Learn how da Vinci's most famous masterpiece is playing her part in helping researchers uncover the materials and techniques used in her creation—with the assistance of X-ray and infrared techniques.

Everyone has heard of the Mona Lisa, even if they haven’t jostled in the crowd at the Louvre for a glimpse of her enigmatic smile. Painted some time between 1503–1519, she is one of fewer than 20 remaining works of Leonardo da Vinci—a piece of the enduring puzzle and interest that surrounds this great master and thinker of the Italian Renaissance.

da Vinci's interests spanned numerous disciplines that we would recognize today as chemistry, engineering, physics, mathematics, and zoology. He has been credited with ideas and inventions far ahead of his time, and his artistic works are no less extraordinary, refusing to fit within the accepted practices of the time.

In particular, work has shown that the buildup and materials used in each of da Vinci’s paintings is different, especially in the thick layer between the wooden panel and the final image. Previous X-ray imaging revealed a radio-opaque, thick paint layer under the Mona Lisa’s surface.1 In other da Vinci paintings, art historians and chemists have identified different materials in this preparatory layer from water-soluble glue, gypsum, and lead white, to orange oil mixed with white and red lead.

Some believe these differences could be due to the way the boards were prepared, with larger panels perhaps coming pre-primed from a carpenter and others made by hand from unfinished planks.1 Now, research published in the Journal of the American Chemical Society is painting a new picture using X-ray and infrared microanalyses.2

Victor Gonzalez and colleagues used synchrotron radiation high-angular resolution X-ray powder diffraction (SR-HR-XRPD) and micro Fourier transform infrared spectroscopy (μ-FTIR) to gather new clues on the Mona Lisa’s ground layer, and they discovered an uncommon composition. Investigation of a minuscule paint fragment revealed the presence of a plumbonacrite—a compound that the team had previously detected once in a fragment from a van Gogh painting, and more recently in some Rembrandt works—but never before in anything from the Italian Renaissance.3-5 Since this rare lead carbonate is stable only in an alkaline environment, it could have resulted from chemical reactions involving an alkaline lead compound, such as types of lead oxide commonly used as a drier.

Watch a video surrounding this research created by the ACS Science Communications Team:

;

Gonzalez and his team have previously published work in Analytical Chemistry on how to determine the origin and history of lead-white pigments by their photoluminescence properties,6 giving art historians a way to fingerprint the materials that make up famous and valuable paintings. This further analysis supports the use of a highly saponified oil containing lead soap for the ground layer behind the Mona Lisa. The authors took these chemical findings and reviewed da Vinci’s manuscripts, looking for clues about historical use from known compound names: litharge for a tetragonal, orange-red form of lead oxide stable at room temperature, and massicot for the orthorhombic, yellow high-temperature form—but both terms also have other meanings. Nevertheless, da Vinci’s texts mention letargirio di pionbo as a skin and hair remedy, suggesting he had access to the compound for pharmaceutical uses, and may have repurposed it for artistic experiments. And the term macicot or masticot are used in a recipe for how to prevent decay in a painting from decay and to “preserve it always fresh and unfaded”.2

Taken together, these findings help shed light on the old master’s palette and add a new dimension to our appreciation of the small but perfectly formed Mona Lisa.

References

  1. Ravaud, E. et al. L’art de la matière; L’art et la manière, Léonard de Vinci, 2019; pp 358–369.
  2. Gonzalez, V. et al. X-ray and Infrared Microanalyses of Mona Lisa’s Ground Layer and Significance Regarding Leonardo da Vinci’s Palette. J. Am. Chem. Soc. 2023, 145, 42, 23205–23213.
  3. Gonzalez, V. et al. Composition and microstructure of the lead white pigment in Masters paintings using HR Synchrotron XRD. Microchem. J. 2016, 125, 43–49.
  4. Gonzalez, V. et al. Unraveling the Composition of Rembrandt’s Impasto through the Identification of Unusual Plumbonacrite by Multimodal X-ray Diffraction Analysis. Angew. Chem. Int. Ed. 2019, 58, 5619.
  5. Gonzalez, V. et al. Lead (II) Formate in Rembrandt’s Night Watch: Detection and Distribution from the Macro-to the Micro-scale. Angew. Chem. 2023, 135, e202216478.
  6. Gonzalez, V. et al. Revealing the Origin and History of Lead-White Pigments by Their Photoluminescence Properties. Anal. Chem. 2017, 89, 5, 2909–2918.

Want the latest stories delivered to your inbox each month?