Evaluating the use of standoff LIBS in architectural heritage: surveying the Cathedral of Málaga

Abstract

Laser-induced breakdown spectroscopy (LIBS) is a cutting-edge technology which offers appealing features for its application in the field of the cultural heritage. It is a proven technology for the fast and simultaneous detection of major and trace elements with minimal destructiveness, using easily compactable instrumentation into movable platforms for the in situ and standoff chemical analysis of objects in real time. In the present work, a standoff LIBS sensor has been used for surveying the Cathedral of Málaga. The spectroscopic measurements were gathered in situ although from an averaged distance of 35 m. A comprehensive characterization of the materials composing the main façade as well as identification of the noticeable pollutants at their surfaces has been performed. The standoff LIBS results have fitted neatly with the mineralogical analysis of all the stones assayed. The large emissions of Si, Al, Ca and Mg have confirmed that the structure was almost entirely built using sandstone. In turn, the sensitivity to carbonate chemistry has demonstrated the capability of standoff LIBS for coherently classifying different marbles, thus allowing the identification of their origins. Standoff LIBS has also allowed the detection of pollutants such as Si, Ca, Mg, Fe, Al, Ba and Sr, originating from natural sources such as the transport of re-suspended dust and atmospheric particulate matter related to marine aerosols. In addition, trace elements such as Ti, Pb and Mn from exhausts of gasoline and diesel engines are also involved in the pollution triggering of materials. To obtain all these findings, scaffolding or other intrusive facilities have not been required.