'Eggcellent work': Scientists gain insights into old master artists' use of egg in oil paintings

Whether they're poached, scrambled or fried, everyone has their favorite way of preparing eggs. But some of the world's most famous artists made use of them in a different manner – by adding them to paint, a study suggests.

The likes of Sandro Botticelli and Leonardo da Vinci, also known as 'Old Master' artists, may have added protein to their oil paintings to overcome issues with humidity, surface wrinkling and yellowing, researchers have discovered.

The use of egg as a binding medium for pigments, a form of paint known as egg tempera, has a long history, turning up in works including the mural paintings of the Palace of Nestor in Pylos, dating to 1200BC.

A team led by scientists at the Karlsruhe Institute of Technology in Germany examined the effects of adding protein in the form of egg yolk to oil paints. Writing in the journal Nature Communications, the research team report how they explored the issue by creating three types of paint.

"[The] egg is used for modification and fine-tuning of paint properties," said Dr Patrick Dietemann, who joined in the research from the Doerner Institut in Germany.

The team discovered water uptake from humid environments can be suppressed when the egg proteins formed a thin layer around the particles of paint pigment. Adding egg yolk was also found to provide stiff paints with strong impasto - being able to layer it on thickly - and prevented wrinkling of the surface during drying.

The study reveals egg yolk generally increased the drying time of paints, a feature the researchers attributed to its antioxidant properties, which also help to protect the paints from degrading over time. Antioxidants within the yolk also helped prevent the paint from yellowing when it dried, by slowing the reaction between oxygen and oil.

Prof Norbert Willenbacher, an author of the study from the Karlsruhe Institute of Technology, said "[The yolk] protects the paints from undesirable changes caused by absorption of moisture from the environment, because the water is captured in the protein layer [surrounding the pigments]."

The researchers explained the founding in journal article: "The technical knowledge of the Old Masters, how paints had to be prepared, was initially passed down in workshops but is lost today. We investigated oil paints with a small amount of added egg yolk to better understand Old Masters' paintings and their techniques."

While the team said it was not possible to exclude unintentional additions of egg to the oil paints, Dr Ilaria Bonaduce, an author of the study from the University of Pisa, said it was likely the Old Master artists were well aware of the benefits of the ingredient. "I am quite convinced that they did not know the chemical and physical explanations of what they were doing, but they knew very well what they were doing."