LIBS: A Powerful Analytical Tool for the Geochemical Diagnostics of Stone Artifacts

The geochemical fingerprinting of stone artifacts based on mineralogical, petrographical and isotopic data can provide unique information on the geological and geographical origin of materials and help to reconstruct material pathways from sources to artifacts and determine the possible nature and causes of alteration, so providing useful operational guidance for their preservation, restoration and conservation. In particular, for the preservation and restoration of historic buildings, it is essential to characterize the construction and mortar materials, determine their origin, and analyze in detail their alterations. The improved efficiency and tremendous developments in the analytical capabilities of novel advanced non­invasive, nondestructive or micro­destructive spectroscopic and imaging diagnostic techniques occurred in the last decades have improved enormously the characterization and discrimination of materials and weathering products, so contributing substantially to improve the traditional conservation and restoration approaches with relevant innovation in cultural heritage research providing new solutions and perspectives. In the last two decades, a number of analytical techniques, including elemental and isotopic analyses, Raman, infrared and laser­induced breakdown spectroscopy (LIBS) and Xray fluorescence (XRF), have been widely used with increasing frequency and variable success in cultural heritage research to identify the major and trace elemental and isotopic composition of stone materials and classify and discriminate them on the basis of their compositional profile of minor and/or trace elements fingerprinting. In particular, LIBS appears an ideal, fast, standoff method to measure a wide variety of elements, including those lighter than silicon (not possible by XRF), which can be employed in a variety of geometries with various distances from the target. Furthermore, the capacity of LIBS to operate in situ makes it particularly attractive for the analysis of large objects, monuments and historical buildings, where the use of mobile or remote sensing instruments offers significant advantages. The four features that distinguish LIBS from traditional laboratory­based analytical techniques are: no or minimal sample preparation requirement, capacity of analyzing both 20­100 ?m diameter spots and wholerocks, providing a LIBS spectrum containing a detailed chemical signature of the sample, and availability of backpack portable and handheld instrumentations that can be used directly in situ as a diagnostic tool not only for stone identification and analysis but also for depth profiling of encrustation grown on stonework and the distribution of environmental pollutants within it. Currently, the availability of reliable analytical instrumentation that can operate directly on site, such as handheld (h) LIBS, is in high demand. The fast data acquisition and minimal sample preparation features of these devices make them very attractive candidates for qualitative and semiquantitative elemental analysis, microchemical mapping and sample selection. Finally, the above­described advantages are expected to facilitate decisions concerning the planning and implementation of restoration treatments. In this presentation the basics of the LIBS technique for geochemical analysis will be summarized and recent results by various research groups of LIBS applications to mineral chemistry, geochronology and chemical mapping of cultural heritage stone artifacts will be discussed. In particular, the promising role and performance of hLIBS devices for the real­time, on site, routine chemical analysis of a broad spectrum of cultural heritage artifacts which is as yet only minimally explored, will be illustrated while targeting specific questions of geological interest.