New Study Examines Egg Yolks in Oil Paint

FRIDAY, MARCH 31, 2023


A study published earlier this month reportedly found that the inclusion of proteins such as egg yolk were intentional for the “Old Masters” as they prepared their oil paints. The research was published in the journal Nature Communications.

“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 with CNN.

“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.”

Oil paint can create more intense colors, allow for smooth color transitions and dry far less quickly compared to an older method called tempera, or combining egg yolk with powdered pigments and water.

Because of this, the study found that painters such as Leonardo Davinci, Sandro Botticelli and Rembrandt may have added yolk to the oil paint. For the research, the team reportedly recreated the process of paint-making by using four ingredients—egg yolk, distilled water, linseed oil and pigment—to mix two historically popular and significant colors, lead white and ultramarine blue.

“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 longer time for the paint to oxidize, because of the antioxidants contained in the yolk.”

Additionally, the chemical reactions affect the paint’s behavior and viscosity and make it easier to apply. Researchers have found that it might also prevent a wrinkling effect on works because of the insufficient quantity of pigments in the paint.

Ranquet told reporters that she hopes that these preliminary findings might attract more curiosity toward this understudied topic.

Previous Tempera Research

At the end of 2021, researchers from Sorbonne University in France looked into why tempera paint—also known as egg tempera—was reigned as a supreme medium among Renaissance artists.

According to reports, before oil paints made their debut, the yolk-based paint was utilized for numerous murals in ancient China, Mycenaean Greece, Egypt and Babylonia for its durability, quick-drying properties and the ability to appear opaque and luminous.

To better understand the 15th-century coating’s molecular structure, researchers took to paint recipes recorded in a handbook called Il libro dell'arte by Italian painter Cennino Cennini, according to a French National Center for Scientific Research statement.

As the handbook and additional studies will tell, the yolk-based paint is prepared by mixing colored, powdered pigments with a water-soluble binder (eggs). The result coating is then finished off with a few drops of vinegar to prevent cracking as the paint dries.

However, researchers didn’t stop there. To fully understand the crucial part that the egg yolks play in tempera paint, they created a separate mixture where only water was used as the coating’s binder. For each coating, researchers deployed a clay-based “green earth” (terra verde) pigment, which was widely used as a base layer in Renaissance paintings.

After the paints were properly mixed, researchers brushed the coatings onto a canvas so that they could be analyzed using rheology to measure the paint's flow properties. The researchers also used nuclear magnetic resonance (NMR) relaxometry to measure the physical and chemical properties of the color.

Although the team found that both mixtures' viscosity decreased with shear thinning or stress, the coating that had the most viscosity was the one created with egg yolks. In a statement, the university has suggested that the difference is due to a network of bonds between the egg yolks, water molecules and clay particles in the pigment, making the coating denser than the purely water-based coating.

In September of last year, a team of researchers from global coatings company AkzoNobel discovered several ways of creating the “perfect impasto” as part of a years-long analysis of Rembrandt’s 17th-century masterpiece, “The Night Watch.” Researchers and conservators at the Rijksmuseum in Amsterdam have been working to learn more about the painting for several years as the teams prepare for its first restoration in over 40 years.

AkzoNobel and the Rijksmuseum first announced a partnership and that they’d be working on the 377-year-old painting in July 2019. Previously, "The Night Watch" had been hidden in a bunker within coastal dunes at the start of the second world war. The painting reportedly remained there for four centuries before being rediscovered.

In February 2020, the team released an update on the project, revealing that they had identified three key areas to focus on as the collaboration starts to gather pace.

The “impasto” method, which has also been referred to as wall filler, involves layering paint thickly enough to stand out from the canvas. The team then discovered that the innovative, 3D effect used egg yolk in the mixture. 

However, one researcher pointed out that there had not been any need for the egg yolk in order to create the same effect. To that end, he shared that the 30:70 ratio of raw linseed oil and lead white creates the perfect impasto paint, offering a plausible alternative recipe to what was previously assumed to be used.

   

Tagged categories: Artists; Asia Pacific; Coating Application - Commercial; Coating chemistry; Coating Materials; Coating Materials; Coatings; Coatings Technology; Colleges and Universities; Decorative Finishes; EMEA (Europe, Middle East and Africa); Historic Preservation; Latin America; Murals; Murals; North America; Paint; Paint analysis; Research and development; Z-Continents

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