The yolk of fresh hens’ eggs used as a binder for fine and thin brushstrokes, from about 1250-1500, and revived in 19th and 20th centuries.
Uccello
It was the patrons who funded, enabled, and occasionally directed the movement towards realism and secular subjects, and developed the genres.
In the Renaissance, while oil painting was still catching on, many of the greatest masterpieces were painted in egg tempera. How, and to what effect?
One of the earliest synthetic pigments, it was widely used throughout Europe, India, and Asia. But like lead white, it is seriously toxic.
The Eclectic Light Company 