An Old Master’s secret ingredient? Egg yolk, new study suggests

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The “old masters” like Leonardo da Vinci, Sand Botticelli and Rembrandt may have used proteins, in particular egg yolk, in their oil paintings, according to a new study.

Traces of quantities of protein residues have long been detected in conventional oil paintings, although they have often been attributed to contamination. A New study published Tuesday in the newspaper Nature communications revealed that inclusion was probably intentional – and highlights the technical knowledge of the former masters, the most qualified European painters of the 16th, 17th or early 18th century, and in the way in which they prepared their paintings.

“There are very few written sources on this subject and no scientific work has been done before to study the subject in depth,” said the study author, Ophélie Ranquet of the Mechanical Process and Mechanical Institute of the Karlsruhe Institute of Technology in Germany, in a telephone interview. “Our results show that even with a very small amount of egg yolk, you can make an incredible change in properties in oil painting, demonstrating how it could have been beneficial for artists.”

It turns out that adding an egg yolk to their works could have lasting effects that went beyond aesthetics.

Compared to the environment formulated by the ancient Egyptians called Tempera – which combines egg yolk with powdered pigments and water – oil paint creates more intense colors, allows very smooth and dried color transitions much less quickly, so it can be used for several days after its preparation. However, oil paint, which uses lin or cartame oil instead of water, also has drawbacks, including being more likely to darken colors and damage caused by exposure to light.

Because the manufacture of painting was an artisanal and experimental process, it is possible that the ancient masters added the egg yolk, a familiar ingredient, to the new type of painting, which appeared for the first time in the 7th century in Central Asia before Distribution in Northern Europe In the Middle Ages and Italy during the Renaissance. In the study, the researchers recreated the paint manufacturing process using four ingredients – egg yolk, distilled water, linseed oil and pigment – to mix two historically popular and significant colors, lead white and ultramarine blue.

“The addition of egg yolk is beneficial because it can adjust the properties of these paintings in a drastic way,” said Ranquet, “for example by showing differently aging: it takes more time to paint to oxidize, due to the antioxidants contained in yellow.”

The chemical reactions between oil, pigment and yellow proteins directly affect the behavior and viscosity of the paint. “For example, the white lead pigment is quite sensitive to humidity, but if you cover it with a layer of protein, this makes it much more resistant, which makes paint fairly easy to apply,” said Ranquet.

“On the other hand, if you wanted something more rigid without having to add a lot of pigment, with a little egg yolk, you can create a strong implasto paint,” she added, referring to a paint technique where the paint is arranged in a line thick enough for the brush strokes to always be visible. The use of fewer pigments would have been desirable centuries ago, when some pigments – such as Lapis Lazuli, which was used to make ultramarine blue – were more expensive than gold, according to Ranquet.

Direct proof of the effect of egg yolk in oil painting, or its absence, can be observed in the “Madonna of the Carnation” by Leonardo da Vinci, “ One of the paintings observed during the study. Currently exhibited at the Alte Pinakothek in Munich, Germany, work shows obvious offensions on the face of Mary and the child.

“Oil painting begins to dry from the surface below, which is why it wrinkles,” said Ranquet.

One of the reasons for the wrinkle can be an insufficient quantity of pigments in painting, and the study has shown that this effect could be avoided with the addition of egg yolk: “It is quite surprising because you have the same quantity of pigment in your painting, but the presence of egg yolk changes everything.”

Because wrinkles occur in a few days, it is likely that Leonardo and others Ancient masters may have taken this particular effect, as well as additional beneficial properties of egg yolk in oil paint, including humidity resistance. The “Madonna of Carnation” is one of Leonardo’s first paintings, created at a time when it could always have controlled the newly popular oil painting.

New understanding of classics

Another painting observed during the study was “lamentation on dead Christ”, by Botticelli, also exposed to the Alte Pinakothek. The work is mainly done with temperatures, but oil paint was used for the background and certain secondary elements.

“We knew that certain parts of the paintings show brush strokes typical of what we call an oil painting, and yet we have detected the presence of proteins,” said Ranquet. “Because it is a very small quantity and they are difficult to detect, it could be rejected as a contamination: in the workshops, the artists used a lot of different things, and perhaps the eggs came from the temperature.”

However, because the addition The egg yolk has had such desirable effects on oil painting, the presence of proteins in the work could be an indication of deliberate use instead, The study suggested. Ranquet hopes that these preliminary results could attract more curiosity to this sub-studied subject.

Maria Perla Colombini, professor of analytical chemistry at the University of Pisa in Italy, which was not involved in the study, agreed. “This exciting article provides a new scenario to understand the old painting techniques,” she said in an email.

“The research group, signaling the results of the molecular level to a macroscopic scale, contributes to a new knowledge in the use of laces of egg yolks and oil. They do not seek more to simply identify the materials used by the old masters, but to explain how they could produce wonderful and sparkling effects by using and mixing the few natural materials available.

“This new knowledge contributes not only to a better conservation and preservation of works of art, but also to a better understanding of the history of art.”

Image of the Top: The “Mona Lisa” of Leonardo da Vinci