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New research suggests that “old masters” such as Leonardo da Vinci, Sandro Botticelli and Rembrandt, and in particular oil paintings, proteins, especially egg yolks, may have been used.
Trace protein residues have long been detected in classical oil paintings, but often result from contamination. A new study published Tuesday in Nature Communications found that inclusion was likely intentional. It sheds light on the technical knowledge and how the paint is prepared by the old masters, the most skilled European painters of the 16th, 17th, or early 18th centuries.
“There is very little written source of information on this. No scientific research has been conducted to investigate the subject at this depth,” said Ophélie Ranquet, a research author at the Institute of Mechanical Process Engineering and Mechanical Engineering at the Karlsruhe University of Technology in Germany, in a telephone interview. “Our results show that even with very small amounts of egg yolks can achieve an incredible change in the properties of oil paint, and demonstrate how this is beneficial to artists.”
Simply adding egg yolk to their work reveals that it can have long-term effects that go beyond mere aesthetics.
Compared to the medium formulated by the ancient Egyptians called Temea, which combines egg yolk, powdered pigment and water, oil paint produces stronger colors, allowing for very smooth color transitions and dry much faster, allowing for use for several days after preparation. However, oil paints that use flaxseed or safflower oil instead of water are prone to darkening in color and have drawbacks such as damage from exposure to light.
Since making paint was an craftsman and experimental process, the old masters may have added the familiar material, egg yolk, to the new types of paint. In this study, the researchers replicated the painting process by mixing two historically popular colours with the white and ultramarine blues into lead, using four components: egg yolk, distilled water, linseed oil and pigments.
“The addition of egg yolk is beneficial because it allows you to dramatically adjust the properties of these paints,” Lankett said. “By showing aging differently: it takes longer for the paint to oxidize due to the antioxidants found in egg yolk.”
The chemical reaction between egg yolk oils, pigments and proteins directly affects the behavior and viscosity of the paint. “Lead white pigments, for example, are very sensitive to humidity, but when coated with a protein layer, they make them much more resistant and make the paint very easy to apply,” says Ranquet.
“On the other hand, if you want something to be hard without adding a lot of pigments, using a little egg yolk can create a high impact paint,” she added. According to Lanket, certain pigments, such as lapis lazuli, which were used to make ultramarine blue, were sometimes more expensive than gold, according to the Lanket.
Direct evidence, or lack of the effect of egg yolk in oil painting, can be seen in Leonardo da Vinci's “Madonna of Carnation,” one of the paintings observed during the study. Currently on display at Alte Pinakothek in Munich, Germany, the work shows the obvious wrinkles on the faces of Mary and her child.
“The oil paint starts to dry out from the surface, so it's wrinkled,” Lanket said.
One reason for wrinkles is that the amount of body shape in the paint may be insufficient, and this study shows that adding egg yolks can avoid this effect.
As wrinkles occur within a few days, it is possible that Leonardo and other old masters have been caught up in this particular effect and the beneficial properties of egg yolks in oil paints, including resistance to humidity. “Madonna of Carnation” was one of Leonardo's earliest paintings and was created when he might have been trying to master the new and popular oil paints.
A new understanding of classics
Another painting observed during the study was “Lament to the Dead Christ” and was also on display in Arte Pinakotec. The work is primarily made with tempera, but oil paint is used for the background and some secondary elements.
“I knew that some of the paintings exhibit brush strokes typical of what is called oil paintings, but we detected the presence of protein,” Lankett said. “It's a very small amount and difficult to detect, so this could be dismissed as a contamination. In the workshop, the artists used many different things and the eggs were from the tempera.”
However, as the addition of egg yolks has a highly desirable effect on oiling, the presence of proteins in studies could instead be a sign of intentional use, studies suggest. Lanket hopes that these preliminary findings may attract more curiosity towards this unstudied topic.
Maria Perla Columbini, a professor of analytical chemistry at the University of Pisa in Italy, agreed that she was not involved in the study. “This exciting paper provides a new scenario for understanding old painting techniques,” she said in an email.
“The research group reports molecular level results up to a macroscopic scale, contributing new knowledge about the use of egg yolks and oil binders. They are not merely looking at identifying the materials used by older masters, but explaining how to create a great effect by adopting and mixing several available natural materials.
“This new knowledge contributes not only to better conservation and preservation of artwork, but also to a better understanding of art history.”
Top image: “Mona Lisa” by Leonardo Da Vinci