The egg tempera painting technique is more than several centuries old. Egg tempera paint is water-soluble and fast-drying. A thin layer of paint can dry within minutes into a translucent film. It's generally not as transparent as watercolours or as opaque as gouache but can be made to appear so with the right mixture, technique, and application. Unlike oil paint, the dried egg tempera film does not yellow or darken with age; however, it tends to be brittle.
Traditionally, egg tempera was made by mixing powdered pigments with a binder made of distilled water and egg emulsion. The egg emulsion was made with either egg whites, egg yolks, or whole eggs. Later recipes added drying oils and damar varnish to improve the handling properties and resistance to cracking. The disadvantage of using drying oils, like linseed oil, is that they cause yellowing. Due to the inherent lack of plasticity, rigid support is recommended where thick layers of paints are used. Once dry, the egg tempera paint film is water-resistant and has a matte finish. The matte finish can be polished with a silk pad to increase transparency and brilliancy or varnished to resemble an oil painting.
A prepared egg tempera emulsion cannot be stored for long even in a refrigerator. Simple egg tempera paint can be made by mixing watercolour paint, distilled water, and egg-yolk emulsion in equal proportions. A drop of vinegar can be added to stop it from going bad quickly but will cause brittleness of the paint film. An egg emulsion can no longer be used when it begins to decompose. Today, egg tempera paints are available commercially in tubes doing away with the fuss of preparation and concerns over shelf life.