Characterisation of the transparent surface coatings on post-Byzantine icons using microscopic, mass spectrometric and spectroscopic techniques

Icons are frequently covered with superimposed transparent layers of varnish and glaze that often obscure their image and disrupt their study and conservation treatment. Using a combination of microscopic, mass spectrometric and spectroscopic techniques, a micro-analytical methodology was developed for the characterisation of these surface coatings. More specifically, light microscopy (LM), electron ionisation direct temperature resolved mass spectrometry (EI-DTMS), pyrolysis gas chromatography mass spectrometry (Py-GC/MS), imaging Fourier transform infrared spectroscopy (imaging-FTIR) and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX) were used to investigate the coatings present on the surface of five Greek post-Byzantine icons. The results showed that the aged layers of varnish and glaze contain various mixtures of materials, including diterpenoid (DTP) and triterpenoid (TTP) resins, linseed oil, lead-containing dryers, egg, and beeswax. This study also elucidated issues regarding the initial application and the later interventions on those coatings, their interaction with each other, as well as some effects observed on the underlying paint layers.