The Grounds of a Picture and How to Judge a Painting
Convex edges against their ground, making bodies stand forward, and the first tests of a painter's work
Closing the wall demonstration, the page notes that although the wall a c cuts the two visual pyramids equally, with two eyes the objects never appear at equal distance. A section titled Painting a. argues that the grounds (campi) are the principal part of a picture: the convex edges of bodies are read against their grounds because they are lit differently and so appear lighter or darker, and a good painter must avoid giving an edge the very colour of its ground, since his aim is to make bodies stand forward. A further heading opens the rules for judging a painter's work, beginning with whether the figures have the relief that site and light require and whether shadows differ at the edges of the scene from those at its centre. The page is text only.
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The grounds (campi) as the principal part of painting
The grounds of painted things are the most principal part of painting, for against them the convex edges of natural bodies are recognized even when body and ground share a colour. The painter must not let an edge take the colour of its ground, since that would hide the figure and defeat his aim of making bodies stand forward from the ground.
Convex edges lit differently from their ground
A convex edge is not lit in the same way as the ground behind it, so it is often lighter or darker than that ground and can therefore be read as a separate figure. Only when edge and ground are of one colour does the boundary become indistinguishable.
Judging a painter's work: relief and placement of shadows
First consider whether the figures have the relief that their site and illuminating light demand, and whether the shadows at the outer parts of the scene differ from those at its centre. It is one thing to be surrounded by shadows and another to have shadows on one side only.