Unveiling Portinari's palette: Multimodal analysis of São Jorge e o dragão mural and paint tubes

Abstract

Candido Portinari was one of the most important Brazilian modernist artists. He received national and international recognition and left a prolific legacy of over 5000 artworks. His work is distinguished by its vibrant color palette and the diversity of media and themes, ranging from murals and easel paintings to drawings on paper. In his works, Portinari portrays aspects of the work in the countryside and in the city, as well as sacred art. This study employed an integrated approach, combining spectroscopic (ED-XRF, Raman), imaging and computational methods, to analyze the “São Jorge e o dragão” mural painting. The collection of the artist’s preserved oil paint tubes, from the Museu Casa Portinari was analyzed by XRF and Raman. Results identified key pigments such as cobalt blue (CoAl₂O₄), ultramarine (Na₇ Al₆ Si₆​O₂₄​S₃), cadmium red (Cd(S,Se)), and Fe/Mn-rich browns (umber or burnt umber) in both the mural painting and oil paint tubes. Infrared False Color (IRFC) imaging further revealed a complex palette in the mural, distinguishing multiple brown mixtures and highlighting the use of ultramarine in blue areas. The application of computer vision, specifically image alignment using SIFT and an analysis based on the Structural Similarity Index (SSIM). This integrated approach deepened the understanding of Portinari’s work and established a robust methodology for the study of paintings in general within the field of cultural heritage sciences.