Tempera painting, or egg tempera, is made by mixing egg yolk, pigments and water. This mixture, whose binder is the egg yolk and thinner is the water, is worked with the tip of the brush on a panel coated with a traditional gesso* primer. There is no broad stroke and impasto with this technique. An egg tempera painting is realized by using fine strokes, slowly, a process not for impatient minds. When finished, the dried paint film does not become yellow but extraordinarily hard with a matte finish that distinguishes it from oil painting.
[*] It is important to distinguish the traditional gesso, the mixture of rabbit skin glue and chalk, from the acrylic gesso found on the market. Acrylic gesso is a polymer that does contain any chalk. The name gesso is a deceptive element in this primer whose qualities of being impregnated and adhering to the paint film have nothing to do with those of traditional gesso. Acrylic gesso is squarely unsuitable for tempera and dubious for oil. Its quality is to dry in 30 minutes, instead of two weeks for the traditional method, explain why this process is widely used today as a primer for oil painting.