Reflection, augmented shadow, and simple shadow's darkness
How reflected light strengthens or weakens a shadow, and when two shadows are equally dark
This page treats the nature of shadow and its reflection within the Treatise on Painting. Leonardo states that no shadow is without reflection, which strengthens it when born of something darker than the shadow and weakens it when born of something lighter. He defines the augmented shadow (a luminous, b c primitive, d g originated) and argues that a simple primitive shadow (d e) and a simple derivative shadow (f g) are of equal darkness, since both are deprived of light and reflection — invoking the principle that darkness is the privation of light. Two small hatched triangular diagrams sit among the text.
On this page
Every shadow is altered by reflection
No shadow exists without reflection, which either augments or weakens it. The reflection that augments a shadow is born from something darker than the shadow itself, while the reflection that weakens it is born from something lighter than the shadow.
The augmented shadow (a, b c, d g)
The augmented shadow is the one in which only its own derivative shadow reflects. Leonardo lays out the case with a as the luminous, b c as the primitive or original shadow, and d g as the originated shadow.
Simple shadows are equally dark (d e, f g)
A simple primitive shadow d e and a simple derivative shadow f g are of equal darkness. Since darkness is the privation of light, a simple shadow receives no illuminated reflection and stays tenebrous: d e sees neither the light a nor the derivative shadow f g, so both, deprived of light and luminous reflection, are equally dark.
Hatched triangular light-and-shadow diagrams
Two small hatched pen figures are inset in the text: an upper triangle lettered a, b, d with c below, and a lower triangle lettered a, d, b with c below, showing the light source, the shadowing body and the projected simple shadow used in the proofs.