Ground
Tempera must be applied 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”).
Since the ground traditionally used is inflexible Italian Gesso, the substrate has to be rigid as well. Historically wood panels were used as the substrate, and more recently un-tempered masonite and modern composite boards have been employed.
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Making tempera
Place a small amount of the pigment paste onto a palette, dish or bowl.
Add about an equal volume of the egg medium and mix well making sure there are no lumps of pigment. Some pigments require slightly more egg medium, some require less.
Add distilled water (usually less than a teaspoon per egg yolk), trial and error will dictate just how much water is required.
Most often only the contents of the yolk are used. The white of the egg and the membrane of the yolk are discarded. After isolating the yolk and drying the membrane slightly by rolling it on a paper towel, pick up the yolk gently by the membrane, dangle it over a receptacle and puncture the membrane with [for instance] a toothpick to drain off the liquid inside.
If the paint contains too much yolk, the paint will look greasy and clumpy; too much water makes it run. So makers of paint have to finely adjust the amount of water and yolk to achieve a consistent paint. 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. Also 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.
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Tempera artistsMany 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 to be used without care, and precautions such as keeping pigments wet in storage must be taken to avoid breathing their dust.
Prominent egg tempera artists include nearly every painter of the Italian Renaissance before 1500 AD. For example, every surviving panel painting by Michelangelo is egg tempera. American artists of the twentieth-century revival include the Regionalist Thomas Hart Benton and Ben Shahn; Paul Cadmus, Jared French, George Tooker, Robert Vickrey, and Andrew Wyeth.
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