Precepts on light and shadow; a body turning in fixed light
Shadow darkened by a dark object; derivative-shadow shapes; body e n lit by a moving light b
A leaf of the Treatise on Painting turning from landscape to light-and-shadow theory, with a pen diagram of a light source, a sphere and a squared object. A precept states that lights and shadows vary with their places, that a dark object added to a shadowed part deepens the shadow, and that a derivative shadow never repeats the figure of its origin unless the light matches the body's shape. A further chapter treats a human body turning in place under one light from different sides, whose shadows take infinitely many darknesses and figures; turning the body with the light fixed equals turning the light about a fixed body e n, the light being b.
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Lights and shadows vary with their places; dark objects deepen shadow
Precept: lights and shadows are as varied as the places where they are found. When the shadowed part of a body is augmented by a dark object, that shadow grows darker than before in proportion as the addition is less bright than the air.
A derivative shadow does not repeat the figure of its origin
The impact of the derivative shadow never has the figure of its primitive origin unless the primitive light is of a figure similar to the body casting the shadow. A pen diagram shows a small circle (the light) opening into a cone that meets a sphere and then a squared object.
A human body turning in fixed light yields infinite shadow shapes
Of the human body that turns about without changing place, receiving one same light from different sides and varying infinitely: the shadows clothing an irregular body take as many darknesses and figures as the varieties the body makes in its revolving motion. Turning the body with the light still equals turning the light about a fixed body; let e n be the immobile body and b the mobile light.