
“…negative space is more subtle, beginning wherever positive space ends. It is the peripheral area, the space surrounding the occupied space. …
“When you are composing negative space, remember that negative space is limited by the format of the painting surface. The shapes of the positive space, in contrast, as usually centrally located. Negative space also often needs to be broken up into smaller shapes and then integrated with the balance of the painting.”
Albert Handell and Leslie Trainor Handell, “Intuitive Composition”, page 34
Think of space in a painting the way Monet advised us not to paint objects (tree, house, field) but instead paint shapes of colour (a square of blue, an oblong of pink, a streak of yellow). The composition of a painting is not “important space” — occupied by the subject — surrounded by “empty space”, it’s all crucial to the result. Some parts may take less time to paint, but that’s a measure of time spent not importance to the composition.
When last, when a painting wasn’t working, did you contemplate the negative space in your composition?

- See also: Break Up the Sky