Casein is paint using milk protein as its binder — an ancient medium.
Casein paint uses casein — a protein derived from milk — as its binding medium, mixed with pigment. One of the oldest known painting media, it was used in ancient Egypt and by Roman and medieval painters, especially for tempera on wood. Casein dries quickly to a matte, porous surface with excellent tooth for subsequent layers and is highly adhesive — it has been used as glue since antiquity. Its characteristics make it well suited to precise, detailed work: fast drying, no yellowing, good stability. American illustrators of the early to mid-20th century, including N.C. Wyeth and his son Andrew Wyeth, used casein extensively for its opaque, chalky quality. In contemporary practice it is valued for its archival stability and environmental sustainability.