As his optical studies increased, Leonardo expressed doubts concerning linear perspective. While it was a logical system it did not correspond in reality to our perception of the world. In his later works, the impression of relief is the product of the optical relationship between the figure and the background, as the interaction of light and shade becomes all-important.

In St John the Baptist, Leonardo avoids the absolute definition of space by setting the figure against a dark background. A profound sensation of three-dimensional form has been created through the use of chiaroscuro.

Leonardo was aware of the inherent dangers of this system. Earlier in his notes he warned that a figure will not be discerned against a dark background and will not appear to be detached from it. From a distance nothing will be visible but the illuminated parts. However, in the shadows of the body of St John the Baptist, Leonardo has retained just enough light for us to be able to comprehend his form fully. As in the moon, even the dark areas of his figure retain a “slight glimmer” of reflected radiance.

In Leonardo's words
The first intention of the painter is to make a flat surface display a body as if modelled and separated from this plane, and he who most surpasses others in this skill deserves most praise. This accomplishment, with which the science of painting is crowned, arises from light and shade, or we may say chiaroscuro.