Art historians have known for some time that Old Masters such as Leonardo da Vinci and Sandro Botticelli mixed egg yolks into their oil paints. Now, scientists may have discovered the reason why. An article published last Tuesday in the journal Nature Communications suggests that these Renaissance painters may have known about egg yolk’s ability to protect their works against damage.
Scientists incorporated egg yolk into oil paint for their experiment using two methods: first, by directly mixing yolk and oil paint with a palette knife, creating a thick and stiff consistency; then, by grinding pigment with drops of diluted yolk and then mixing in oil, a technique Renaissance painters may have employed. For both samples, the presence of egg yolk slowed yellowing of the paint.
Ophélie Ranquiet, the study author and a chemical engineer at the Karlsruhe Institute of Technology in Germany, told CNN that their study is one of few to examine these techniques in depth. Scientists and historians had long assumed the trace amounts of proteins found in paintings were due to contamination between oil and egg tempera. However, Ranquiet and her team now believe the addition was purposeful. She and her team hope their experimental findings encourage further study into these techniques.
During the 15th century, artists such as da Vinci and Botticelli began experimenting with oil painting versus egg tempera. In “The Lamentation Over the Dead Christ” (1490–1492), Botticelli painted Christ, Mary Magdalene, and the Virgin, among others, with tempera, and the background stone and foregrounding grass with oil. This new type of paint looked more vibrant on canvases, blended more seamlessly, and dried slower, allowing artists to work longer on pieces. However, artists using oil would have discovered some kinks, namely wrinkling. Da Vinci possibly struggled in early paintings to use oil as his “Madonna of the Carnation” (1478–1480) features rare and extensive creases around the Virgin’s face. As wrinkling starts to form as the wet paint dries, da Vinci would have learned to mix yolk into oil paints.
Patrick Dietemann, a researcher at Munich’s Doerner Institute who worked on the study, told Hyperallergic that he hopes this work will lead to a better understanding of the chemical composition of Renaissance artworks.
“This hopefully improves our understanding of how beautiful artworks were created and how they degrade on a molecular level, giving insight into how we can protect them better for future generations,” Dietemann said.
Speaking about how these findings might affect art conservators, Vice-President at the American Institute for Conservation (AIC) Dr. Corina Rogge said the new information would help conservators when deciding on treatments as oil and egg require different processes. Questions about how Renaissance painters might have considered their climates when mixing tempera and oil paints or what reactions this method would have with pigments other than ultramarine blue and white immediately arise.
“We’ve probably been underestimating the complexity of these paintings, and while in the past we might have been able to appreciate the artistic skill of the painters, we can now also begin to appreciate their chemical and mechanical skills as well,” Rogge told Hyperallergic.