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 1st 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 Egg tempera was a primary method of painting until after 1500 when it was superseded by the invention of oil painting.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 paint which is commonly called tempera (although it is not) consisting of pigment and glue size is commonly used and referred to by some manufacturers in America as poster paint. Tempera is traditionally created by hand-grinding dry powdered pigments into a binding agent or medium, such as egg, glue, honey, water, milk (in the form of casein) and a variety of plant gums. 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.
Egg Tempera - 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 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. Once prepared, the paint cannot be stored. Egg tempera is water resistant, but not water proof. 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.
Tempera Grassa - Adding oil in no more than a 1:1 ratio with the egg yolk by volume produces a water soluble medium with many of the color effects of oil paint, although it cannot be painted thickly.
Pigments - 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.
Application
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, where as oil paints darken, yellow, and become transparent with age.
