The Science of Shadow: Where Derived Shadow Is Darkest
A shadow reads blacker against a bright field, is darkest near its cause and at its edges, and crosses the shape of its light
A text page of the Treatise on Painting's fifth part, on the science of cast shadow. It observes that a shadow appears blacker where it borders a bright field, and that a derived shadow is darkest and most sharply bounded nearest to its cause, fading and blurring as it recedes. Further chapters argue that a shadow never truly copies the outline of its body unless the light shares that body's shape, and that a shadow's length always runs crosswise to the length of its light source.
On this page
A shadow looks blacker against a bright field
The shadow of the object b d cast upon d c appears blacker at n c, because there it borders the white field c e, than at n d, where it borders the dark field n c. The apparent darkness of a shadow depends on the brightness of the ground beside it.
Where the derived shadow is darkest and sharpest
The derived shadow is of greater darkness the nearer it lies to its cause, and grows lighter where it is remote. It is likewise more distinct and sharply bounded near its origin, and shows itself darker toward its edges than toward its middle.
A shadow's shape crosses the shape of its light
A shadow never has the true likeness of its body's outline, even were the body spherical, unless the light is of the body's shape. If the light is long and upright the shadow spreads in breadth; whatever the length of the light, the shadow's length always runs crosswise to it, like a cross.