Unraveling Leonardo's Techniques: Elemental Analysis of The Last Supper

A cross-section micro-sample from The Last Supper mural painting, previously removed during research, was re-examined using a SEM equipped with the XFlash^® FlatQUAD detector.This advanced analytical technique allows for detailed chemical analysis, even in the presence of complex mixtures. The objective is to identify the main components of the cross-section, providing insights into Leonardo's painting process and any adaptations made during its creation The SEM analysis with the XFlash^® FlatQUAD successfully identifies the main components of the cross-section, revealing clues about Leonardo's artistic process. 

The SEM analysis using the XFlash^® FlatQUAD detector offers valuable insights into the chemical composition of The Last Supper mural painting, enhancing our understanding of Leonardo da Vinci's innovative painting techniques. By unraveling the secrets of this masterpiece, we gain a deeper appreciation for Leonardo's artistic genius and his enduring legacy in the history of art. Similarities in chemical composition between overworked areas suggest that Leonardo made repeated adjustments to the final painting. Moreover, the application of advanced analytical techniques contributes to the conservation and preservation of this cultural treasure for future generations to admire and study.

In essence, the SEM analysis with the XFlash^® FlatQUAD has not only enriched our understanding of The Last Supper but also underscored the significance of employing cutting-edge technology in art conservation and research. As we continue to unravel the mysteries of this iconic artwork, we embark on a journey to preserve and celebrate Leonardo's legacy for generations to come

Fig 1: The wall painting of The Last Supper was created by Leonardo for the Refectory of Santa Maria delle Grazie in Milan between 1494 and 1498.

Fig 2: Optical light image of the cross-section sample (mounted in epoxy). Bottom to top: (1) Initial gesso layer, (2) Initial red paint layer, (3) second gesso layer, (4) various red paint layers of the final depiction and (5) retouch.

Fig 3: Two working stages in optical light image, are visible, the red painting area, from which the sample was removed, was reworked. 

Was this done by Leonardo himself? 

To solve this question, the material of the first and second working stage were investigated using the XFlash® FlatQUAD and the chemical information from EDS measurments compared.

Fig 4: Compared areas and related spectra of the two white ground layers showing similar spectra.

A high-resolution mapping of the ground layer reveals the variety of materials present. The presence of Ca and Mg indicates the use of a dolomitic limestone. Additionally, lead white (2PbCO3·Pb(OH)2) admixtures are present. 

Fig 5: Comparing the composition of the discarded red paint in between the white ground layers and the final red painting likewise shows similarities between the pigments used. Measurement conditions: 12 kV, 8 µs pixel time. Overall time: 12 min.

Fig 6: Mapping and spectra of the pigments.

Multiple elements present in the red paint layers show the complex mixtures of different pigments: Pb signals can be related to either lead white or lead oxides. The high content of Fe interlinked with Si, K, Al and Mn can be ascribed to a red ochre of a natural source..

Fig 7: Red ochre-related elements.

Al-, K- and P-rich phases further indicate the presence of a red lake that was applied to create the translucency.

Elemental markers for lakes correlate with a pinkish layer fluorescing under UV illumination. This fluorescence as well as the identification of Al, P and K hint at the insect origin of the lake (like Kermes).

Fig 9: High-resolution mapping of a detail and point measurement aid the identification of  the lake used.

Fig 8: Mapping and spectra of the pigments.

Hyperspectral imaging provided by the XFlash® FlatQUAD detector has invaluable insights into the chemical composition of The Last Supper mural painting, contributing significantly to our understanding of Leonardo da Vinci's innovative painting techniques. The absence of an intermediate lead layer challenges conventional wisdom regarding the use of lead in preparatory layers, highlighting the importance of empirical analysis in art historical research.

The use of the XFlash® FlatQUAD enabled the identification of main components within the cross-section, despite the presence of complex mixtures. Its fast scanning speed, coupled with low beam currents and short measurement times, demonstrated the efficacy of this advanced analytical tool in characterizing historical artworks with precision and efficiency. The XFlash® FlatQUAD has not only enriched our understanding of The Last Supper but also underscored the significance of employing cutting-edge technology in art conservation and research.