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Scientists identify secret ingredient in Leonardo da Vinci paintings

“Old Masters” such as leonardo da Vinci, Sandro Botticelli and Rembrandt may have used proteins, especially egg yolk, in their oil paintings, according to a new study.

Trace quantities of protein residue have long been detected in classic oil paintings, though they were often ascribed to contamination. A new study published on Tuesday in the journal Nature Communications found the inclusion was likely intentional — and sheds light on the technical knowledge of the Old Masters, the most skilled European painters of the 16th, 17th, or early 18th century, and the way they prepared their paints.

“There are very few written sources about this and no scientific work has been done before to investigate the subject in such depth,” said study author Ophélie Ranquet of the Institute of Mechanical Process Engineering and Mechanics at the Karlsruhe Institute of Technology in Germany, in a phone interview. “Our results show that even with a very small amount of egg yolk, you can achieve an amazing change of properties in the oil paint, demonstrating how it might have been beneficial for the artists.”

Simply adding some egg yolk to their works, it turns out, could have long-lasting effects that went beyond just aesthetics.

Eggs vs oil

Compared with the medium formulated by ancient Egyptians called tempera — which combines egg yolk with powdered pigments and water — oil paint creates more intense colours, allows for very smooth colour transitions and dries far less quickly, so it can be used for several days after its preparation. However, oil paint, which uses linseed or safflower oil instead of water, also has drawbacks, including being more susceptible to colour darkening and damage caused by exposure to light.

Because making paint was an artisanal and experimental process, it is possible that the Old Masters might have added egg yolk, a familiar ingredient, to the newer type of paint, which first showed up in the seventh century in Central Asia before spreading to Northern Europein the Middle Ages and Italy during the Renaissance.

In the study, the researchers recreated the process of paint-making by using four ingredients — egg yolk, distilled water, linseed oil and pigment — to mix two historically popular and significant colours, lead white and ultra marine blue.

The chemical reactions between the oil, the pigment and the proteins in the yolk directly affect the paint’s behaviour and viscosity. A direct evidence of the effect of egg yolk in oil paint, or lack thereof, can be seen in leonardo da Vinci’s Madonna of the Carnation, one of the paintings observed during the study. Currently on display at the

Alte Pinakothek in Munich, Germany, the work shows evident wrinkling on the face of Mary and the child.

“Oil paint starts to dry from the surface down, which is why it wrinkles,” Ranquet said.

One reason for wrinkling may be an insufficient quantity of pigments in the paint, and the study has shown that this effect could be avoided with the addition of egg yolk.

Because wrinkling occurs within days, it’s likely that leonardo and other Old Masters might have caught onto this particular effect, as well as additional beneficial properties of egg yolk in oil paint, including resistance to humidity.

The Madonna of Carnation is one of leonardo’s earliest paintings, created at a time when he might have been still trying to master the then newly popular medium of oil paint.

New understanding of the classics

Another painting observed during the study was The Lamentation Over the Dead Christ, by Botticelli, also on display at the Alte Pinakothek.

The work is mostly made with tempera, but oil paint has been used for the background and some secondary elements. However, because adding egg yolk had such desirable effects on oil paint, the presence of proteins in the work might be an indication of deliberate use instead, the study suggested. Ranquet hopes that these preliminary findings might attract more curiosity toward this understudied topic.

Maria Perla Colombini, a professor of analytical chemistry at the University of Pisa in Italy, who was not involved in the study, agreed.

“This exciting paper provides a new scenario for the understanding of old painting techniques,” she said in an email. “The research group, reporting results from molecular level up to a macroscopic scale, contributes to a new knowledge in the use of egg yolk and oil binders.

“This new knowledge contributes not only to a better conservation and preservation of artworks, but also to a better comprehension of art history.” — CNN.

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2023-03-31T07:00:00.0000000Z

2023-03-31T07:00:00.0000000Z

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