An insight into the green deteriorated paint layers of the maritime station of Alcântara (Lisbon) : an archeometric study

This study reports the first results of the analysis carried out in 2022 on deteriorated green paint layers from the mural paintings made by Almada Negreiros at the Maritime Station of Alcantara, in Lisbon (Portugal). These murals painted in 1945 are one of the most emblematic painting sets done by the modernist artist and exhibit a bright chromatic palette that displays different states of conservation, with the green paint layers particularly damaged, showing severe flaking and powdering in the lightest shades.To understand the decay phenomenon, in-situ and laboratory analyses were done in an attempt to identify the green chromophores, the painting technique, and the decay agents causing the visible degradation. The analytical setup comprised in-situ technical photography (Vis, Vis-Rak, and UVF), handheld optical microscopy (h-OM), handheld energy dispersive X-ray fluorescence (h-EDXRF), colorimetry, and spectrophotometry in the visible light range. Microsamples of selected paint layers from deteriorated and stable green areas were collected and further analysed in the laboratory by optical microscopy in visible and ultraviolet modes (OM-UV-Vis), variable pressure scanning electron microscopy coupled with energy dispersive spectrometry (VP-SEM-EDS), micro-X-ray diffraction (mu-XRD), micro-Fourier -transform infrared spectroscopy (mu-FT-IR) and micro-Raman spectroscopy.Results show the presence of both natural and industrial synthetic organic pigments, such as green earths and PG8, used alone or in mixtures with other chromophores (e.g., Fe-based yellow and red pigments, bone and carbon black, ultramarine blue, and the synthetic green PG1 and the yellow PY1). Concerning the decay phenomena, the main hypothesis for the powdering and flaking of the green paint layers is the activity of calcium sulphates (e.g., gypsum), which probably originated from both intrinsic and extrinsic sources and whose presence was found to be widespread in all the microsamples analyzed.