Egg Tempera Painting: How Solvents and Water Affect Your Work

Why This Egg Tempera Painting Study Matters in the Studio

Egg tempera painting is one of the oldest practices still in active use. It produces luminous, matte films that have survived for centuries on Italian panel paintings. However, the binder’s chemistry is not fully proteinaceous, despite the common shorthand. It contains lipids, proteins, polysaccharides, and inorganic compounds, and the lipid fraction behaves a great deal like a slow-drying oil (Casoli, Berzioli, and Cremonesi, 2012, pp. 39–40).

That fact has consequences for every egg tempera painting you produce. Tempera films age, harden, and respond to solvents and water in ways that affect both your cleaning choices and your long-term varnishing decisions. Therefore, the 2012 study by Antonella Casoli, Michela Berzioli, and Paolo Cremonesi — published in Smithsonian Contributions to Museum Conservation — deserves attention from anyone who paints in egg tempera or owns tempera works.

The authors set out to map exactly what emerges from an egg tempera painting when a swab containing water, ethanol, acetone, or isooctane is rolled across it. They tested fresh laboratory films, a seventeen-year-old reference sample, and a sixteenth-century panel painting. The results challenge a comfortable assumption: that very old tempera is essentially inert to gentle cleaning.

The Chemistry Behind Egg Tempera Painting

Painters often describe egg tempera as a protein binder. That is a useful shorthand and a misleading one. Egg yolk is dominated by lipids, with proteins playing a smaller structural role.

Yolk: A Lipid-Heavy System

Egg yolk is approximately 66% lipid by mass (Casoli et al., 2012, p. 39). These lipids exist as triglycerides (the same molecular family as drying oils), phospholipids, and cholesterol. The fatty acid distribution in yolk lipids breaks down as 38% saturated, 42% monounsaturated, and 20% polyunsaturated (Casoli et al., 2012, p. 39). Therefore, yolk has fewer reactive double bonds than linseed oil and dries more slowly through the same oxidative polymerization pathway.

Proteins are present too, and they do something that the oil in a linseed binder cannot. They provide a polymeric backbone immediately upon film formation. Consequently, fresh tempera sets up faster than fresh oil paint, even though full chemical maturation takes years.