Microbiological and compositional features of green stains in the glaze of the Portuguese “Great View of Lisbon” tile panel

Abstract

© 2015, Springer Science+Business Media New York. The “Great View of Lisbon” is one of the most remarkable blue-and-white Portuguese tile panels, which depicts the city before the tragic earthquake of 1755. This panel presents visible colored alteration in the glaze of tiles both from the exhibition and the depository of the Museu Nacional do Azulejo (Portugal). This work is a contribution to identify the origin of green stains in the glaze by using microbiological techniques, scanning electron microscopy with back-scattered electron imaging (SEM-BSE), Raman spectroscopy, and proton-induced X-ray emission (PIXE). The microbiological assays showed that the filamentous fungi were detected only at a frequency <10 % of the microbiota of tiles surface, and the microbial entities from the green stains cultures were identified as Aspergillus fumigatus by molecular biology techniques. However, no microorganisms or other biological elements were found by SEM-BSE in the green stains. Raman spectroscopy and PIXE results showed that the green stains appear to be related with the presence of chromium atoms in the outer part of the glaze. Eskolaite, a “green pigment” used before 1850 AD was clearly identified by Raman spectroscopy in the darker green stains. Nevertheless, no chromium oxide signatures were identified in the lighter green stains by Raman spectroscopy.