Old Masters' Paint Contained Protein—Likely Intentionally

If Leonardo da Vinci and Rembrandt were alive today, they'd likely be wringing their hands over egg prices with the rest of us. That's because they may have intentionally added egg yolk to their oil paints, and a new study published Tuesday in Nature Communications tries to get at why. In "the first systematic study on the effect of adding proteinaceous materials to oil paints," researchers sought to understand how the addition of egg to oil paints would have impacted the artwork. The upshot: "such proteinaceous binders can be important additives." Before the why, the how:

The researchers evaluated three types of paint: a regular oil paint made from pigment and linseed oil; a version that added fresh egg yolk, giving it a mayo-like consistency; and a version in which pigment was mixed with the yolk, dried, and then mixed into oil—"a process the old masters might have used, according to the scant historical records that exist today," per the Guardian. "The addition of egg yolk is beneficial because it can tune the properties of these paints in a drastic way," study author Ophélie Ranquet tells CNN.

Ranquet says the addition slows oxidation—a process that can cause paint to yellow over time—and makes the paint less sensitive to humidity. Science News explains additional benefits: "In the mayolike blend, the yolk created sturdy links between pigment particles, resulting in stiffer paint. Such consistency would have been ideal for techniques like impasto, a raised, thick style that adds texture to art. Egg additions also could have reduced wrinkling by creating a firmer paint consistency."

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CNN points out the Old Masters' egg use was far from novel: Ancient Egyptians created tempera paint using water, pigment, and egg yolk. And while Ranquet acknowledges it's possible the very limited presence of proteins in the paint could indicate it wasn't intentionally included but was merely contamination from tempura paints kept in the artists' workshops, the researchers don't think that's the case. "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," co-author Ilaria Bonaduce tells the Guardian. (More discoveries stories.)