Further investigations on limestone artifact surface modifications by laser-induced breakdown spectroscopy depth-profiling

In the context of the preservation of cultural heritage, it is relevant to study the degradation mechanisms of materials of which historical constructions are made. Limestone was one of the most widely used materials in many monuments exposed to urban aggressive atmosphere that affected its durability. In this work, a limestone sample was collected from the masonry blocks of an ancient jamb of the historic entrance gate of Castello Svevo, Bari, Italy. The choice was based on its evident degradation, i.e. a deposit of black crusts. The laser cleaning process combined with laser-induced breakdown spectroscopy (LIBS) analysis was applied to remove and then characterize the altered limestone sample. The elemental composition of the ablated black crust and the underlying stone were determined by spectroscopic analysis of the plasma emitted using a double pulse (DP) LIBS configuration. The limestone sample was also subjected to a depth-profile analysis of the black crust area and the laser cleaned zones in order to identify and analyze the decrease or disappearance with depth of specific elemental components.