After the washes completely dried to the eye (and to the touch), a series of overlapping geometric shapes are drawn. One square shape in each example is painted using the exact same mix of paint. Although the mix is no darker, the result is a darker patch of blue. This is because as sunlight passes through the extra layer of glaze, more light is absorbed by the suspended particles of pigment. Finally the overlapping shapes are painted in, resulting in a darker shape where the two overlap.