials is a primary goal for the historical and artistic characterization of works of art because it provides useful information about the original materials and their degradation products, the painting technique and any conservation treatments. However, the archaeometric investigations are very complex because the need to safeguard the Cultural Heritage makes necessary the use of non or micro invasive techniques. Among the possible analytical approaches, Laser-Induced Breakdown Spectroscopy, supported by X-ray Fluorescence spectroscopy for a faster elements identification, allows stratigraphic analysis with high spatial resolution enough to discriminate different pictorial layers. Moreover, an integrated approach based on the above techniques is particularly useful for the complementarities of the outcomes (in terms both) of investigated thicknesses and detectable elemental content. This paper aims to validate, in the archaeometry field, the use of Laser-Induced Breakdown Spectroscopy for stratigraphic investigation of painted surfaces/objects by means of analytical results obtained from original fragments of mural paintings originating from different sites and artistic eras. Indeed the focus of this work is to determine the optimum parameters for LlBS technique in order to acquire the maximum information with the least damage to the works of art. The results concern mainly the comparison between the identification of the chemical elements by using the more traditional X-Ray Fluorescence technique and the study of their distribution along the thicknesses of the paint layers from the Laser-Induced Breakdown Spectroscopy analyses. The collected data have demonstrated the usefulness of the Laser-Induced Breakdown Spectroscopy investigation, through which it has been possible to reveal chemical elements undetectable by X-ray Fluorescence spectroscopy and to analyse the stratigraphic sequence of paint layers from the surface up to the preparation layer. Furthermore, they have provided good insight into the different painting layers by confirming the potential of the Laser-Induced Breakdown Spectroscopy to carry out stratigraphic analyses in a micro destructive way.