Drawing material made from various soft stones or earths (or lately from synthetic equivalents). There are three main types of natural chalk: black chalk (made from stones such as carbonaceous shale); red chalk, also called sanguine (made from red ochre or other red earths); and white chalk (made from various limestones). Chalk drawings are known from prehistoric times, but the medium really came into its own in the late 15th century, especially in the hands of Leonardo, who made many drawings in red and black chalk. Some artists, notably Watteau, used black, red, and white chalks in the same drawing. Synthetic, or ‘fabricated’, chalks are made from powdered pigments mixed with a binding medium, then rolled or pressed into sticks and dried. They were in use by the 17th century, but were not common until the 18th century. Fabricated chalks are not always clearly distinguished from crayons and pastels, and there is much ambiguity in the historical literature of the subject. However, crayons, as the term is now generally understood, are sticks of colour made with an oily or waxy binding substance, and pastels are sticks of powdered pigment bound with gum, producing a softer, more powdery effect than chalk.