Drawing is the process of making marks on a surface by applying pressure from or moving a tool on the surface. These marks may represent what the artist sees when drawing, a remembered or imagined scene or abstraction, or, in the case of automatic drawing, may have much to do with the automatic motion of the artist's hand across the paper (or other surface). (In the process of entoptic graphomania, in which dots are made at the sites of impurities or shifts in colour in a blank sheet of paper, and lines are then made between the dots, superficially speaking the subject of the drawing is the paper itself.) The main techniques used in drawing are: line drawing, hatching, crosshatching, random hatching, scribbling, stippling, and blending.
Common drawing tools are pencils, chalk, charcoal, crayons, pastels, and pen and ink. Many drawing materials are not water or oil based and are applied dry, without any preparation. Water-based drawing media (e.g., "watercolor pencils") exist, which can be drawn with like ordinary pencils, then moistened with a wet brush to get various effects. There are also oil-based pastels and wax-based crayons. Very rarely, artists have drawn with (usually decoded) invisible ink.
The colors of drawing media can mix on the surface because of direct chemical interaction. More usually, the mixing is optical rather than chemical: colors are overlaid (also known as glazing) on previous layers so that light reflected from below the surface comes through, or color strokes are close enough that the eye "mixes" them.
Some artists have started referring to pastel and colored-pencil compositions as "paintings".