The Secret Compound Leonardo da Vinci Used for Painting the Mona Lisa

The Ever Smiling Mona Lisa

‘Mona Lisa’ is one of the most revered paintings from the Italian Renaissance era. It is said to depict Lisa del Giocondo, the wife of a Florentine silk merchant. Even five centuries after the Italian noblewoman’s alluring beauty was immortalized in the painting through Leonardo da Vinci’s painting technique, many mysteries still surround it.

The Journal of the American Chemical Society solved one such mystery in October 2023 when it published a study that suggested da Vinci might have been in an experimental mood when he painted ‘Mona Lisa.’ 

Upon re-examining the canvas with modern tools, the researchers found something unique about the paint used for ‘Mona Lisa.’ They discovered the compound plumbonacrite in the first layer of paint. This fascinating discovery proves that Leonardo da Vinci’s painting technique involved more than artistic genius and often blended scientific rigor with creative experimentation.

Pigments used in the painting of Mona Lisa

Rediscovering Leonardo da Vinci’s Secret Paint Recipe for ‘Mona Lisa’

Led by Université Paris-Saclay scientist Victor Gonzalez and France’s National Center for Scientific Research, a team of scientists analyzed a microscopic sample—no larger than a human hair—taken from a hidden spot at the top right corner of the ‘Mona Lisa.’ 

Back in the 1500s, painters needed to add a thick ground layer of paint on the wooden panel before laying down their artwork. Most painters resorted to gesso for this purpose, but Leonardo da Vinci made an exception more than once. The scientists claimed that da Vinci mixed lead(II) oxide in the oil he used for the ground layer of these paintings. Lead(II) oxide is an orange pigment known to have significant drying properties. 

To analyze these samples further, the scientists used high-angle synchrotron X-ray diffraction and infrared spectroscopy. Besides oil and lead white, they also found a rare lead compound known as plumbonacrite (Pb₅(CO₃)O(OH)₂) in the base layer of these paintings. 

Victor Gonzalez, the lead author of the study, told Associated Press in an interview:

“In this case, it’s interesting to see that indeed there is a specific technique for the ground layer of ‘Mona Lisa.’ Plumbonacrite is really a fingerprint of his recipe. It’s the first time we can actually chemically confirm it.”

Interestingly, this compound had been detected in Rembrandt’s paintings in the 17th century, but never before in Italian Renaissance paintings. Regarding this, Gonzalez commented:

“It tells us also that those recipes were passed on for centuries. It was a very good recipe.”

The scientist also stated that there is still a lot to be discovered, and what they are saying is just a scratch on the surface of many other such mysteries hidden in the painting.

Mona Lisa | the Muse for Leonardo da Vinci

Leonardo da Vinci’s Alchemical Ground Layer

Plumbonacrite, containing carbon, hydrogen, lead, and oxygen, is an unstable compound that can only exist in alkaline environments. The scientists concluded that it formed when da Vinci dissolved lead(II) oxide (PbO) powder in his oil medium, likely linseed or walnut oil, and heated it. He used this mixture as the preparatory undercoat of his painting on the poplar panel on which he painted the ‘Mona Lisa’. 

Lead(II) oxide, now known to be a toxic compound, thickened the texture of the ground layer and also possessed faster drying properties. This created a broader, more stable surface ideal for the sfumato technique—the soft, seamless transitions between tone and color that give her expression its radiant ambiguity. 

To put it simply, the honey-like medium was perfect for painting on wood—a stubborn substrate that naturally flexes and cracks over time.  Moreover, plumbonacrite also imparts a pearlescent effect to the surface on which it is used. 

Scientists also discovered plumbonacrite in another of da Vinci’s Renaissance masterpieces, ‘The Last Supper’, after analyzing 17 microsamples that they took from the surface of the mural. The use of lead-based compounds was not a one-off experiment for da Vinci, since he used it again in the ‘Mona Lisa’ after the creation of the biblical mural.

Leonardo da Vinci | Blending Chemistry and History together

Leonardo da Vinci’s Painting Technique Might Have Influenced Rembrandt van Rijn

Dutch artist Rembrandt van Rijn is widely known for using the art of chiaroscuro, the interplay of light and dark in his paintings, which ranged from portraits to landscapes, and even historical and mythological scenes. He is also widely known for his impasto technique, in which diluted paint is applied on the canvas in such a way that it stands out from the surface. 

In 2019, a team of French and Dutch scientists used high-resolution X-ray diffraction spectroscopy to investigate microsamples from four Rembrandt paintings. The study revealed that the impasto applied on the canvas of these paintings contained traces of plumbonacrite. This compound has been a staple pigment since the early 20th century, and is used in industries for the production of  "Modern Lead White" pigment. 

However, before plumbonacrite was discovered in Leonardo da Vinci’s ‘Mona Lisa’ and ‘The Last Supper’, it was believed to have been only used in one pre-20th-century painting, Vincent Van Gogh’s ‘Haystack in Rainy Day’. The study conducted in 2023 on his paintings is proof that da Vinci’s painting technique might have influenced artists like Rembrandt to use lead oxide in their paintings. 

Conservation and Legacy of the ‘Mona Lisa’

The Painting of Mona Lisa being Cleaned!

While this discovery incites artistic and historical intrigue, it also necessitates adjustments to art restoration strategies. Plumbonacrite, being an unstable compound, makes the ‘Mona Lisa’ even more sensitive to environmental changes such as humidity, temperature fluctuations, and even the air’s composition. More careful cleaning, retouching, or preservation techniques must be adopted to avoid the breakdown of the lead compound or the painting’s discoloration over time. 

The painting’s survival over five centuries despite the presence of this unstable compound on the canvas stands as a testament to its durability. The controlled environment in the Louvre Museum and centuries of careful handling have also aided its preservation. Thanks to new scientific data about the chemical composition at the molecular level, conservators can now monitor degradation risks more precisely and anticipate long-term preservation needs.

Further, the presence of plumbonacrite also gives insight into Leonardo da Vinci’s creative process, establishing the legacy of ‘Mona Lisa’ as one of the most intriguing pieces in the history of art. Each discovery changes how the present and future generations of artists study this painting. 

It also inspires new artists to try a more interdisciplinary approach by blending their knowledge of chemistry and history, just like da Vinci, who carefully engineered his materials to achieve visual effects that were both subtle and structurally sound.