In painting, it refers to a change in value from lighter to darker (or vice versa), i.e., a change in tint or shade. It may also refer to a change in color or hue (from one color to another) or a change in temperature from warm to cool or vice versa.
There are Four Types of Edges that include: sharp, firm, soft and lost.
Sharp
Sharp, crisp, or hard edges are very contrastive and demand attention. Hard edges create the illusion of depth in contrast to soft edges. Tones with sharp edges appear to come forward, whereas tones with soft edges appear to recede in space. Sharp edges usually get our attention and are the ones in focus when we look at something.
Firm
Firm edges grab less attention than sharp edges. This is where two contrasting values have a slight or some transition from one to the other. For example, in a dramatic lighting situation, cast shadows are dark next to light areas on the same plane. However, they have softer edges as the shadow recedes into space.
Soft
Soft Edges may appear fuzzy or out of focus. These are the types of edges that we see in our peripheral vision. They do not draw the viewer's attention and may fade or blur one tone into another.
Lost
Lost Edges where two tones or colors create a gradual or smooth gradation and transition from one tone into another.
