Tempera refers to the primary type of artist's paint and associated art techniques that were prevalent in Europe's Middle Ages. Tempera was typically created by hand-grinding dry powdered pigments into egg yolk (which was the primary binding agent or "medium"), sometimes along with other materials such as honey, milk (in the form of casein) and a variety of plant gums. When oil paint was invented in the late Middle Ages, tempera continued to be used for a while as the underpainting (base layer) with translucent or transparent oil glazes on top. This transitional, mixed technique was followed by a pure oil painting technique, which mostly replaced tempera in the 16th century.
The techniques of tempera painting can be exacting when used with traditional techniques that require the application of numerous small brushstrokes applied in a cross-hatching technique. The colors, which are painted over each other, resemble a pastel when unvarnished, or the deeper colors when varnished.
True egg tempera paintings are quite permanent. However, the term "tempera" in modern times has also been used by some manufacturers to refer to ordinary poster paint, which is a cheap form of gouache (opaque watercolor) that has nothing to do with real egg tempera.
Not to be confused with Tempura, a food.