Joe McConnell
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“Old Masters” such as Leonardo da Vinci, Sandro According to Botticelli and Rembrandt they may have used proteins, particularly egg yolk, in their oil paintings a new study.
Traces of protein residues have long been detected in classic oil paintings, though they were often 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 paints.
“There are very few written sources on this and no scientific work has ever been done to investigate this topic 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 telephone interview. “Our results show that even with a very small amount of egg yolk, you can achieve a surprising change in properties in oil paint, demonstrating how it could have been useful to artists.”
Apparently, simply adding a little egg yolk to their works could have lasting effects that went beyond mere aesthetics.
Compared to the means 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 more slowly, 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 disadvantages, including being more susceptible to color darkening and damage from exposure to light.
Because paint production 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, researchers recreated the paint-making process using four ingredients (egg yolk, distilled water, linseed oil, and pigment) to mix two historically popular and significant colors, lead white and ultramarine.
“The addition of egg yolk is beneficial because it can change the properties of these paints dramatically,” Ranquet said, “for example by showing aging differently: it takes longer for the paint to oxidize, because of the antioxidants in the yolk.”
Chemical reactions between the oil, pigment and proteins in the yolk directly influence the behavior and viscosity of the paint. “For example, lead white pigment is quite sensitive to moisture, but if you coat it with a layer of protein, it becomes much more resistant, making the paint quite easy to apply,” Ranquet said.
“On the other hand, if you want something more rigid without having to add a lot of pigment, with a little egg yolk you can create a high impasto paint,” he added, referring to a painting technique in which paint is applied in a brushstroke thick enough that the brush strokes are still visible. Using less pigment would have been desirable centuries ago, when some pigments, such as lapis lazuli, which was used to create ultramarine, were more expensive than gold, according to Ranquet.
Direct evidence of the effect of egg yolk in oil painting, or its absence, can be seen in Leonardo da Vinci’s “Madonna of the Carnation”, one of the paintings observed during the study. Currently exhibited at the Alte Pinakothek in Munich, Germany, the work shows evident wrinkles on the faces of Mary and the child.
“Oil paint starts to dry from the surface down, and that’s why it wrinkles,” Ranquet said.
One of the causes of wrinkles could be an insufficient amount of pigment in the paint and the study showed that this effect could be avoided by adding egg yolk: “It’s quite surprising because you have the same amount of pigment in the paint, but the presence of egg yolk changes everything.”
Since wrinkles form within a few days, it is likely that Leonardo and others The old masters may have captured this particular effect, as well as the 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 newly popular medium of oil painting.
New understanding of the classics
Another painting observed during the study was Botticelli’s “The Lamentation over the Dead Christ”, also exhibited at the Alte Pinakothek. The work is made mainly with tempera, but oil paint was used for the background and some secondary elements.
“We knew that some parts of the paintings show brush strokes typical of what we call oil paint, and yet we detected the presence of proteins,” Ranquet said. “Since it’s a very small amount and they’re difficult to detect, this could be dismissed as contamination. In the workshops, the artists used a lot of different things, and perhaps the eggs were just from the tempera.”
However, since the addition egg yolk had such desirable effects on oil paint, the presence of protein in the work could be an indication of deliberate use, instead, the study suggested. Ranquet hopes that these preliminary findings will draw more curiosity to 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, agrees. “This exciting paper provides a new framework for understanding ancient painting techniques,” she said in an email.
“The research team, reporting results from the molecular level to the macroscopic scale, contributes to a new understanding of the use of egg yolk and oil binders. They no longer limit themselves to simply identifying the materials used by the ancient masters, but explain how they could produce wonderful and sparkling effects by using and mixing the few natural materials available. They try to uncover the secrets of old recipes about which little or nothing is written,” he added.
“This new knowledge contributes not only to better conservation and preservation of works of art, but also to a better understanding of the history of art.”
Top Image: Leonardo Da Vinci’s “Mona Lisa”
