Are they fresco paintings? Technical and material study of Casas Pintadas of Vasco da Gama house in Évora (Southern Portugal).

The present paper describes the characterization and comparative study carried out on the 16th century murals of Casas Pintadas of the so-called Vasco da Gama House in the town of Évora, Southern Portugal. Even today, the two existing paintings in the porch vaulted cloister raise many questions about the pictorial techniques and materials that were used. The most adopted theory is that the upper register inspired in medieval bestiary was made with a secco technique, while the lower grotteschi frieze was achieved with a fresco technique. A multianalytical research was carried out in situ and in laboratory in order to attest this hypothesis and to characterize the paintings materials. Surface examination was made with normal and racking light complemented with in situ spectrophotometry in the visible, with stratigraphic and analytical study of microsamples by optical microscopy (OM) and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDS). The results show similarities in the structure and elemental composition of both paintings mortars and pigments. The mortars' inner layers (the intonaci) were made with siliceous sands mixed with a dolomitic lime-based plaster (CaMg(CO₃)₂). On top of it, one to three thin layers of lime wash were applied. In SEM-EDS elemental maps, all the pigments at the cross-sections are embedded in a calcium carbonate matrice, and several nails marks are visible in situ with racking light in both paintings indicating a fresco technique. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]