Answer:
The gradual shift from light to dark is the most important effect on the finish of realistic designs, creating the illusion of the third dimension. This contrasting technique in the representation of objects is called chiaroscuro. It originated in 15th century Renaissance painting.
Mastering the transition between different shades of graphite is a challenge for beginners, who often avoid darkening areas of the drawing, making the final work pale. Or, when the opposite is true and the stroke is too strong, it results in heavy, dark designs.