Introduction – The Society of Tempera Painters
Egg tempera is a painting process that uses egg yolk to bind pigments. The artist must manufacture the paints him or herself by the simple process of mixing finely ground pigment, water and dilute egg yolk. The paint is then applied in a method where the optical laws of egg tempera are obeyed thus the unique surface of egg tempera will be achieved. In addition to making the paint the artist has also to prepare the ground on which to paint.

I have never worked with egg tempera, but this sounds very intriguing!