An amateur's "anatomy of the egg"
Much of my fascination with egg tempera is its uniqueness as a material. An egg is amazing, biologically, as a prehistoric mechanism for bringing new life into the world. And its historical use by humans to communicate, record, and idolize images is profound. Working with egg tempera gives my work breath before the egg becomes paint. From the hen's natural life-giving process that produces an egg, I can mix an ideal binder. This binder holds fast pigments, some that originate from the earth and some created by modern alchemists, to a panel sourced from once-living timber. This blog post reminds the reader and me of the beautiful biological complexity that gives egg tempera artwork life.
Background
In art materials, the term "tempera" refers to any substance to which color is added to bind it to a support. Historically, the binders for tempera range from oils and waxes to glues and resins. I work with egg tempera (although I may incorporate oils in the future) because of the materials' sustainability and accessibility. As the paint's name suggests, egg (usually from a chicken) is the primary ingredient in a binder mixed with pigments. The egg tempera is applied in very thin, typically short brush strokes to a primed, rigid surface like a wood panel. [Click here to see my recipe for basic egg tempera]
Only the egg yolk is used in this process, but the other parts of the egg can still be of value. The eggshell can be dried and crushed to use as garden fertilizer or mixed into birdseed as a calcium source. The egg white can be used for cooking or to make other art materials, like glair. Below, I go into more detail about the composition and anatomy of the different parts of the egg.
Egg tempera variants
Making tempera from eggs is my preferred method of sourcing paint, and am I am fortunate to have access to the materials I choose. However, this approach isn't available or appealing to everyone.
If you want to try egg tempera and already have some painting materials (like watercolors, acrylics, or oils), check out this blog post to make tempera with materials you have. If you're a more adventurous artist than me, you can even make egg tempera from pigments you source yourself.1
You can find pre-made tubes of tempera sold by some manufacturers, although they are not composed of pure egg yolk. Instead, these products contain combinations of egg yolk, oil, and other preservatives that ultimately affect how the paint behaves. I don't have experience with tubed tempera, but famous tempera painters like Marc Chagall and Andrew Wyeth are known to have used tubed tempera.
The parts of the egg, from the outermost layer to the innermost layer, cuticula, inner membrane, air cell, albumen (egg white), chalaza, germinal disc, vitteline membrane, and yolk. © Katie Toepp 2021
Parts of the egg
cuticula
The cuticula, or shell, of the egg, is made almost entirely of calcium carbonate (CaCO3) crystals. The thousands of pores across the shell's surface allow air and moisture to pass through.
inner membrane
The inner membrane is a thin but strong protein layer that lines the shell and helps protect the egg from bacteria.
air cell
The air cell forms when the egg cools after it has been laid. As the egg ages and loses moisture and carbon dioxide, the air cell grows.
albumen
The albumen, or egg white, is made of thick and thin layers of many different proteins and water. It dries too quickly to be used in egg tempera, but it can be used for other art processes like photography.
chalaza
The chalaza are fibrous parts of the albumen that connect the eggshell's inner lining to the yolk membrane. The more prominent the chalaza is, the fresher the egg.
germinal disc
The germinal disc, or blastoderm, is a small circle where the sperm would enter the egg had it been fertilized. This embryo would grow into a fetus that then uses the yolk for nutrition.
vitelline membrane
The vitelline membrane is the thin sac that encases the yolk. The yolk should be drained and the vitteline membrane discarded when making egg tempera.
yolk
The yolk is a mixture of water, fats, proteins, vitamins, and minerals. From the Getty's Artists' Techniques and Materials,2
"Egg yolk is the ideal binder for colored pigments: the protein base gives body to the emulsion, the lipids have a plasticizing function on the paint once dry, and the lecithin is an excellent emulsifier and stabilizer; that is, it will "absorb" color, preventing its separation from the mixture and allowing for other substances to be added, such as small quantities of drying oil (to make tempera grassa)."
The yolk is the primary ingredient in our egg tempera binder. The color of the yolk can vary depending on the breed and diet of the bird. Cennini wrote that he preferred using the yolks of city hens over country hens because the color was lighter (and therefore, the brightest highlights and purest color easier achieve). I try to use sustainably sourced eggs in my work, which usually means I have little control over the yolk's color. Nevertheless, I've found a negligible discrepancy between the tempera from a bright yellow and rich orange egg.
1. Antonella Fuga, Artists' Techniques and Materials. Translated by Rosanna M. Giammanco Frongia. The J. Paul Getty Museum, Los Angeles, CA: 2006. 112
2. If you're interested in sourcing your own, natural pigments check out The Organic Artist: Make Your Own Paint, Paper, Pigments, Prints and More from Nature by Nick Neddo.