There was a secret ingredient in Leonardo da Vinci's paintings, reveals new study

"The Renaissance man," Leonardo Da Vinci, and other "old masters" such as Sandro Botticelli made use of proteins, especially egg yolk, in their oil paintings, according to a new study. Trace quantities of protein residue had long been detected in classic oil paintings, though they were often believed to be a result of contamination. A new study published on March 28 in the journal Nature Communications found the inclusion of yolks was likely intentional, reported CNN. The study also sheds light on the technical knowledge of the Old Masters, who were the most gifted European painters of the 16th, 17th, or early 18th centuries, and the way their paints were made. 

"There are very few written sources about this and no scientific work has been done before to investigate the subject in such depth," said study author Ophélie Ranquet of the Institute of Mechanical Process Engineering and Mechanics at the Karlsruhe Institute of Technology in Germany, in a phone interview. "Our results show that even with a very small amount of egg yolk, you can achieve an amazing change of properties in the oil paint, demonstrating how it might have been beneficial for the artists."

Just adding egg yolks to their works could have made long-lasting effects that went beyond just aesthetics.

There is also a debate on egg yolks vs. oil paints. Compared with the paints formulated by ancient Egyptians called "tempera," which combines egg yolk with powdered pigments and water, oil paint creates deeper colors, allows for very smooth color transitions, and dries more quickly. It makes it feasible to use oil paints even several days after their preparation. However, oil paint, which uses linseed or safflower oil instead of water, has its own setbacks, including being more susceptible to color darkening and damage caused by exposure to light.

"The addition of egg yolk is beneficial because it can tune the properties of these paints in a drastic way," Ranquet said, "For example by showing aging differently: It takes a long time for the paint to oxidize, because of the antioxidants contained in the yolk." The chemical reactions between the oil, the pigment, and the proteins in the yolk directly affect the paint's composition. "For example, the lead white pigment is quite sensitive to humidity, but if you coat it with a protein layer, it makes it a lot more resistant to it, making the paint quite easy to apply," Ranquet added.

"On the other hand, if you wanted something stiffer without having to add a lot of pigment, with a bit of egg yolk you can create a high impasto paint," she added, referring to a painting technique where the paint is laid out in a thick enough stroke. Using less pigment would have been desirable centuries ago, as certain pigments — such as lapis lazuli, which was used to make ultramarine blue — were more expensive than gold, reported CNN.

"The research group, reporting results from the molecular level up to a macroscopic scale, contributes to new knowledge in the use of egg yolk and oil binders. They are not looking at simply identifying the materials used by Old Masters but explaining how they could produce wonderful and glittering effects by employing and mixing the few available natural materials. They try to discover the secrets of old recipes of which little or nothing is written,"  Ranquet added. 

This latest discovery will lead to a further analysis of the use of egg yolk in Renaissance paintings and is a surprising revelation!