Hatching lines are lines drawn close together to create areas of shadow in a drawing. They are especially necessary when the drawing medium is hard pencil, marker or ink, where smudging to create shadows and variations in tone is not possible. The process of creating depth and shadow in this way is also called “cross-hatching.”
Hatching lines are usually diagonal to the picture plane and can be sets of parallel lines all going in one direction or sets of lines in opposite directions, laid on top of each other. Curved lines, particularly if they follow the shape of the object being rendered, can be useful in describing mass.