An old master’s secret ingredient? Egg yolk, suggests a new study

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

Traces of protein residues have long been detected in classical oil paintings, although these have often been attributed to contamination. A new study published Tuesday in the journal Nature Communications found that 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 centuries, and how they prepared their paintings.

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

Simply adding some egg yolks to their works, it turns out, could have long-lasting effects that go beyond just the aesthetic.

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

Because paint-making was an artisanal and experimental process, it is possible that the old masters added egg yolk, a familiar ingredient, to the new type of paint, which first appeared in the 7th century in Central Asia before spreading to Northern Europe in the Middle Ages and Italy during the Renaissance. In the study, the researchers recreated the paint-making process using four ingredients—egg yolk, distilled water, linseed oil, and pigment—to mix two popular and historically significant colors, lead white and ultramarine blue.

“Adding egg yolk is beneficial because it can adjust the properties of these paints in a drastic way,” Ranquet said, “For example, showing aging differently: it takes longer for the paint to oxidize, from because of the antioxidants it contains. in the yolk.”

The chemical reactions between oil, pigment and egg yolk proteins directly affect the behavior and viscosity of the paint. “For example, white lead pigment is quite sensitive to moisture, but if you coat it with a layer of protein, it makes it much more resistant to it, making the paint quite easy to apply,” Ranquet said.

“On the other hand, if you wanted something stiffer without having to add a lot of pigment, with a little egg yolk you can create a large impasto paint,” she added, referring to a painting technique where the paint it is laid down in a stroke thick enough that the brush strokes are still visible. Using less pigment would have been desirable centuries ago, when certain pigments — such as lapis lazuli, which was used to make ultramarine blue — were more expensive than gold, according to Ranquet.

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 Carnations. one of the paintings observed during the study. Currently on display at the Alte Pinakothek in Munich, Germany, the work shows obvious wrinkles 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 can be an insufficient amount of pigments in the paint, and the study showed that this effect could be avoided by adding egg yolk: “It’s quite amazing because you have the same amount of pigment in the paint, but the presence of the yolk of egg changes everything.”

Since the wrinkling appears in a few days, it is likely that Leonardo and others The old masters may have captured this special effect as well as additional beneficial properties of egg yolk in oil paint, including moisture resistance. “Madonna of the Carnation” is one of Leonardo’s earliest paintings, created at a time when he may still have been trying to master the then popular new medium of oil paint.

Another painting observed during the study was Botticelli’s Lamentation over the Dead Christ, also on display at the Alte Pinakothek. The work is mostly done in tempera, but oil paint was used for the background and some secondary elements.

“We knew that some parts of the paintings showed some brushstrokes typical of what we call an oil painting, and yet we detected the presence of proteins,” said Ranquet. “Because it’s a very small amount and they’re hard to detect, this could be dismissed as contamination: in the workshops, the artists used many different things, and maybe the eggs were just tempera.”

However, because the addition egg yolk had such desirable effects on oil paint, the presence of proteins in the work could be an indication of deliberate use, the study suggested. Ranquet hopes these preliminary findings may spark more curiosity about this little-studied 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 work provides a new scenario for understanding ancient painting techniques,” she said in an email.

“The research group, reporting results from the molecular level to a macroscopic scale, contributes new knowledge in the use of egg yolk and oil binders. They no longer aim to identify the materials used by the old masters, but explain how they could produce wonderful and brilliant effects by using and mixing the few natural materials available. They are trying to discover the secrets of old recipes of which little or nothing is written,” she added.

“This new knowledge contributes not only to better preservation and conservation of works of art, but also to a better understanding of art history.”

Top image: “Mona Lisa” by Leonardo Da Vinci

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