A study of an egg tempera grassa paint formulation:
egg yolk, castor oil, water, commercial water-based car wax and commerical watercolor pigments:
The paint dries very quickly, as expected. Eye, brush and paint work together and the commercial car wax provides smoothness.
The egg yolk should be free of the egg white and the so-called 'eye'. This is the small whitish material on the egg yok sac. The sac should not enter the paint formulation demonstrated here.