Multi-analytical investigation into painting materials and techniques: the wall paintings of Abuna Yemata Guh church

Abuna Yemata Guh is one of the nine Saints who are traditionally claimed to have come to Northern Ethiopia in the beginning of the sixth century and established monasteries in the Tigray region. The church, named after him, is hewn out of the side of one of the highest sandstone spires in the Gheralta area. Though the local tradition claims earlier dates, the paintings in the church are suggested to belong to the second half of the fifteenth century on the basis of their theme, style and iconography. We report here the investigation into the materials and techniques of the paintings using diverse complementary analytical techniques: Polarized light microscopy (PLM), portable X-ray fluorescence spectrometer (pXRF), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), synchrotron-based X-ray diffraction (SR-XRD), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS), micro-Raman spectroscopy (MRS) and micro-Fourier transform infrared spectroscopy (micro-FTIR). Earth materials based on hematite, goethite and terra verte were the main findings, but cinnabar, orpiment, lead white and carbon black were also identified. The stratigraphic analyses of samples from different locations coupled with SR-XRD analysis indicated the presence of anhydrite, gypsum, calcite and lime in the preparation layer. The pigments identified together with close visual examination showed repainting and retouching within the area in which the Marian figure is depicted, as well as in a nearby figure. The ground preparatory layer consisted of red mud reinforced by straw applied to the chiseled sandstone support. The egg-based binding medium suggests that tempera technique was used. Technical studies of Ethiopian wall paintings are scant, but highly needed as this world heritage is threatened due to limited conservation. Our documentation of the materials and techniques is therefore aimed to stem this loss, as well as to provide information for art historical studies.