Reflection in Water; Grounds Suited to Light and Shade
Equal angles of incidence and reflection; a dark figure needs a pale ground, and a pale figure a dark one.
Continuing the argument, this leaf of the Treatise on Painting closes the demonstration that a straight sightline p d passes through more air than the oblique p s. It then treats things mirrored in landscape water, stating the law that air reflects to the eye only where the angle of incidence equals the angle of reflection, illustrated by a small semicircular figure drawn into the column. Further chapters set out how the interposed medium diminishes color, and rule that a color should meet a strongly contrasting ground, dark against light and light against dark.
On this page
Angle of incidence equals angle of reflection
Only that air gives an image of itself on the water which reflects to the eye between equal angles, the angle of incidence being equal to the angle of reflection. A small semicircular diagram in the column illustrates the reflected ray.
The interposed medium dims natural color
A visible thing shows the less of its natural color the greater the thickness of the medium interposed between it and the eye. This underlies the fading of distant color in a painted scene.
Contrast a figure's edge against its ground
Grounds separate a figure best when most varied from it: a dark color should not border another dark color but a white or whitish one, and a white color should never end on a white ground but on one as dark as possible.
Remedy when white meets white
When a white body ends on a white ground, the whites are either equal or not; if equal, the part nearer the viewer is to be made somewhat darker at the edge, the argument continuing onto the next leaf.