Secret Ingredient in Leonardo da Vinci’s Paintings Revealed

Great “old masters” such as Leonardo da Vinci, Sandro Botticelli and Rembrandt may have used proteins, especially egg yolk, in their oil paintings, according to a new study.

Trace amounts of protein residue have long been found in classic oil paintings, although they have often been attributed to contamination. A new study published on 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 how they prepared their paints.

“There are very few written sources about this, and no scientific work has been done on this issue in such depth before,” says study author Ophelie Ranke from the Institute for Mechanical Process Engineering and Mechanics at the Karlsruhe Institute of Technology in Germany. “Our results show that even with a very small amount of egg yolk, an amazing change in the properties of oil paint can be achieved, demonstrating how useful this could be for artists.

As CNN points out, compared to a medium developed by the ancient Egyptians called tempera, which combines egg yolk with powdered pigments and water, oil paint creates more intense colors, produces very smooth color transitions, and dries much faster, so it can be use within a few days of preparation. However, oil paint that uses linseed or safflower oil instead of water also has disadvantages, including being more prone to color fading and light damage.

Because paint making was an artisanal and experimental process, it is possible that the old masters added egg yolk, a familiar ingredient, to a new type of paint that first appeared in the seventh century in Central Asia and then spread to Northern Europe in the Middle Ages and Italy in the Middle Ages. Renaissance. In the study, the researchers recreated the paint-making process using four ingredients – egg yolk, distilled water, linseed oil and pigment – to blend two historically popular and significant colors, lead white and ultramarine blue.

“The addition of egg yolk is beneficial because it can drastically change the properties of these paints,” says Ophelie Ranke, “for example, showing aging in a different way: the paint takes longer to oxidize due to the antioxidants in the yolk.”

The chemical reactions between the oil, pigment and proteins in the yolk directly affect the behavior of the paint and its viscosity. “For example, lead white pigment is quite sensitive to moisture, but if you coat it with a layer of protein, it makes it much more resistant to moisture, which makes the paint quite easy to apply,” says Ranke.

“On the other hand, if you want something a little stiffer, without having to add a lot of pigment, with a little egg yolk you can create a high-density paint,” the study author added, referring to a painting technique in which the paint is applied. a smear thick enough that the smears are still visible. Using less pigment would have been desirable centuries ago, when some pigments, such as lapis lazuli used to make ultramarine blue, were more expensive than gold, Ranke says.

Direct evidence of the effect of egg yolk in oil paint, or its absence, can be seen in Leonardo da Vinci’s Madonna and Carnation, one of the paintings observed during the study. This work is currently on display at the Alte Pinakothek in Munich, Germany. It clearly shows the wrinkles on the face of Mary and the child.

One reason for wrinkling can be the lack of pigments in the paint, and research has shown that this effect can be avoided with the addition of egg yolk: “It’s pretty surprising because your paint has the same amount of pigment, but the presence of egg yolk changes everything.”

Since wrinkling occurs over several days, it is likely that Leonardo and other old masters could have captured this special effect, as well as the additional benefits of egg yolk in oil paint, including moisture resistance. “Madonna with a Carnation” is one of Leonardo’s earliest paintings, done at a time when he may still be trying to master the recently popular oil paint, CNN says.

Another painting seen during the study was Botticelli’s Lamentation over the Dead Christ, also on display in the Alte Pinakothek. The work is mostly done in tempera, but oil paint has been used for the background and some minor elements.

“We knew that some parts of the paintings showed brush strokes typical of what we call an oil painting, and yet we found the presence of proteins,” says Ofeli Ranke.

Because the addition of egg yolk had such a desirable effect on the oil paint, the presence of proteins in the work could be indicative of intentional use, the researchers speculated. Ranke hopes that these preliminary findings may generate more interest in this little-studied topic.