Tempera painting, or egg tempera, is made by mixing egg yolk, pigments and water (preferably distilled 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 (gesso means “chalk” in Italian). There is no broad stroke and impasto with this technique. An egg tempera painting is realized by using fine strokes, slowly, where the painter feels that he is embroidering. When finished, the dried paint film does not become yellow but extraordinarily hard with a matte finish that will remain intact after centuries of aging. Those who prefer matte finish prefer tempera.
So why did this process give way to oil painting in the 15th century? With the rise of easel painting, it was discovered that oil could be executed on canvas coated with white lead primer. This meant an undeniable advantage, since the traditional gesso requires a panel (or wall) made of an assembly of planks; at that time, neither plywood nor fibreboard (masonite) existed.
Today, despite the availability of panels, traditional gesso is rarely used by painters even if this primer is also excellent for oil. Why? Because its preparation requires a lot of work. You have to prepare the rabbit skin glue and wait 24 hours. If the glue reacts correctly, heat it in a water bath and add the calcium carbonate (chalk) up to the right consistency, then, while maintaining it hot, spread it on a panel (four layers on both sides of the panel). After this demanding step, leave the panel to rest for two weeks. If at the end of this period no fault appears, the panel will be considered permanent. It will then be sanded, which means another exciting day in the life of the painter. After, when its surface is smooth, it will be ready for painting tempera or oil. This new surface, similar to ivory, proven for centuries, provides a pleasant touching sensation that could convince any painter to adopt it only for this reason.
The other important asset that favors tempera instead of oil is the superposition of colors. With oil, as each pigment absorbs oil differently as consequence: each color has its own drying speed. It is therefore necessary to respect an order when superimposing a color on another. It is necessary that the ground color dries before the top color otherwise there are cracking and adhesion problems. This requirement of oil painting does not exist in tempera painting. With tempera, the painter remains free to superpose any color on any color.
 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, which, thanks to the indolence of the visual arts world, makes this process widely used today as a primer for oil painting.
 White lead is an excellent primer. However, it was replaced in the twentieth century by zinc or titanium white when it was discovered that it is a health hazard.