Painting Techniques and Processes
Tempera is a term used to describe paint made by binding pigments in a water-based emulsion medium. In the 15th century egg yolk was often employed as this binding medium and the resulting technique was called egg tempera painting.
Colours could not be blended on the surface when using tempera, as the medium dries very quickly after each brushstroke. Each different colour had to be mixed up in the medium in advance and applied in sequence to achieve the desired modelling. A small amount of drying oil could also be added to the egg tempera for certain areas of a painting.
From the 16th century onwards, painting techniques began to change as oil painting methods were introduced from northern Europe. The new drying oil medium began to be used in preference to egg tempera. As painting practices changed, egg tempera was sometimes used for certain layers of a composition, and drying oil paints used for other layers of the same painting.