What is the primary artistic technique used to create the illusion of depth on flat surfaces?

The primary artistic technique used to create the illusion of depth on flat surfaces is perspective. This method involves the representation of objects in a way that mimics how the human eye perceives the world, creating a sense of three-dimensionality on a two-dimensional surface. Perspective techniques can include the use of vanishing points, where parallel lines converge, and the scale and placement of objects to suggest their relative distance from the viewer.

Chiaroscuro focuses on the contrast between light and dark to give the impression of volume and depth within a single object rather than across a scene. Fresco is a painting technique involving water-based pigments applied on freshly laid wet plaster, which does not specifically address creating depth in the way perspective does. Contrapposto refers to a pose in sculpture where the weight of the body is distributed onto one leg, which does lend a certain realism but does not translate into the depth of space across a flat surface like perspective does. Thus, perspective is the foundational technique for representing depth in two-dimensional art.