Ilaria Costantini(1), Idoia Etxebarria(1), Iñaki Vazquez de la Fuente(1), Julene Aramendia(1), Gorka Arana(1), Irantzu Martinez(1), Juan Manuel Madariaga(1), Macarena Sanz(2), Lucía Pérez(3), Angel Yedra(3), Beatriz Yécora(4), Tamara Oroz(4).
(1) IBeA research group, University of the Basque Country UPV/EHU, Barrio Sarriena s/n 48940 Leioa, Spain.
(2) Garanza Rehabilitación S.L. C/ Laguna del Marquesado, 45A , 28021 (Madrid).
(3) Centro Tecnológico CTC, Parque Científico y Tecnológico de Cantabria (PCTCAN) c/ Isabel Torres nº 1. 39011. Santander (Cantabria)
(4) Lurrederra Centro Tecnológico, Industrial Area Perguita, C/A Nº 1 31210 – Los Arcos – Navarra – España
A multi-analytical investigation was carried out to evaluate the state of conservation of contemporary murals and trompe l’oeil painted by Alberto Pirrongelli, considered the greatest Spanish representative of this pictorial technique, on the facades of buildings in Navalcarnero (Madrid, Spain). Portable X-ray fluorescence, Fourier Transform Infrared and Raman spectroscopy were applied for in situ analysis of the original materials and the secondary product generated over the years. Successively, analysis with benchtop instruments (µ-EDXRF, Raman spectroscopy and ion chromatography) on selected samples, taken as a function of the in situ analysis, were performed to clarify some aspects.
The results revealed that all the wall paintings were made on a preparation layer of a mixture of rutile (TiO2), calcium carbonate (CaCO3) and an organic polymeric binder, probably polystyrene, mixed with a lower amount of dolomite (CaMg(CO3)2). The pigments used were identified, which include phthalocyanine green and blue, barium sulphate (the inorganic part of the lakes), arylamide yellow, hematite, carbon black, ultramarine blue and naphthol red.
The state of conservation of the murals was different as a function of the local environment. The most dangerous damage was in a mural that decorate a fountain. The swelling of the pictorial film, caused by the infiltration of humidity, due to the constant presence of water, and the consequent formation of salts efflorescences rich in Na+, K+, NH4+, Cl–, NO3–, y SO42-, caused the loss of the paint layer. They were characterized with Raman spectroscopy as gypsum (CaSO4·2H2O), thenardite (Na2SO4), potassium nitrate (KNO3), sodium carbonate (Na2CO3), generated by the influence of natural and anthropogenic (agriculture activities and a nearby highway) agents. In another mural a craquelure was shown on the pictorial film in some black areas, possibly caused by the contraction during the drying process of the polymers or an excess of paint used . In addition, one of the most evident degradation process appeared in another mural where the persistent dripping of water, through an iron grating, caused the formation of an iron red patina, composed by the iron(III) oxide hematite and an iron(III) oxi-hydroxide, in an extensive area of the mural, causing an important chromatic variation of the original green pigment.
 T. Rivas, E. M. Alonso-Villara, J. S. Pozo-Antonio, The European Physical Journal Plus volume 137, 2022, 1257.