Materials: Yolk proteins make an eggcellent addition to Old Masters’ oil paintings

‘Old Master’ artists — including Sandro Botticelli, Leonardo da Vinci, and other Italian Renaissance masters — may have added protein to their oil paintings to overcome problems with humidity, surface wrinkling, and yellowing, suggests a Nature Communications paper. The findings improve our understanding of why these artists added protein, such as egg yolk, to their oil paintings and may aid in the conservation and preservation of some Old Master artwork.

Many traditional Old Master artists are known to have used oil as a binding medium in their paints, but proteins have also previously been detected in many of their paintings. However, the reasons why they added protein, and the effects of adding protein to the painting process, are unknown.

Ophélie Ranquet and colleagues examined the effects of adding protein, in the form of egg yolk, to oil paints. They found that water uptake from humid environments, can be suppressed when the egg proteins formed a thin layer around the pigment particles. Adding egg yolk was also found to provide stiff paints with strong impasto and prevented wrinkling of the surface during drying. Antioxidants within egg yolk also helped prevent yellowing when drying by slowing down the reaction between oxygen and oil components to reduce solid film formation.