Raman And Fourier Transform Infrared Microspectroscopies Reveal Medieval Hispano-Muslim Wood Painting Techniques And Provide New Insights Into Red Lead Production Technology

This paper describes the study of two Nasrid polychrome wooden ceilings from the Alhambra monumental ensemble using vibrational spectroscopic techniques. The study is focused on the identification of the constituent materials and execution techniques used employing non-invasive and non-destructive scientific investigation methods. Information about both inorganic (pigments) and organic (binders and coatings) materials has been obtained without the need for time-consuming procedures. A complex stratigraphy involving the use of a protective priming layer of red lead covered with animal glue and white lead was revealed. The identification of Raman signatures of different lead oxide compounds, including lead-tin oxide (Pb2SnO4), in the priming layer, allowed us to hypothesize the synthesis of red lead (Pb3O4) from litharge (alpha-PbO), a common by-product of the cupellation process used since antiquity for silver production. Furthermore, the pigments employed in hidden drawings found in the reverse of the wood pieces of one of the ceilings were also studied and compared with those found in the visible external face.