X-ray analysis reveals composition hidden under iconic Lavoisier portrait


18th-century French chemist Antoine Lavoisier is a complicated historical figure. Scientifically, of course, he’s an undisputed giant, helping usher in the chemical revolution as the field has shifted from a qualitative to a quantitative approach, among many other accomplishments. He was also a wealthy nobleman and tax collector for the General Farm, one of the most hated bodies in Old regime as the French Revolution gained momentum. These activities added to his fortune, which he used to fund his scientific research (and that of others) and to promote public education. But that’s also why he clashed with the revolutionaries in power during the infamous Reign of Terror; they beheaded Lavoisier and his father-in-law on the same day in 1794 as “enemies of the people”.

Something of this complexity is evident in a new scientific analysis of the famous 1788 portrait, now in the Metropolitan Museum of Art in New York, of Lavoisier and his wife, Marie-Anne, by the neoclassical painter Jaques-Louis David. . The painting shows husband and wife posing with a collection of small scientific instruments, a tribute to their intellectual efforts.

But cutting-edge analytical techniques revealed that David had originally painted a different version, without the scientific props, describing the couple as more typical French aristocrats. He artfully masked the underlay in the final portrait, most likely in response to the growing backlash against the aristocracy, according to a recent article published in the journal Heritage Science. As the authors wrote in an article online for the Met:

In addition to changes to existing formats and popular poses in the 1780s portrait, the overall development of the Lavoisiers portrait moved away from highlighting their identity as tax collectors (the source of their wealth which allowed such a luxurious commission) and towards the enhancement of their scientific work. It is of course this latter identity which is so clearly defined today and which has contributed to perpetuate their fame both in the history of art and in the history of science. But another identity has been literally hidden in this portrait, and its revelation offers an alternate lens to apprehend Lavoisier not for his contributions to science but simply for a wealthy tax collector who could afford the whims of sartorial fashion. and the portrait which sent him to the guillotine in 1794.

Researcher Silvia A. Centeno acquires X-ray fluorescence maps of David des Lavoisier's portrait.
Enlarge / Researcher Silvia A. Centeno acquires X-ray fluorescence maps of David des Lavoisier’s portrait.

Antoine Lavoisier’s marriage to Marie-Anne Paulze, daughter of Jacques Paulze, colleague of the General Farm—was actually arranged by the father of the bride. Apparently, a much older earl wanted to marry 13-year-old Marie-Anne, and Paulze couldn’t categorically refuse without losing his job. So he persuaded Lavoisier, 28, to propose instead. Marie-Anne turns out to be an excellent choice and takes an active interest in her husband’s scientific work. She became an excellent laboratory assistant, sketching her experiments, translating English scientific texts into French and helping to maintain meticulous records of the procedures used. She was also a lovely hostess for the couple’s science evenings.

David was one of the most eminent painters of this period, just as renowned in his field as Lavoisier was in science. David gave private lessons to Marie-Anne Lavoisier, allowing her to sketch with precision the various experiences of her husband, and was the guest at the house of Lavoisier on several occasions. So naturally, the couple ordered him to paint their portrait. The finished product is considered a landmark of the neoclassical portrait. The Lavoisiers appear to be the very model of a “scientifically minded modern couple, dressed in a fashionable but simple dress, their bodies casually intertwined,” the authors wrote in their accompanying article.

The portrait of David is remarkably well preserved, which is perhaps why no one suspected the existence of an underlay until 2019, when the piece arrived in the laboratory of conservator Dorothy Mahon after quitting. ‘a curator noticed some degradation of the surface varnish. Before she could remove the varnish, Mahon had to analyze the paint very closely under a microscope to make sure that any mixture of solvents she used would protect the paint and not put her own health at risk.

It was then that she noticed chunks of red paint above Marie-Anne’s head and through the blue ribbons and knots in her dress. Mahon also noted dried cracks around the red tablecloth in the foreground of the painting. Obviously, a more in-depth analysis was warranted.

Elementary distribution maps acquired by MA-XRF on the portrait of Antoine-Laurent and Marie-Anne Pierrette Paulze Lavoisier: lead, (A);  mercury (B);  iron (C);  and calcium (D).
Enlarge / Elementary distribution maps acquired by MA-XRF on the portrait of Antoine-Laurent and Marie-Anne Pierrette Paulze Lavoisier: lead, (A); mercury (B); iron (C); and calcium (D).

SA Centeno et al./ Heritage Sciences, 2021

Like Silvia Centeno et al. point out in their paper, much of the technology used by this interdisciplinary team to examine the painting is fairly recent and would not have been available to them when the Met acquired the painting in 1977 from the Rockefeller Institute for Medical Research. First, the researchers used infrared reflectography (IRR) to scan the top layers of the paint. A specialized camera allowed the imaging of the entire nine-by-six foot canvas. The resulting reflectogram showed evidence of carbon-based black undershoot and dark and unclear shapes hinting at possible significant compositional changes.

Next, the researchers used macroscopic X-ray fluorescence imaging (MA-XRF) to map the distribution of elements in paint pigments, including the paint used below the surface. This process took around 270 hours and produced an enormous amount of data. It was Centeno’s expertise, complemented by chemical analysis of tiny paint samples, that enabled the team to create detailed elemental maps for further study.

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