Ogden Nicholas Rood

“ Again, the mere contrast of dark or dull tints enhances the color and luminosity of those that are bright, and the observer receives the impression that he is gazing at a mass of gay and beautiful coloring, scarcely noticing the presence of the much larger quantity of tints that are darkened by being in deep shade. ”

“ It is quite certain that vast multitudes of still shorter waves exist, but we are deaf and blind to them; in us they excite no sensation. At this point there begins for us a great blank, in which, as Prof. Peirce once remarked, there is room for the play of not less than a dozen new senses, each as extensive as that of sight. Crossing, in imagination, this vast, unknown chasm, let us still pursue the shortening waves, and endeavor to trace their presence in a new region. ”

“ We have seen that when a single set of waves acts on the eye a color-sensation is produced, which is perfectly well defined, and which can be indicated with precision by referring it to some portion of the spectrum. We have also found that, when waves of light having all possible lengths act on the eye simultaneously, the sensation of white is produced. Let us suppose that by the first method a definite color-sensation is generated, and afterward by the second method the sensation of white is added to it: white light is added to or mixed with colored light. ”

“ According to our new theory, then, there are in the retina of the eye, where the pictures of external objects fall, three sets of nerves, adapted for the production of three separate, distinct sensations, which we call red, green, and violet. When, owing to any cause whatever, one of these sets of nerves is excited into action, the result is the corresponding sensation; if, for example, we act upon the last set by electricity, pressure, or by the luminous waves, the result will be the sensation of seeing violet light, even though not a ray of light of any kind has actually reached the eye. ”

“ We must expect, then, in painting, to find that neutral gray will be more altered by pale tints of red, orange, or yellow, which are slightly lighter than itself, and that the gray will be less altered by these colors when differing considerably from it in luminosity; analogous conclusions with regard to green, blue, violet, and purple, can also be drawn. Saturated or intense colors in a painting have less effect on white or gray than colors that are pale; this was shown in the preliminary experiment when gray was placed on a ground of strong color. ”

“ The series of tints just mentioned is now on the screen, and, were it worth while, the existence of systems of invisible waves upon either side could easily be demonstrated. The statements that I have made lead us, however, a little unexpectedly to a remarkable conclusion. They show that the beautiful colors now displayed have no existence outside of ourselves—that, outside of ourselves, there are merely waves, longer or shorter. Color is a sensation existing merely in ourselves. ”

“ The pleasure due to helpful contrast is not merely owing to the fact that the colors appear brilliant or saturated, but that they have been so disposed and provided with such companions that they are made to glow with more than their natural brilliancy. Then they strike us as precious and delicious, and this is true even when the actual tints are such as we would call poor or dull in isolation. From this it follows that paintings made up almost entirely of tints that by themselves seem modest and far from brilliant, often strike us as being rich and gorgeous in color ”

“ The specific effects produced by the mixture of white with colored light will be considered in a future chapter; it is enough for us at present to have obtained an idea of one of the constants of color, viz., its purity. The same word, it may be observed, is often used by artists in an entirely different sense: they will remark of a painting that it is noticeable for the purity of its color, meaning only that the tints in it have no tendency to look dull or dirty, but not at all implying the absence of white or gray light. ”

“ When the black square is suddenly removed, the unfatigued portion of the retina receives a powerful impulse from the red surface, but the effect produced upon the rest of the retina is inferior in degree. This accounts for the fact that the image of the square is brighter or more luminous, and we can easily understand why it is at the same time more intense or saturated in color, if we remember, as explained in Chapter IX., that red light excites into action not only the red nerves, but to a lesser extent the green and violet nerves. ”

“ Persons seeing this illusion for the first time are always much astonished. Here we have an experiment showing that the contrast produced by strong saturated tints is much feebler than with tints which are pale or mixed with white light, for, by placing tissue-paper over the green sheet, the color of the latter is extraordinarily weakened and mixed with a large quantity of white light. In this experiment it often happens that the red, which is due to contrast alone, seems actually stronger than the green ground itself. ”

“ The green nerves, of course, are not so fatigued that they do not act at all when the gray light is presented to them, but the only effect that their partial action has, is to render the rose-colored image somewhat pale or whitish in appearance. The fatigue of the optic nerve mentioned here does not differ essentially from that which it undergoes constantly even under the conditions of ordinary use, where the waste is constantly made good by the blood circulating in the retina, and by the little intervals of rest constantly occurring. ”

“ Putting this into more ordinary language, we should say simply that the strong contrast of light and shade masked such effects of harmful color-contrast as were present. There is, however, another case where we are not so indifferent or so lenient: if two objects are placed near each other in a painting, and there is good reason why both should display the same color with equal intensity, if one is painted with rich color, the other with a pale or dark shade of the same color, then the latter will look either washed out or dirty, and a bad effect will be produced. ”

“ The general effect, then, of a very bright illumination on natural objects is to cause their colors to appear paler than they otherwise would. This is, indeed, to the painter, a precious resource, for representing, in his pictures, high degrees of luminosity, and is often employed with most happy effect. According to the careful experiments by Aubert, white paper is only fifty-seven times lighter than black paper, and the painter is in the predicament of being obliged to represent the vast range of natural illumination within these very narrow limits ”

“ In point of fact, sensation does not, for the most part, increase as rapidly as the actual intensity of the light exciting it, and a point can finally be reached where sensation does not increase at all, even though the actual brightness of the light is greatly multiplied. ”

“ Let us see, if we can explain these curious changes of tint by Young's theory. The red glass used in the first experiment transmits to the eye only red light, or light capable of stimulating mainly the red nerves; but, if we increase its intensity beyond a certain point, its action on the red nerves begins to flag, and we soon have a state of things where a further increase of the red light produces no effect at all on the red nerves, they being already stimulated up to the maximum point. ”

“ I think we all know that, on dark, dull days, there seems to be a tendency to blueness in the coloring, even though we may not have paid much attention to the reverse phenomenon. All this is prettily illustrated by a very simple experiment of Helmholtz's, who noticed that the impression of a bright day was produced by merely holding a pale-yellow glass before his eyes, the tint of the glass being so faint as hardly to disturb the natural colors of the objects ”

“ Thus the presence of a pale color in a painting near that which is richer often passes unperceived, simply making the impression of a higher degree of illumination. We recognize the representation of a flood of light, and delight in it without finding fault with the pale tints, if only they are laid with decision and knowledge ”

“ We shall see hereafter that, in making chromatic compositions for decorative purposes or for paintings, artists of all times have necessarily been controlled to a considerable extent by the laws of contrast, which they have instinctively obeyed, just as children in walking and leaping obey the law of gravitation, though hardly conscious of its existence. ”

“ In some of the preceding experiments it has been seen that, as we increase the actual brightness of any colored light, red for example, so does the sensation produced also increase, but usually at a slower rate. Now, it happens that some of the sensations increase more rapidly than others; for example, the sensation for red or yellow increases more rapidly than that for blue or violet. In fact, as I said some time ago, the violet nerves always lag behind. ”

“ There are also other points of almost equal importance where the old theory is at variance with the facts of Nature; some of them will be noticed further on, but, for the present, in summing up this matter, we may say that, while the old theory answers tolerably—only indifferently well for mixture of pigments on the painter's palette—it quite fails when applied with any exactitude to the explanation or study of effects of color in Nature. ”

“ In spite of this the tints may not match, one of them being much brighter than the other, containing, say, twice as much red light and twice as much white light; having, in other words, twice as great brightness or luminosity. The only mode of causing the tints to match will be to expose the darker-colored surface to a stronger light, or the brighter surface to one that is feebler. It is evident, then, that brightness or luminosity is one of the properties by which we can* define color; it is our second color-constant. ”

“ The measurement of the amount of white light reflected along with the colored is still more troublesome, and the result likely to be somewhat less exact, while the determination of the tone, or third constant, is moderately easy under favorable circumstances. One of the uses of such determinations is the production of a set of standard colored disks with known constants, which can afterward be combined with each other, as well as with standard black or white disks, so as to generate at will, with ease and certainty, an immense number of tints whose constants will be known. ”

“ Cases of this kind often occur in large masses of foliage, which, if of the same general color, are apt in a painting to look monotonous and dull, unless great labor is bestowed in rendering the light and shade and the small differences of tint which actually exist in Nature. Under such circumstances the observer feels a certain relief at the presence of a few groups of foliage, which are decidedly paler in color than the surrounding masses, provided only there is a good excuse for their introduction. ”

“ When colored surfaces are placed near each other and compared in a natural manner, successive contrast plays an important part, and the appearance of the colors is more or less modified according to its laws. If we attempt to confine our attention to only one of the colored surfaces, this still holds good, for the eye involuntarily wanders to the other, and to prevent this requires a good deal of careful practice, for fixed vision is quite opposed to our natural habit. ”

“ The rose-red ghost which is thus developed has a color which is complementary to that which called it into existence, and this will also be the case if we employ little squares of other colors: red will give rise to a greenish-blue image, blue to a yellow, violet to a greenish-yellow, etc., the color of the image being always complementary to that which gave rise to it. ”

“ In our experiment we have merely confined the fatigue to one set of nerves, instead of distributing it equally among the three sets.
The above experiments and explanation will enable us easily to comprehend the more complicated case, where, instead of placing our little green square on gray, we lay it on a sheet of colored paper. Instead, then, of gray, let us take yellow paper, placing the green square on it as before (see Fig. 4) . ”

“ That is to say, for the sake of light and atmosphere or distance, we gladly sacrifice a large portion of the powerful tints at our disposal and consider ourselves gainers. The same is also true in another direction: we are ready to make the same sacrifice for the sake of avoiding monotony and gaining variety, provided only we can justify the act by a good reason. ”

“ If we set the amount of light reflected by white paper as 100, then a surface painted with "emerald-green" reflects about eight parts of white light; artificial ultramarine, two or three parts; red lead, seven or eight, etc. Some white light is always present; its general effect is to soften the color and reduce its action on the eye; when the proportion of white is very large, only a faint reminiscence of the original hue remains; we say the tint is greenish-gray ”

“ A result like this ought to shake, if not entirely destroy, our confidence in the old theory, but Helmholtz has pursued the investigation still further, and has proved, in addition, that the union of the pure low and blue light of the spectrum itself furnishes not green but white light. ”

“ Still, upon the whole, the effects of contrast with brilliant colors are often not strongly marked at first glance, from the circumstance that the colors, by virtue of their actual intensity and strength, are able to resist these changes, and it often requires a practiced eye to detect them with certainty. ”

“ But, if this process be for some time continued, you will soon come to a point where doubling the actual illumination produces very little effect, and finally a stage will be reached where a very great increase of actual illumination produces no additional effect on the eye at all, your paper looking no brighter than in a much feebler light. Let me make an experiment, to at least partially illustrate this: We have now upon the screen four large squares of white light, and they are, as you see, all of equal brightness. ”