Pastels are a popular medium used for drawing. To make pastels, gum or resin is added to pigment and formed into the shape of a small stick. When pastels are applied to a surface, the colors can appear powdery, and can be smeared or blended with the tip of a finger. When completed, pastel paintings need to be fixed with a spray or the colors can smear, though these sprays can sometimes cause discoloration. Edgar Degas and Mary Cassatt are famous impressionist artists known for their use of pastels.