How do low relief and high relief differ?

In sculpture, relief works are classified by how much the figures project from their supporting background surface. The primary difference between low and high relief lies in the degree of this projection and the artist's use of undercutting.12

Low Relief (Bas-Relief)

In low relief, the design projects only slightly from the background. These forms typically make contact with the background around their entire contour, and there is little to no undercutting. Because the projection is minimal, the sculptor must rely on sophisticated modeling and draftsmanship to create an impression of three-dimensional structure.12

High Relief (Alto-Relievo)

In high relief, the forms project at least half or more of their natural circumference from the background. Because these figures are more detached, they often require significant undercutting to define their shapes. In many cases, parts of the composition may be completely disengaged from the background, causing the work to approximate sculpture in the round.312

Artists often combine these techniques within a single composition to create a sense of depth, using high relief for foreground elements and lower relief for background features.12