tempera

Painting medium in which powdered pigments are mixed with a water-soluble binding agent such as egg yolk removed from its sac. It is noted for its strong, translucent colours, and can be thinned with water. In use before the introduction of oils, a form of tempera was used in ancient Egypt, and egg tempera was the foremost medium for panel painting in late medieval and early Renaissance Europe. It was gradually replaced in popularity by oils from the late 15th century onwards.

As some of its ingredients are organic, tempera may spoil and smell, although adding products such as salt and soap can help reverse or halt the growth of bacteria.

Pure egg tempera
In pure egg tempera well-ground inorganic pigments are mixed with egg yolk and water and painted onto a slightly absorbent gesso panel (a form of white plaster). Only the yellow yolk of the egg is used, as this bleaches out whereas the white of the egg may turn brown.

In early Italian painting, the initial lay-in of a design was often done with terra-verte, a greyish-green pigment. Colours were then applied to the design in a mixture with flake or zinc white, gradually being strengthened and modelled with glazes or hatches of pure transparent colour.

Tempera emulsion
Tempera emulsion uses for its medium a well-fused mixture of egg yolk and stand oil, which allows it to be diluted with water. It dries hard sooner and, being more flexible, can be used on canvas prepared with a water ground, that is, with size and gesso. The early Italian procedure is described by a pupil of Giotto, Cennino Cennini.

Casein
Casein is a variant of egg tempera in which the medium is fresh white curd and a little slaked lime, diluted with water.

In the 20th century tempera was used by US painter Andrew Wyeth.