(Excerpts from ART HARDWARE: The Definitive Guide to Artistsí Materials, by Steven Saitzyk © 1987)
The term "tempera" comes from temper or tempering, which means to bring something to a desired, or usable, consistency. In this case, the something is a pigment. Egg tempera is one of the oldest, most versatile, and most durable methods of painting. Said to date back to prehistoric times, it is generally unaffected by humidity and temperature changes. Tempera emulsions form their own protective surface film and do not darken with age as oil paint films do. They dry rapidly and become water-resistant, which means one application of paint can be rapidly followed with another without the two layers mixing. This unique property is a distinct advantage over ordinary watercolor in that a wash of a different color may be applied over the original color without the two colors mixing to form a third. This allows you to see one color through the other. In egg tempera, a red wash may, for example, be applied over a blue wash, and the result will be a blue-red or violet, whereas the result of this procedure in watercolor will tend to appear as a muddy brown.
Tempera colors can be scraped off easily and reworked. When applied in thin layers the results are more transparent than transparent watercolor; when applied more thickly the results are opaque like gouache. After the tempera painting is completed, it can be burnished (polished) with an agate to add depth and brilliance and to increase transparency, or it can be varnished to look like an oil painting.
The first recorded recipes for egg tempera called for only the egg whites and were used for illuminating manuscripts on paper and parchment. Because this mixture is brittle, it was eventually replaced by a recipe that required only the egg yolk, which contains semidrying oils and produces a tougher, more flexible paint film. This recipe was prevalent with the Byzantine artists of the thirteenth and fourteenth centuries. In the fifteenth century, with the development of oil painting, egg-oil emulsions came into use. Soon after, egg tempera took second place to oil paints and became just a convenient medium for underpainting before the application of oil paints. Many of the old masters used a green earth tempera color underpainting in their oil paintings to create more realistic flesh tones.
Egg tempera paints are made by mixing powdered pigments with egg yolk in roughly equal parts. The pigment is first made into a paste with a small amount of water. (Some pigments, such as alizarin crimson, Prussian blue, and some blacks do not mix readily into a water paste and so a small amount of alcohol must be added as a wetting agent.) A fresh hen's egg (eggs sold in most markets are often several weeks old) and distilled water are used for the binder. To prepare the binding medium, an egg is cracked and the yolk is separated from the white. The yolk is dried by rolling it in the hand or by placing it on a sheet of absorbent paper. The yolk is then cut with a knife and the liquid allowed to run into a glass jar. Distilled water is added to bring the egg to the consistency of thin cream. The pigment paste is now mixed with the egg yolk binder and the paint is ready for use.
Tempera made with only an egg yolk is not as workable a painting medium as an egg-oil emulsion. The addition of a small amount of stand oil improves the handling properties and increases the resistance to cracking so that the paint film can be made thicker. Egg-oil emulsions can be used on flexible supports such as canvas, heavy watercolor paper, and thick bristol paper, if applied in thin layers. Thicker layers, like those used in the application of gouache, are quite safe if they are built up slowly in thin layers. Egg-oil emulsions produce a glossier finish than pure egg tempera and dry harder. Like egg tempera, an egg-oil emulsion dries very rapidly, in seconds in thin washes, and can be painted over almost immediately.
Egg-oil emulsion temperas are now being offered in tubes by the Rowney Company and the Sennelier Company. After thinning with a little distilled water, the paint can be used straight from the tube, saving the artist the inconvenience of having to prepare the color from the raw materials before each painting session.
You can prepare your own egg-oil emulsions according to the following instructions. But you should take extreme caution when using dry pigments. Egg Yolk and Linseed Oil are combined to create an egg-oil emulsion with an oil paint consistency. Mix one teaspoonful of oil with a single egg yolk. Too much oil slows the rate of drying significantly and tends to leave a tacky surface. One part of this emulsion can then be mixed with one part of waterdampened pigment.
Egg Yolk, Stand Oil, and Damar Varnish make a durable and flexible egg-oil emulsion. Mix one egg yolk and one level teaspoonful of a mixture of half stand oil and half Damar varnish. Pigment can then be added one part to one part. As with all egg or egg-oil temperas the surface can be polished with a silk pad when dry. The disadvantage of this egg-oil emulsion is that it very much resembles oil paint with its inherent yellowing; thus it has little advantage over oil paint. Venice turpentine can, however, be used as a substitute for stand oil, to reduce future yellowing and to improve the clarity of the paint film.
Whole Egg and Linseed Oil is the lazy person's egg tempera. The egg, oil, and pigment are mixed in equal portions. This egg-oil emulsion dries relatively quickly, producing a hard, but slightly cloudy, surface.
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