Leonardo Da Vici, Sandro Botticelli or Rembrandt were just some of the painters who added eggs to their oil paintings. It is evident that it was not an impromptu decision. Some objective was pursued by the development of this pictorial technique that today is known as tempera painting.
Researchers at the Karlsruhe Institute of Technology have discovered that using the yolk can overcome moisture problems, wrinkles on the surface and yellowing, as they explain in an article published in the journal Nature Communications.
Scientists say that these findings may help in the conservation and preservation of the works of art of some old masters of the Italian Renaissance. Because when egg proteins form a thin shell around pigment (color) particles, they suppress water absorption from humid environments.
Adding the yolk provides rigid paints with a strong impasto (texture) and prevents surface wrinkling during drying. Antioxidants also help prevent yellowing by slowing down the reaction between oxygen and oil components on drying to reduce the formation of a solid film.
Tempera painting has a long historical tradition, appearing in works such as those found in the Palace of Nestor in Pylos (Greece) dating from 1200 BC. In the 15th century, however, there was a shift in Europe towards using oil as a binder, an approach favored by early Dutch painters such as Jan van Eyck.
Despite the change, eggs have continued to be found in the works of Old Masters such as Sandro Botticelli and Leonardo da Vinci. "The egg is used to modify and adjust the properties of the paint," says Dr. Patrick Dietemann, one of the study's authors.
The researchers created three types of paint. The first was made from pigment ground with linseed oil, the second used the same mixture but with the addition of a few drops of egg yolk, and the third was created by mixing a pigment with a diluted egg yolk solution. After drying, it was ground and dispersed with oil.
“By changing the preparation technique, the properties of the paint vary. Therefore, two paints with the same composition can have different microstructures and this will result in different properties”, adds Dr. Ilaria Bonaduce. The yolk, for example, protects paints from changes caused by the absorption of humidity from the environment, because the water remains attached to the protein layer.
