Quantity of Light and Shadow on Illuminated Bodies
Shadows within shadows, small versus large light sources, and why denser bodies take darker shade
A text page of the Treatise on Painting with two small circular diagrams, treating how much light and shadow a body receives. Leonardo notes that shadows made within the shaded parts of opaque bodies are faint and come from derivative, not primitive, light. A body lit by a small luminous source g keeps a large shadowed part (a d c greater than the lit a b c), while a body lit by a larger source e f is mostly illuminated (b c d greater than the shadow b a c), proved by the straightness of the rays e g, f g. A final heading states that the denser body takes the darkest shadow.
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Shadows within shadows come from derivative light
The shadows made within the shaded parts of opaque bodies are not as distinct as those made in the bodies' luminous parts, nor are they generated by primitive light, but by derivative light. Such secondary shadows are therefore weaker and softer than the primary ones.
A small light leaves a body mostly in shadow
A body is clothed with more shadow the smaller the luminous body that lights it. Let a b c d be the shadowed body and g the small light, which alone lights the part a b c, so the shadowed part a d c remains much greater than the lit part a b c. The upper of the two inset circular diagrams shows this.
A large light leaves a body mostly illuminated
A body takes more light the larger the source that lights it. Let a b c d be the illuminated body and e f the larger light: because the light so exceeds the body, the lit part b c d is far greater than the shadow b a c, proved by the rectitude of the rays e g, f g. The lower inset diagram shows this.
The denser body takes the darkest shadow
A closing heading states that a body will take shadow of greater darkness the denser it is, even when such bodies are of the same color. The section breaks off at the page foot to continue overleaf with the example of cloth and foliage.