White and black are both intensified by combination with each other, and this is the type of "contrast of tone." Contrast of tone is very clearly shown when two or more grays of different tones are placed contiguous to each other. This experiment is easily tried by mounting side by side several strips 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.
Color with Black.
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.
Colors with Gray.
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 proved by experiment to be the case. This fact is illustrated in the familiar experiment of placing a white tissue paper over black letters on a colored ground, by which the black is practically rendered a neutral gray and the color a light broken color, and in appearance the gray letters receive a color complementary to the color of the page on which they are printed. Each color has its own tone of gray most susceptible to this complementary effect. The truth of this proposition can be perfectly shown on the color wheel by forming with three different sizes of disks a gray ring on a colored surface. For example, select small disks of orange and white of equal size, then a black and a white disk of the second size and an orange and a white disk of the third size. First place the large orange and white disks on the spindle, then join the two medium-sized white and black disks and put them in front of it, and lastly add the small orange and white disks. By rotation the result is the required neutral gray ring on a light orange surface. By the joining of the white disk with each of the orange disks the orange surface may be changed to a variety of tints for trial with the different grays which may be made from the black and white disks, so that the best tones of both orange and gray may be secured. When the best proportions are obtained the effect will be surprising, because when such disks are properly adjusted the complementary effect is so strong in the gray that it appears as a very definite color, a broken green-blue. It is said that the tone of gray should have the same relation to the tone of the color that its complementary would have in order to get best results.
For the same reason if a circle of lightest neutral gray paper, say four inches in diameter, is placed on a piece of yellow paper about six inches square, and another circle just like it is put on a piece of blue paper of similar size, it will be quite difficult to convince any one who has not previously seen the experiment that both gray circles are from the same sheet of paper. The results observed in this experiment are produced by a contrast of tone which causes one to look lighter than the other, and a contrast of hue which gives one a blue and to the other a yellow hue, in contrast to the color on which it is mounted.
Contrast of Colors.
If two colors contiguous in the spectrum circuit are placed in juxtaposition the effect of the contrast of hue is to throw them away from each other. For example, if orange red and the red orange papers are put side by side the former will seem more red and the latter more orange. Therefore, when colored papers are pasted up or laid in order to form a spectrum, for example, the colors not only fail to blend together but each line of contact is very disagreeably prominent.