Andrew Wyeth was an American realist painter who worked primarily in the medium of tempera. Tempera is a painting technique that uses pigment mixed with egg yolk and water to create a paint that is applied to a surface such as paper or canvas. It is known for its bright colors and durability, and has been used since ancient times. Andrew Wyeth was known for his use of tempera in his paintings, which often depicted rural life in Pennsylvania and Maine.