Chemical and colorimetric analysis for the characterization of degradation forms and surface colour modification of building stone materials

Abstract Historical buildings of Catania city centre (Eastern Sicily, Italy) have been built for centuries using natural stone materials from local resources, including volcanic and carbonate rocks, matched in a peculiar bichromy. Particular attention is here paid on the carbonate rocks, which are generally more susceptible to decay processes. Such stones are sometimes covered by pigmented coatings with decorative purposes as well as protective function. In some cases, these nuances are partially or totally lost due to the decay processes which can also cause a modification of the chemical composition of the stone surface. The aim of this study is to prove the effectiveness of in situ X-ray Portable Fluorescence and colorimetric techniques for the characterization of degradation forms and colour modifications affecting several limestone-made historical buildings of the city centre of Catania. The results obtained, processed by means of multivariate statistical analysis, highlighted that all the stone surfaces exposed outdoor exhibit both chromatic and chemical modifications. In addition, three diverse types of superficial treatments have been identified, being related to different construction periods