Painter's base layer is a material known as gesso, which is a white paint mixture made of a binder mixed with chalk, gypsum, pigment, or any combination of these. Gesso is used to prime surfaces such as canvas, wood, and metal, providing a base for the paint to adhere to. It also provides a more even texture for the paint to be applied on. Gesso is an essential part of the painting process, as it helps to create a strong foundation for the artwork.