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“Old Masters” like Leonardo da Vinci, Sandro Botticelli, and Rembrandt might have incorporated proteins, particularly egg yolk, in their oil paintings, based on a recent study.
Minute traces of protein residue have historically been found in classic oil paintings, although they were typically attributed to contamination. A newly published study in the journal Nature Communications suggests the addition was likely intentional — providing insights into the technical expertise of the Old Masters, the most accomplished European painters of the 16th, 17th, or early 18th century, as well as their paint preparation methods.
“There are very few documented sources on this, and no prior scientific research has delved into the topic as thoroughly,” explained study author Ophélie Ranquet of the Institute of Mechanical Process Engineering and Mechanics at the Karlsruhe Institute of Technology in Germany, via phone. “Our findings indicate that even a minuscule amount of egg yolk can cause significant changes in the properties of oil paint, highlighting its potential benefits for artists.”
The simple act of integrating egg yolk into their creations, it appears, could have enduring effects that extend beyond mere aesthetics.
Eggs versus oil
In contrast to the medium used by ancient Egyptians known as tempera — which mixes egg yolk with ground pigments and water — oil paint produces more vibrant colors, facilitates smoother color transitions, and dries significantly slower, allowing for several days of use post-mixing. Nevertheless, oil paint, which utilizes linseed or safflower oil instead of water, also has its downsides, including greater susceptibility to color darkening and degradation from light exposure.
Given that paint production was a craft and an experimental endeavor, it is possible that the Old Masters incorporated egg yolk, a familiar substance, into this newer form of paint, which first emerged in the seventh century in Central Asia before spreading to Northern Europe during the Middle Ages and to Italy in the Renaissance. The researchers in the study replicated the paint-making process using four constituents — egg yolk, distilled water, linseed oil, and pigment — to create two historically significant colors, lead white and ultramarine blue.
“The incorporation of egg yolk is advantageous as it dramatically adjusts the properties of these paints,” remarked Ranquet, “For instance, it influences how the paint ages: the oxidation process takes longer due to the antioxidants found in the yolk.”
The chemical interactions between the oil, the pigment, and the proteins in the yolk directly impact the paint’s characteristics and viscosity. “For example, the lead white pigment is considerably affected by moisture, but if coated with a protein layer, it becomes much more resilient, allowing for easier application of the paint,” explained Ranquet.
“Conversely, if a stiffer texture is desired without an excess of pigment, a small addition of egg yolk will yield a high impasto paint,” she elaborated, referencing a technique where paint is applied in such a way that the brushstrokes remain visible. Using less pigment would have been advantageous centuries ago when certain pigments — like lapis lazuli, utilized for ultramarine blue — were valued more than gold, according to Ranquet.
Clear evidence regarding the influence of egg yolk in oil paint, or its absence, can be examined in Leonardo da Vinci’s “Madonna of the Carnation,” one of the artworks studied. Currently located at the Alte Pinakothek in Munich, Germany, this piece exhibits noticeable wrinkling on the face of Mary and the child.
“Oil paint dries from the top layer down, which is the reason it wrinkles,” Ranquet stated.
One potential cause of wrinkling might be a deficiency of pigments in the mixture, and the study demonstrated that the introduction of egg yolk can mitigate this effect: “That’s rather extraordinary because the pigment quantity remains unchanged in your paint, yet the presence of egg yolk alters everything.”
Since wrinkling can occur within a few days, it’s plausible that Leonardo and other Old Masters may have recognized this specific effect, in addition to the other advantageous features of egg yolk in oil paint, such as humidity resistance. The “Madonna of Carnation” is among Leonardo’s earlier works, created during a period when he may still have been mastering the then-nascent medium of oil paint.
Fresh insights into classical art
Another artwork examined in the study was “The Lamentation Over the Dead Christ,” by Botticelli, also showcased at the Alte Pinakothek. This piece predominantly utilizes tempera, with oil paint applied for the background and some additional elements.
“We were aware that certain sections of the paintings displayed brushstrokes typical of what we refer to as oil painting, yet we identified proteins’ presence,” Ranquet noted. “Due to their minimal quantity and difficulty in detection, this might be dismissed as mere contamination: In studios, artists utilized a multitude of materials, and perhaps the eggs were simply from the tempera.”
However, considering the positive effects of incorporating egg yolk into oil paint, the presence of proteins in the artwork may suggest intentional use instead, the study proposed. Ranquet aspires that these initial findings may spark greater interest in this underexplored field.
Maria Perla Colombini, a professor of analytical chemistry at the University of Pisa in Italy, who did not participate in the study, concurred. “This stimulating paper establishes a new perspective for understanding ancient painting methods,” she mentioned in an email.
“The research team, relaying findings from the molecular level to a macroscopic scale, enhances our comprehension of the use of egg yolk and oil binders. They aim not only to identify the materials utilized by the Old Masters but to elucidate how they achieved magnificent and shimmering effects using a limited selection of natural resources. They seek to unveil the secrets of ancient recipes, about which little or nothing has been documented,” she elaborated.
“This newfound knowledge will not only enhance the conservation and preservation of artworks but also lead to a richer understanding of art history.”
Top image: The “Mona Lisa” by Leonardo Da Vinci
