Multianalytical approach for characterizing materials and pigments of Bizantine wall paintings in Hierapolis archaeological site (Turkey)

The study of fragments of Byzantine wall paintings regarding the Sanctuary of the Apostle Philip, in Hierapolis of Phrygia, one of the great Hellenistic, Roman and Byzantine cities of south-western Turkey (Pamukkale, Denizli Province), was carried out in the framework of the Marmora Phrygiae project financed by the Italian Ministry of University and Research (MIUR). The plasters decorated the Byzantine church with three naves built over the tomb of the Apostle. The archaeological investigations have recovered the fragments of plaster of the apses and the narthex. This study was firstly performed using a series of non-invasive techniques such as Ultraviolet (UV) fluorescence and Visible Induced Luminescence (VIL) belonging to the multispectral photographic techniques, Fiber Optic Reflectance Spectroscopy (FORS) and portable X-Ray Fluorescence (XRF) spectrometry applied on the fragments of mural paintings. This first set of measurements was conducted in situ at the storage of the Italian Archaeological Mission in Hierapolis where all the excavated materials were stocked. In this way it was possible to have a first characterization and to group by type all investigated fragments. Then, the most representative and interesting samples were sampled for further studies with laboratory techniques such as optical and electronic microscopy, FTIR and X-ray diffraction. The sampled fragments are made with a plaster mainly constituted by lime with straw without aggregate or lime with sand river aggregate. Moreover, it was possible, to observe one or more (up to three) layers of plaster. The pigments used were red ochres and, in few cases, minium for the red, lapislazuli or Egyptian blue for the blue, for the green a mixing of Egyptian blue and green earth, ochres for the yellow and carbon for the black.