Challenges of analytical methods for the characterization of microsamples from David Alfaro Siqueiros mural painting

Our plain-English summary of Challenges of analytical methods for the characterization of microsamples from David Alfaro Siqueiros mural painting, by A. Mejía-González, Y. Jáidar, P. Aguilar-Rodríguez, et al (Analytical and Bioanalytical Chemistry, 2025).

The study

• Authors: A. Mejía-González, Y. Jáidar, P. Aguilar-Rodríguez, S. Zetina, N. Esturau-Escofet
• Journal: Analytical and Bioanalytical Chemistry
• Published: 2025;417(1):143-154
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This study presents the analysis of seven microsamples from Untitled Mural 3, painted by David Alfaro Siqueiros between 1964 and 1972. The mural has never been restored, therefore preserving the materials used by the artist. The microsamples were analyzed using a combination of techniques: optical microscopy (OM), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), micro-Fourier transform infrared spectroscopy (micro-FTIR) with reflection mode, and high-resolution nuclear magnetic resonance (NMR) spectroscopy. In this work, compounds common to those identified in the analysis of the contemporary mural Trazos de composición piramidal composition were identified, such as acrylic and nitrocellulose binders, titanium white and iron red oxide as pigments, and DEHP as a plasticizer. Unexpectedly, polyvinyl acetate (PVAc) and different nitrocellulose monomers were identified, in addition to chrome yellow instead of ochre, and a predominance of quartz, asbestos, and talc as fillers, instead of carbonates. The study confirmed that Siqueiros used multiple binders in successive layers in no apparent order, providing valuable insights into his artistic techniques. The research also proved an efficient methodology for studying very small and complex samples.

© 2024. The Author(s).

In plain English

This laboratory study analysed seven paint microsamples, each 0.5 to 1 square centimetre, from Untitled Mural 3 by David Alfaro Siqueiros. The mural is made of asbestos cement panels in steel frames and had never been restored, though it was fumigated. The study examined painting materials, not people. The authors used microscopy, elemental analysis and infrared spectroscopy to examine the paint layers one by one where possible. They used nuclear magnetic resonance spectroscopy on dissolved fragments containing several layers. Nitrocellulose, several acrylic compositions and polyvinyl acetate (PVAc) were found as binders in all samples, with PVAc mostly in layers near the surface. They also found the plasticizer DEHP and pigments including titanium white and iron red oxide; the yellow was proposed to be chrome yellow. Silicate fillers in thick layers near the panel, usually with nitrocellulose lacquers, were identified by their structure and composition as asbestos particles. The article did not name the asbestos fiber type. The authors concluded Siqueiros used nitrocellulose until the 1970s, mixed with asbestos fillers in ground layers. They also concluded that about 1 mg of sample allowed reliable characterization.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory materials analysis of paint microsamples from an art work (no human subjects), using optical microscopy, SEM-EDS, ATR-FTIR, micro-FTIR and NMR spectroscopy
• Who was studied: Seven microsamples (0.5 to 1 square centimetre each) from two stored panels of Untitled Mural 3 by David Alfaro Siqueiros. The mural measures 9.60 m by 19.79 m and has 36 panels. It was painted at his workshop La Tallera in Cuernavaca, Morelos, Mexico. It had never been restored, though a footnote documents a fumigation.
• Exposure: No human exposure was studied. The materials analysed were the paint layers (binders, pigments, plasticizers and fillers, including asbestos) on a mural support of asbestos cement panels. The asbestos fiber type is not named.
• Main results:
  • Electron microscopy identified asbestos fibers as particular microstructures in some paint layers, along with diatom micro skeletons and amorphous fillers.
  • Silicate fillers in very thick layers near the support, almost always associated with nitrocellulose lacquers, were identified as asbestos particles from their microstructure and composition.
  • Nitrocellulose, different acrylic compositions and PVAc were identified as binders in all samples. PVAc was almost always in the layers closer to the surface.
  • Pigments identified were titanium white, iron red oxide and possibly carbon black. Chrome yellow was proposed for the yellow pigment because sulfur, chromium and lead were detected.
  • NMR was performed on dissolved fractions of the multilayered microsamples, so it analysed mixed material from several layers rather than individual layers.
  • NMR distinguished two nitrocellulose monomers. The authors said these may indicate two distinct painting formulations, batches or brands. DEHP was the only plasticizer detected.
• The authors' conclusion: The authors concluded that Siqueiros used nitrocellulose until the 1970s, mixed with asbestos fillers in ground layers, and applied different binders with no consistent order. They proposed a method for reliable characterization from about 1 mg of sample.
• Limitations the authors state:
  • ATR-FTIR spectra could not be acquired from the back side of samples 2 and 6 because of residues of the support panel.
  • Micro-FTIR analysis was not possible for the discontinuous white 5-I and black 5-II layers.
  • In some samples the NMR signals of the components could not be identified.

Topics

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Infrared Spectroscopy (IR), Talc.

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