Tempera, also known as egg tempera, is a permanent fast drying painting medium consisting of colored pigment mixed with a water-soluble binder medium (usually a glutinous material such as egg yolk or some other size). Tempera also refers to the paintings done in this medium. Tempera paintings are very long lasting, and examples from the first centuries AD still exist. Egg tempera was a primary method of painting until after 1500 when it was superseded by the invention of oil painting. A version of tempera consisting of pigment and glue size is commonly used and referred to by some manufacturers in America as poster paint.
Tempera painting has been found on early Egyptians sarcophagi decorations. Many of the Fayum mummy portraits use tempera, sometimes in combination with encaustic. The art technique was known from the classical world, where it appears to have taken over from encaustic painting and was the main medium used for panel painting and illuminated manuscripts in theByzantine world and Medieval and Early renaissance Europe. Tempera painting was the primary panel painting medium for nearly every painter in the European Medieval and Early renaissance period up to 1500. For example, every surviving panel painting by Michelangelo is egg tempera.
Oil paint, which may have originated in Afghanistan between the 5th and 9th Centuries and migrated westward in the Middle Ages eventually superseded tempera. Oil replaced tempera as the principal medium used for creating artworks during the 15th century in Early Netherlandish painting in northern Europe. Around the year 1500, oil paint replaced tempera in Italy. In the nineteenth and twentieth centuries there were intermittent revivals of tempera technique in Western art, among the Pre-Raphaelites, Social Realists, and others. Tempera painting continues to be used in Greece and Russia where it is the required medium for Orthodox icons.
Tempera painting starts with placing a small amount of the pigment paste onto a palette, dish or bowl and adding about an equal volume of the binder and mixing. Some pigments require slightly more binder, some require less. Distilled water is added.
The most common form of classical tempera painting is "egg tempera". For this form most often only the contents of the egg yolk is used. The white of the egg and even the membrane of the yolk are discarded (the membrane of the yolk is dangled over a receptacle and punctured to drain off the liquid inside).
The paint mixture has to be constantly adjusted to maintain a balance between a "greasy" and "watery" consistency by adjusting the amount of water and yolk. As tempera dries, the artist will add more water to preserve the consistency and to balance the thickening of the yolk on contact with air.
Different preparations use the egg white or the whole egg for different effect. Other additives such as oil and wax emulsions can modify the medium. Adding oil for instance in no more than a 1:1 ratio with the egg yolk by volume will produce a water soluble medium with many of the color effects of oil paint, although it cannot be painted thickly.
Some of the pigments used by medieval painters, such as Vermilion (made from cinnabar, a mercury ore), are highly toxic. Most artists today use modern synthetic pigments, which are less toxic but have similar color properties to the older pigments. Even so, many (if not most) modern pigments are still dangerous unless certain precautions are taken; these include keeping pigments wet in storage to avoid breathing their dust.
Tempera paint dries rapidly. It is normally applied in thin, semi-opaque or transparent layers. Tempera painting allows for great precision when used with traditional techniques that require the application of numerous small brush strokes applied in a cross-hatching technique. When dry, it produces a smooth matte finish. Because it cannot be applied in thick layers as oil paints can, tempera paintings rarely have the deep color saturation that oil paintings can achieve. In this respect the colors of an unvarnished tempera painting resemble a pastel, although the color deepens if a varnish is applied. On the other hand, tempera colors do not change over time, whereas oil paints darken, yellow, and become transparent with age.
Tempera adheres best to an absorbent ground that has a lower “oil” content than the tempera binder used (the traditional rule of thumb is “fat over lean", and never the other way around). The ground traditionally used is inflexible Italian gesso, and the substrate is usually rigid as well. Historically wood panels were used as the substrate, and more recently un-tempered masonite and modern composite boards have been employed. Heavy paper is also used.
Although tempera has been out of favor since the Late Renaissance and Baroque eras, it has been periodically rediscovered by such later artists such as William Blake, the Nazarenes, the Pre-Raphaelites, and Joseph Southall. The twentieth century saw a significant revival of tempera. European painters who worked with tempera include Giorgio de Chirico, Otto Dix, and Pyke Koch; and the medium was popular with American artists such as the Regionalist Thomas Hart Benton and his student Roger Medearis; Social Realists Isabel Bishop, Reginald Marsh, and Ben Shahn; Jacob Lawrence, Paul Cadmus, Jared French,Rudolph F. Zallinger, George Tooker, Robert Vickrey, Peter Hurd, and Andrew Wyeth.