Now let us take another case. A woman, we will suppose, has a quantity of white cotton material which she proposes to dye blue. She buys some indigo, and puts it in a tub of water. Into this dye-bath she plunges the cotton, and then hangs it on a line to dry. When she has taken it down and ironed it, it presents a uniform hue of blue, its local color. But what happens when she has made it up into a dress? The local color remains the same; but the appearance is no longer of a uniform hue. In some parts the blue is paler or whiter than the local color, in other parts darker; for now the material is not spread out smoothly, the light no longer falls upon every part of it in the same way. The skirt, for example, hangs in folds; and the full light strikes directly only on the raised edges of the pleats. Into the hollow of the fold less light penetrates, and at different angles.