Egg Tempera as a Medium
Egg tempera is one of the earliest mediums used to bind colours to a surface. Until the introduction of oil painting in the middle of the 14th Century, egg tempera was the principal medium used for painting.
There are various formulae in the books on the subject, some involving the use of the whole egg, combined with water, varnish, and linseed oil, in varying proportions. I experimented with these when I began working with the medium in 1978.
After reading Cennini's 15th century book "The Practice of Tempera Painting" (Dover Publications, Translated by D.V. Thompson) I simplified my materials to egg yolk, water, and pigments. All pigments are mineral-based, and are light-fast and non-fugitive.
Egg yolk is a natural emulsion of oils and water, which dries clear, and remains elastic. It is tremendously tough. (Old housepainters used to add egg yolks to oil-based enamels, to toughen the paint on counter-tops!) From all reports it is more durable than linseed oil. Certainly all early tempera works I have seen in European Galleries are in beautiful shape. In fact, it was a Botticelli painting in the National Gallery in London, England, that caused me to begin learning the craft of using it.
Egg yolk dries immediately to the touch, but takes six months to oxidize fully. After the oil in the medium is fully dry the paint is waterproof, and brittle. This is the reason for painting on panels, as a stiff ground prevents cracking with humidity changes. (An oil painting takes twenty years to fully dry, after which it too is brittle, and will crack with humidity changes if painted on canvas that is poorly mounted on a stretcher.) Most of the Renaissance paintings were done on wood panels, or on canvases with up to ¼ inch of gesso surfacing.
The gesso ground under these paintings is also of traditional materials: rabbit-skin glue, calcium carbonate (chalk), titanium white pigment, and a small amount of boiled linseed oil.
The Permanence of Tempera Painting
Given good workmanship and good
materials, and a reasonably healthy environment, a tempera painting may be
expected to keep its essential character unchanged for centuries.
(from THE PRACTICE OF TEMPERA
PAINTING, Daniel V. Thompson, Jr.
The Craftsman's Handbook "Il Libro dell'Arte", Cennino d'Andrea Cennini, translated by Daniel V. Thompson, Jr., Dover Publications, New York.
The Practice of Tempera Painting (based on Cennini's writings), translated by Daniel V. Thompson, Jr., Dover Publications, New York
The Materials of the Artist & their Use in Painting, Max Doerner, translated by Eugen Neuhaus, Harcourt, Brace & World, Inc.
The Artist's Handbook of Material and Techniques, Ralph Mayer, The Viking Press, New York