Old Master’s secret ingredient? Egg yolk, a new study suggests
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“Old Masters” such as Leonardo da Vinci, Sandro Both Botticelli and Rembrandt probably used proteins, especially egg yolk, in their oil paintings, respectively a new study.
Traces of residual protein have long been found in classic oil paintings, although they were often referred to as 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 the way they prepared their paint.
“There are very few written sources about this and no scientific work has been done before to study the subject in such depth,” said study author Ophélie Ranquet from 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 small amount of egg yolk, you can make a dramatic change to the properties in the oil paint, showing how it could be beneficial for artists.”
By adding a little egg yolk to their works, it turns out that it could have lasting effects that went beyond mere beauty.
Compared to the medium created by the so-called ancient Egyptians tempera – which combines egg yolk with powdered pigments and water – oil paint creates more intense colors, allows very smooth color transitions and dries much faster, so it can be used for several days after its preparation. However, oil paints, which use linseed or safflower oil instead of water, have disadvantages, including being more prone to color darkening and damage caused by exposure to light.
Since making paint was an artisanal and experimental process, the Old Masters may have added egg yolk, a familiar ingredient, to the latest type of paint, which first appeared in the seventh century in Central Asia before spreading to Northern Europe in the Middle Ages and Italy during the Renaissance. In the study, the researchers recreated the paint-making process by using four ingredients – egg yolk, distilled water, cooking oil and dye – to mix two historically popular colors, lead white and ultramarine blue.
“Adding egg yolk is beneficial because it can fine-tune the properties of these paints in a dramatic way,” said Ranquet, “For example by showing age in a different way: it takes longer for the paint to oxidize, due to the antioxidants in the dye.”
The chemical reactions between the oil, the dye and the proteins in the yolk directly affect the behavior and viscosity of the paint. “For example, the main color white is very sensitive to moisture, but if you cover it with a protein layer, it will be much more resistant to it, making the paint very easy to apply,” said Ranquet.
“On the other hand, if you wanted something harder without having to add a lot of color, with a little egg yolk you can create a high impasto paint,” she said, referring to a painting technique where the paint is applied in a stroke thick enough that the brushstrokes are still visible. Using less color would have been desirable centuries ago, when certain pigments – such as lapis lazuli, used to make ultramarine blue – more expensive than gold, according to Ranquet.
Direct evidence of the effect of egg yolk on oil paint, or lack thereof, can be seen in Leonardo da Vinci’s “Madonna of the Carnation”. one of the pictures seen during the investigation. Currently on display at the Alte Pinakothek in Munich, Germany, the work shows a prominent frown on the face of Mary and the child.
“Oil paint begins to dry from the surface down, which is why it wrinkles,” said Ranquet.
One reason for wrinkling may be the amount of color in the paint, and the study showed that this effect could be avoided by adding egg yolk: “That’s quite surprising because you have the same amount of color in your paint, but the presence of egg yolk changes everything.”
Since wrinkling occurs within days, it seems that Leonardo and others Old Masters may have seized on this particular effect, as well as the additional beneficial properties of egg yolk in oil paint, including resistance to moisture. The “Madonna of Carnation” is one of Leonardo’s earliest paintings, created at a time when he may still be trying to master the oil paint medium that was popular at the time.
Another painting seen during the survey was “The Lamentation Over the Dead Christ,” by Botticelli, also on display at the Alte Pinakothek. Most of the work is done in tempera, but oil paint was used for the background and some of the secondary elements.
“We knew that some of the paintings show brushstrokes that are typical of what we call oil painting, but nevertheless we found the presence of proteins,” said Ranquet. “Since it is a very small number and they are difficult to find, this could be dismissed as contamination: In workshops, artists used many different things, and the eggs were probably just from the tempera.”
However, because ‘put egg yolk had such a desirable effect on oil paint, the presence of proteins in the work could indicate a deliberate use, instead, the study suggested. Ranquet hopes that these preliminary findings may draw more curiosity towards this under-researched topic.
Maria Perla Colombini, a professor of analytical chemistry at the University of Pisa in Italy, who was not involved in the study, agreed. “This fascinating paper provides a new setting for understanding ancient painting techniques,” she said in an email.
“The research group, reporting results from the molecular level up to the macroscopic scale, contributes to new knowledge on the use of egg yolk and oil binders. They are no longer looking at just identifying the materials used by the Old Masters but explaining how they could produce a wonderful and shiny effect by using and mixing the few natural materials available. They try to discover the secrets of old recipes on which little or nothing is written,” she said.
“This new knowledge contributes not only to better conservation and preservation of works of art but also to a better understanding of art history.”
Image above: The “Mona Lisa” by Leonardo Da Vinci