of gray papers of different tones. If more than two are used they should be arranged in order from lightest to darkest. In this case each band will appear to be graded in tone from one edge to the other, each being lighter at the edge next to the darker paper.
This effect is plainly shown on the color wheel by producing several rings of grays with white and black disks of several sizes graduated from light at the center to darker at the circumference.
In consequence of this law of contrast of tone the contrast of black with active colors generally tends to intensify the black and lower the tone of the color, i. e., to weaken it as though white or light gray was mixed with it, but this effect is modified by contrast of color. Contrast of color is perceptible in black when combined with color simply because the black is not perfectly black but a very dark gray, and hence there is the same complementary effect which shows in white and the lighter grays, but in a smaller degree. This effect is most clearly seen when the color used in combination is blue or blue-green, which induces in the black, yellow or red complementaries and gives the black a "rusty" appearance.
On the other hand, for example, red with black adds the complementary green-blue to the black, which improves it. The orange and yellow have a similar effect by their blue complementaries to relieve the black from any rusty appearance and a green yellow induces a violet effect in the black.
When a color is contrasted with white the light from the pure white surface is so intense as to very largely obscure the complementary effect on the white, while on the other hand the feeble light from the black is not favorable for the exhibition of a complementary. So it might naturally be inferred that some tone between the white and black would be much more favorable than either for the observance of this effect, which is
