Giotto Cennino Cennini, a Quattrocento painter trained by students of(the artist heralded as the father of the Renaissance) is the earliest-known publisher of an egg tempera formula in his craftsman’s manual, Il Libro dell’Arte o Trattato della Pittura (The Book of the Art of Cennino Cennini). “You must temper your colors always with yolk of egg,” Cennini instructed, “[and] always as much yolk as of the colors which you temper with it.”

Hundreds of years later, yolks were discarded in favor of egg whites, which were frothed with salt and used to coat paper for mid-19th-century albumen photographic prints. “At that time, everything [in photography] relied on kitchen chemistry,” says Art Kaplan, a photography conservation scientist at the Getty Conservation Institute. “It was people at home, working and trying out different things.”

Gustave Le Gray Roger Fenton Félix Nadar After the albumen process was publicized by French photographer Louis Désiré Blanquart-Evrard in 1850, albumen prints became one of the most prevalent photographic processes of the 19th century and were used to print images by photographers fromtoand

Both media have produced works with a canonical and physical longevity that laughably contradicts the normally short shelf life of their base ingredient. But making art with eggs is not without its conservation risks. In many ways, it has proven to be a recipe for fragility.

Egg tempera paintings, for example, are much more vulnerable to the elements than their oil-painted counterparts, because their thin layers create a minimal protective film. “Embedded dirt, grime, and soot that’s generated by the atmosphere tends to bond to the surface because the paint film doesn’t have as much integrity [as oil paint],” explains Modestini. “In oil paint, the pigment particles kind of settle to the bottom and it forms an enamel on the surface which, as the linseed oil dries, becomes a much tougher film. In egg tempera, it doesn’t have this protective enamel of the medium, and the pigments are more exposed.”