Leonardo da Vinci is celebrated for his pioneering contributions in both the arts and sciences. A recent study in the Journal of the American Chemical Society has revealed that his penchant for experimentation wasn’t limited to his masterpieces’ surfaces but also extended to the foundational layers beneath them.
Interestingly, traces from iconic works like the “Mona Lisa” and “Last Supper” indicate that he dabbled with lead(II) oxide, leading to the formation of the uncommon compound plumbonacrite beneath his creations.
The composition of paints and hues in da Vinci’s workspace has long been a subject of intrigue, prompting researchers to delve into his notes and art for insights.
Many artworks from the start of the 16th century, the “Mona Lisa” included, were crafted on wooden canvases, necessitating an initial, robust “ground layer” of paint before the primary artwork was drawn.
Research reveals that while most artists of his era opted for gesso, da Vinci stood out, preferring dense coatings of lead white pigment and enriching his oil with lead(II) oxide. This orange tinted pigment imparted distinctive drying characteristics to the overlaying paint.
This innovative approach was also evident in the foundational layer of the “Last Supper”, distinguishing it from the prevailing fresco methods of the era. To delve deeper into these distinct layers, Victor Gonzalez and his team embarked on applying advanced, precise analytical methods to minuscule samples from the two renowned paintings.
Their examination focused on an inconspicuous “microsample” extracted from the “Mona Lisa” and 17 similar samples taken from various parts of the “Last Supper”. Employing X-ray diffraction and infrared spectroscopy, the team discerned that the paintings’ base layers consisted not just of oil and lead white but also included the seldom-seen lead compound: plumbonacrite (Pb5(CO3)O(OH)2).
This substance hadn’t been previously identified in art from the Italian Renaissance, although it was present in some of Rembrandt’s later 17th-century works. Plumbonacrite remains stable in alkaline settings, indicating its origin might have been a reaction between the oil and lead(II) oxide (PbO).
Unaltered PbO grains were also prominently found in most “Last Supper” samples.
While it’s known that artists incorporated lead oxides into hues to facilitate drying, this method remains unverified for da Vinci’s era artworks. Interestingly, upon perusing his notes, the team found mentions of PbO only in the context of treatments for skin and hair, despite its recognized toxicity.
Although not explicitly documented, these findings suggest that lead oxides were undeniably part of da Vinci’s artistic toolkit, potentially contributing to the creation of his timeless masterpieces.