RESUMO
During the 20th century, modern painters experimented with different mediums and painting techniques, one of them was Rafael Coronel in his mural painting, Paisaje Abstracto (Abstract landscape). The painting was created with a peculiar pouring technique and an unknown binding medium; ageing produced fractures and severe conservation problems. Therefore, the characterization of the painting medium became an urgent matter in order to understand the current condition of the painting and to develop a proper treatment. The aim of this research was to characterize the chemical composition and painting technique of Paisaje Abstracto. To approach this goal two microsamples were taken and analyzed by optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), nuclear magnetic resonance (NMR) spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), micro attenuated total reflection Fourier transform infrared spectroscopy (micro-ATR-FTIR) and gas chromatography/mass spectrometry (GC/MS). The analysis allowed for the identification of cadmium sulfide (CdS) and titanium dioxide (TiO2) as inorganic pigments; aluminosilicate fillers; poly(methyl methacrylate) (pMMA) as a binder; MMA monomer, red organic pigment PR181; benzoyl peroxide, dibutyl phthalate and 1-octadecanol as organic additives. This study presents an innovative painting technique with pMMA, a medium not commonly used by artists, which was probably polymerized onto the painting support.
RESUMO
This study presents the use of high resolution Nuclear Magnetic Resonance (NMR) as an outstanding tool for identifying with accuracy the structure of the polymers used as binders and the additives used as plasticizers in samples from a mural painted by David Alfaro Siqueiros between 1964 and 1972, an important period in which his artistic production has not been previously studied. Additionally, the presence of some organic pigments was detected. The mural Trazos de composición piramidal currently located outside of Siqueiros' studio La Tallera, in Cuernavaca Morelos (Mexico) was an artistic experiment done by Siqueiros to test outdoor painting. Eight micro-samples of paint were thoroughly analyzed by Optical Microscopy (OM), Scanning Electron Microscopy - Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Fiber Optics Reflectance Spectra (FORS), Transmission Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance mode (FTIR-ATR) and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). Through these studies, contrasted with an historical investigation, we demonstrate that the samples present a multi-layered and complex painting system because Siqueiros made at least two versions of the painting. The multi-layered structure and the variable composition of each layer challenged the application of several analytical methodologies traditionally used for cultural heritage materials. In one sample, each layer was separated and they were studied in detail by FTIR-ATR, Py-GC/MS and NMR. This study revealed the presence of two main binders: acrylics in the first layers and nitrocellulose in the last one, also some phthalates and fatty acids were detected as additives. Inorganic pigments and fillers were identified as titanium dioxide and iron red oxide as well as diatoms and carbonates. The main contribution of this study, where NMR spectroscopy was applied for the first time in modern mural painting analysis, is the characterization of the materials used by Siqueiros during the last years of his artistic production.