The secret of the ‘Mona Lisa’, a surprising mixture of toxic pigments

Leonardo da Vinci He is known to this day for his innovations in the arts and sciences, including his famous kitchen notes, which began with strict cleaning of the work area.

Now, new analyzes published in the Journal of the American Chemical Society show that his taste for experimentation extended to the basic layers beneath his paintings. Surprisingly, samples of the Mona Lisa And The last Supper suggest that he experimented with lead oxide, creating among his works of art a rare compound called plumbonacrite, with a high lead content and an appearance similar to that of pearls.

The paints and pigments in Da Vinci’s studio have always been the subject of scientific research. The Mona Lisalike many other paintings of the early 16th century, work was done on wooden panels prepared with a thick layer of base paint that had to be allowed to harden before starting the pigments.

But While other artists used gesso (a mixture of binder with chalk, plaster or pigment), Leonardo experimented with applying thick layers of white lead, a synthetic mineral pigment that has been used since ancient times. He also mixed his oil paint with lead oxide, an orange pigment that gave very specific drying properties to the final layer of paint.

He used a similar technique on the wall below The last Supper, unlike the traditional fresco used at the time.

To better investigate this, Víctor González, leader of the research team, wanted to apply high-resolution techniques to small samples of the two paintings. The team conducted their analyzes on a microsample previously obtained from a corner of the Earth Mona Lisaas well as 17 microsamples from the surface of The last Supper.

They determined this using X-ray and infrared techniques The base layers contain not only oil and white lead, but also a much rarer compound: plumbonacrite. (Pb5(CO3)O(OH)2). This material has not previously been found in paintings from the Italian Renaissance, although it is present in Rembrandt’s later works from the 17th century.

Plumbonacrite is only stable under alkaline conditions, indicating that it was formed from a reaction between oil and lead oxide. Most samples of the Last Supper contained intact grains of this latter material.

Painters are known to have added lead oxides to pigments to help them dry, but the technique had not previously been found in paintings from Da Vinci’s time. In fact, There was evidence of this powerful poison only in writings on remedies for skin and hair. They helped Leonardo create the works of art we know today. (JO)