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Egg Yolks Enhance Tempera Paint Properties
Researchers from Sorbonne University in France recently looked into why tempera paint—also known as egg tempera—was reigned as a supreme medium among Renaissance artists, such as Leonardo DaVinci, Raphael and Sandro Botticelli.
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.
Still used by artists today, the coating is noted to not mix well with other paints and requires the consistent addition of water in order to prevent drying while being used. Reports also indicate that the coating works best on solid wooden surfaces where it is less prone to cracking.
Cracking the Code
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.
Smithsonian Magazine reports that green earth was used as a skin tone underlay in Michelangelo's unfinished painting, The Virgin and Child with Saint John and Angels ('The Manchester Madonna').
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 more dense than the purely water-based coating.
It was also reported that the tempera paint provided more coverage and elasticity as well. Findings from the team’s research has since been published in the journal Angewandte Chemie.
In the future, the research team hopes that its findings can be used to better preserve tempera-based artworks.
