A multi-technique approach, based on mobile/portable laser instruments, for the in situ pigment characterization of stone sculptures on the island of Crete dating from Venetian and Ottoman period

A versatile analytical methodology is presented, that combines the application of two mobile laser-based analytical techniques, Raman microscopy and laser-induced breakdown spectroscopy (LIBS), for the analysis of materials in historical and archaeological objects and monuments. In the present study, the proposed methodology was employed in the context of analytical campaigns aiming to investigate paint materials used on the island of Crete during the Venetian and Ottoman periods, thirteenth to nineteenth century CE. The first series of campaigns were conducted at the Historical Museum of Crete, Heraklion, Greece, and provided for the first time compositional data concerning the pigment palette used for painting Ottoman sculpture in Crete. In the second series, campaigns were performed outdoors for studying pigments in the sculptured door frames of two small medieval churches situated at rural locations in the greater Heraklion area. Raman and LIBS analyses gather complementary compositional data, molecular and elemental respectively, which, taken jointly, enable, in most cases, identification of pigments and accessory materials in paint layers, providing also stratigraphic information. With both instruments, measurements are performed directly on the surface of the objects or monuments, with no need for any sampling or sample preparation and thus analytical studies can be conducted rapidly and routinely in the context of a museum setting, a conservation laboratory or even outdoors. A standardized procedure that facilitates data collection and interpretation, interdisciplinary cooperation and presentation of results is adopted that optimizes the overall efficiency of the analytical campaigns.