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“Old Masters” including Leonardo da Vinci, Sandro Botticelli, and Rembrandt might have incorporated proteins, particularly egg yolk, into their oil paintings, as suggested by a recent study.
Minute traces of protein residue have long been noted in classic oil paintings, although they were often attributed to contamination. A new study revealed on Tuesday in the journal Nature Communications indicated that this inclusion was probably deliberate — providing insight into the technical expertise of the Old Masters, the most accomplished European artists from the 16th, 17th, or early 18th centuries, and the methods they employed in paint preparation.
“There are very few written records on this topic and no prior scientific studies have delved into it so thoroughly,” remarked study author Ophélie Ranquet from the Institute of Mechanical Process Engineering and Mechanics at the Karlsruhe Institute of Technology in Germany, during a telephone interview. “Our findings indicate that even a minimal quantity of egg yolk can bring about a remarkable change in the properties of oil paint, demonstrating its potential advantages for artists.”
Simply introducing some egg yolk into their creations may have had enduring effects that extended beyond mere aesthetics.
Eggs versus oil
In contrast to the medium devised by ancient Egyptians known as tempera — which merges egg yolk with powdered pigments and water — oil paint yields more vivid colors, facilitates smoother color transitions, and dries much slower, permitting its use for several days post-preparation. However, oil paint, utilizing linseed or safflower oil instead of water, possesses disadvantages as well, including increased vulnerability to color darkening and light-induced damage.
Given that paint-making was an artisan and experimental endeavor, it is plausible that the Old Masters introduced egg yolk, a familiar ingredient, into the newer oil paint, which first emerged in the seventh century in Central Asia before spreading to Northern Europe during the Middle Ages and Italy in the Renaissance. The researchers in the study replicated the paint-making process utilizing four ingredients — egg yolk, distilled water, linseed oil, and pigment — to mix two historically important colors, lead white and ultramarine blue.
“Incorporating egg yolk is advantageous as it can significantly alter the characteristics of these paints,” Ranquet stated, “For instance, it affects aging: The oxidation process is prolonged due to the antioxidants found in the yolk.”
The chemical interactions between the oil, the pigment, and the yolk proteins directly influence the paint’s behavior and viscosity. “For example, lead white pigment is notably sensitive to humidity, yet if coated with a protein layer, it becomes significantly more resistant, making the paint considerably easier to apply,” Ranquet explained.
“Conversely, if you desired a stiffer texture without heavily increasing pigment quantity, a small amount of egg yolk could create a high impasto paint,” she noted, referencing a painting technique where the strokes are pronounced enough for the brushwork to remain visible. Using less pigment would have been preferable centuries ago when certain pigments — like lapis lazuli, used for ultramarine blue — were pricier than gold, according to Ranquet.
A clear example of the impact of egg yolk in oil paint, or its absence, can be observed in Leonardo da Vinci’s “Madonna of the Carnation,” one of the artworks examined in the study. Currently exhibited at the Alte Pinakothek in Munich, Germany, this piece reveals noticeable wrinkling on Mary and the child’s faces.
“Oil paint dries from the surface inward, which leads to wrinkling,” Ranquet explained.
One contributing factor to wrinkling may be an inadequate amount of pigments in the paint, and the study has indicated that this could be mitigated with egg yolk: “That’s rather remarkable since you maintain the same pigment quantity in your paint, but the inclusion of egg yolk alters everything.”
Given that wrinkling transpires within days, it’s plausible that Leonardo and other Old Masters recognized this specific effect, along with other advantageous properties of egg yolk in oil paint, such as its resilience to humidity. The “Madonna of Carnation” represents one of Leonardo’s earlier works, created at a time when he might have still been mastering the then popular oil painting technique.
Fresh insights into the classics
A different painting observed during the study was “The Lamentation Over the Dead Christ,” crafted by Botticelli, also exhibited at the Alte Pinakothek. This artwork primarily employs tempera, though oil paint has been utilized in the background and some additional elements.
“We understood that certain sections of the paintings display brushstrokes typical of an oil painting, yet we detected protein presence,” Ranquet remarked. “Noticing such a minimal quantity that may be easily dismissed as contamination is common: Artists often utilized various ingredients in their workshops, and the eggs could have merely been residual from the tempera.”
However, due to the beneficial effects that egg yolk imparts to oil paint, the presence of proteins might suggest its deliberate application instead, the study posited. Ranquet expresses hope that these early findings might inspire more interest in this often-overlooked subject.
Maria Perla Colombini, a professor of analytical chemistry at the University of Pisa in Italy, who did not participate in the study, concurred. “This compelling paper offers a new framework for comprehending old painting methods,” she stated via email.
“The research team, providing insights from molecular to macroscopic dimensions, enhances our understanding of the use of egg yolk and oil binders. They are no longer solely identifying the materials used by Old Masters but elucidating how they could create remarkable and shimmering effects through the utilization and blending of the limited natural materials at their disposal. They aim to unveil the secrets of ancient recipes that are minimally documented,” she continued.
“This newfound knowledge not only aids in the better conservation and preservation of artworks but also enhances our understanding of art history.”
Featured image: The “Mona Lisa” by Leonardo Da Vinci
