Microanalytical investigation of degradation issues in Byzantine wall paintings

The St. Euthymius wall paintings, in the Cathedral of Thessaloniki, dated 1303 AD., are stylistically attributed to the School of Panselinos, one of the most important painters of Palaeologean Art. An in situ non-invasive study has been carried out as part of a MOLAB project (a mobile laboratory accessible through the Eu-ARTECH project, funded by the EC 6th FP) combining different analytical techniques such as XRF, mid-FTIR and UV-vis diffuse reflectance spectroscopy. It was during this comprehensive in situ study that certain scientific queries were raised about sensitive areas, where indications of the phenomena of decay requested further attention. A subsequent laboratory study of selected cross-sections using microscopic analysis with mu FTIR, SEM-EDS and mu Raman, further confirmed the identification of only the atypical in situ observations. The comparative interpretation of all respective results on the specific regions of interest permitted the identification of several degradation phenomena which justify certain aesthetic or stylistic incoherences in the representations. Namely, (i) thermal dehydration of the yellow ochre explaining the reddish appearance of the flesh tones and halos as an accidental effect of the fire; (ii) thermal degradation of azurite converted to tenorite explaining the atypical instance of dark lightings on the purple garments; (iii) degradation of red lead employed in the lightings of the red garments; (iv) widespread presence of oxalates in the paint surface.