A Color Notation Part 6

Thus stray hues from other parts of the spectrum tend to neutralize the yellow sensation, which would be strong if each of the pigments were pure in the spectral sense. Pigment absorption affects all palette mixtures, and, failing to obtain a satisfactory yellow by mixture of red and green, painters use original yellow pigments,--such as aureolin, cadmium, and lead chromate,--each of them also impure but giving a dominant sensation of yellow. Did the eye discriminate, as does the ear when it a.n.a.lyzes the separate tones of a chord, then we should recognize that yellow pigments emit both red and green rays.

White light dispersed into a colored band by one prism, may have the process reversed by a second prism, so that the eye sees again only white light. But this would not be so, did not the balance of red, green, and violet-blue sensations remain undisturbed. All our ideas of color harmony are based upon this fundamental relation, and, if pigments are to render harmonious effects, we must learn to control their impurities so as to preserve a balance of red, green, and violet-blue.

Otherwise, the excessive chroma and value of red and yellow pigments so overwhelm the lesser degrees of green and blue pigments that no balance is possible, and the colorist of fine perception must reject not alone the theoretical, but also the practical outcome of a "red-yellow-blue"

theory.

Some of the points raised in this discussion are rather subtle for students, and may well be left until they arise in a study of optics, but the teacher should grasp them clearly, so as not to be led into false statements about primary and complementary hues.

CHAPTER IV.

PRISMATIC COLOR.

+Pure color is seen in the spectrum of sunlight.+

(87) The strongest sensation of color is gained in a darkened room, with a prism used to split a beam of sunlight into its various wave lengths.

Through a narrow slit there enters a straight pencil of light which we are accustomed to think of as _white_, although it is a bundle of variously colored rays (or waves of ether) whose union and balance is so perfect that no single ray predominates.

[Ill.u.s.tration: Fig. 13.]

(88) Cover the narrow slit, and we are plunged in darkness. Admit the beam, and the eye feels a powerful contrast between the spot of light on the floor and its surrounding darkness. Place a triangular gla.s.s prism near the slit to intercept the beam of white light, and suddenly there appears on the opposite wall a band of brilliant colors. This delightful experiment rivets the eye by the beauty and purity of its hues. All other colors seem weak by comparison.

Their weakness is due to impurity, for all pigments and dyes reflect portions of hues other than their dominant one, which tend to "gray" and diminish their chroma.

(89) But prismatic color is pure, or very nearly so, because the shape of the gla.s.s refracts each hue, and separates it by the length of its ether wave. These waves have been measured, and science can name each hue by its wave length. Thus a certain red is known as M. 6867, and a certain green sensation is M. 5269.[21] Without attempting any scientific a.n.a.lysis of color, let it be said that Sir Isaac Newton made his series of experiments in 1687, and was privileged to name this color sequence by seven steps which he called red, orange, yellow, green, blue, violet, and indigo. Later a scientist named Fraunhofer discovered fine black lines crossing the solar spectrum, and marked them with letters of the alphabet from a to h. These with the wave length serve to locate every hue and define every step in the sequence. Since Newton's time it has been proved that only three of the spectral hues are _primary_; viz., a red, a green, and a violet-blue, while their mixture produces all other gradations. By receiving the spectrum on an opaque screen with fine slits that fit the red and green waves, so that they alone pa.s.s through, these two primary hues can be received on mirrors inclined at such an angle as to unite on another screen, where, instead of red or green, the eye sees only yellow.[22]

[Footnote 21: See Micron in Glossary.]

[Footnote 22: The fact that the spectral union of red and green makes yellow is a matter of surprise to practical workers in color who are familiar with the action of pigments, but unfamiliar with spectrum a.n.a.lysis. Yellow seems to them a primary and indispensable color, because it cannot be made by the union of red and green pigments. Another surprise is awaiting them when they hear that the yellow and blue of the spectrum make _white_, for all their experience with paints goes to prove that yellow and blue unite to form green. Attention is called to this difference between the mixture of colored light and of colored pigments, not with the idea of explaining it here, but to emphasize their difference; for in the next chapter we shall describe the practical making of a color sphere with pigments, which would be quite impractical, could we have only the colors of the spectrum to work with. See Appendix to preceding chapter.]

(90) A similar arrangement of slits and mirrors for the green and violet-blue proves that they unite to make blue, while a third experiment shows that the red and violet-blue can unite to make purple.

So yellow, blue-green, and purple are called secondary hues because they result from the mixture of the three primaries, red, green, and violet-blue.

In comparing these two color lists, we see that the "indigo" and "orange" of Sir Isaac Newton have been discarded. Both are indefinite, and refer to variable products of the vegetable kingdom. Violet is also borrowed from the same kingdom; and, in order to describe a violet, we say it is a purple violet or blue violet, as the case may be, just as we describe an orange as a red orange or a yellow orange. Their color difference is not expressed by the terms "orange" or "violet," but by the words "red," "yellow," "blue," or "purple," all of which are true color names and arouse an unmixed color image.

(91) In the nursery a child learns to use the simple color names red, yellow, green, blue, and purple. When familiarity with the color sphere makes him relate them to each other and place them between black and white by their degree of light and strength, there will be no occasion to revert to vegetables, animals, minerals, or the ever-varying hues of sea and sky to express his color sensations.

(92) Another experiment accentuates the difference between spectral and pigment color. When the spectrum is spread on the screen by the use of a prism, and a second prism is placed inverted beyond the first, it regathers the dispersed rays back into their original beam, making a white spot on the floor. This proves that all the colored rays of light combine to balance each other in whiteness. But if pigments which are the closest possible imitation of these hues are united on a painter's palette, either by the brush or the knife, they _make gray, and not white_.

(93) This is another ill.u.s.tration of the behavior of pigments, for, instead of uniting to form white, they form gray, which is a darkened or impure form of white; and, lest this should be attributed to a chemical reaction between the various matters that serve as pigments, the experiment can be carried out without allowing one pigment to touch another by using Maxwell discs, as will be shown in the next chapter.

(94) Before leaving these prismatic colors, let us study them in the light of what has already been learned of color dimensions. Not only do they present different values, but also different chromas. Their values range from darkness at each end, where red and purple become visible, to a brightness in the greenish yellow, which is almost white. So on the color tree described in Chapter II., paragraph 34, yellow has the highest branch, green is lower, red is below the middle, with blue and purple lower down, near black.

[Ill.u.s.tration: Fig. 15.]

(95) Then in chroma they range from the powerful stimulation of the red to the soothing purple, with green occupying an intermediate step. This is also given on the color tree by the length of its branches.

(96) In Fig. 15 the vertical curve describes the values of the spectrum as they grade from red through yellow, green, blue, and purple. The horizontal curve describes the chromas of the spectrum in the same sequence; while the third curve leaning outward is obtained by uniting the first two by two planes at right angles to one another, and sums up the three qualities by a single descriptive line. Now the red and purple ends are far apart, and science forbids their junction because of their great difference in wave length. But the mind is p.r.o.ne to unite them in order to produce the red-purples which we see in clouds at sunset, in flowers and grapes and the amethyst. Indeed, it has been done unhesitatingly in most color schemes in order to supply the opposite of green.

(97) This gives a slanting circuit joining all the branch ends of the color tree, and has been likened to the rings of Saturn in Chapter I., paragraph 17.

+A prismatic color sphere.+

(98) With a little effort of the imagination we can picture a prismatic color sphere, using only the colors of light. In a cylindrical chamber is hung a diaphanous ball similar to a huge soap bubble, which can display color on its surface without obscuring its interior. Then, at the proper points of the surrounding wall, three pure beams of colored light are admitted,--one red, another green, and the third violet-blue.

(99) They fall at proper levels on three sides of the sphere, while their intermediate gradations encircle the sphere with a complete spectrum plus the needed purple. As they penetrate the sphere, they unite to balance each other in neutrality. Pure whiteness is at the top, and, by some imaginary means their light gradually diminishes until they disappear in darkness below.

(100) This ideal color system is impossible in the present state of our knowledge and implements. Even were it possible, its immaterial hues could not serve to dye materials or paint pictures. Pigments are, and will in all probability continue to be, the practical agents of coloristic productions, however reluctant the scientist may be to accept them as the basis of a color system. It is true that they are chemically impure and imperfectly represent the colors of light. Some of them fade rapidly and undergo chemical change, as in the notable case of a green pigment tested by this measured system, which in a few weeks lost four steps of chroma, gained two steps of value, and swung into a bluer hue.

(101) But the color sphere to be next described is worked out with a few reliable pigments, mostly natural earths, whose fading is a matter of years and so slight as to be almost imperceptible. Besides, its princ.i.p.al hues are preserved in safe keeping by imperishable enamels, which can be used to correct any tendency of the pigments to distort the measured intervals of the color sphere.

This meets the most serious objection to a pigment system. Without it a child has nothing tangible which he can keep in constant view to imitate and memorize. With it he builds up a mental image of measured relations that describe every color in nature, including the fleeting hues of the rainbow, although they appear but for a moment at rare intervals.

Finally, it furnishes a simple notation which records every color sensation by a letter and two numerals. With the enlargement of his mental power he will unite these in a comprehensive grasp of the larger relations of color.

APPENDIX TO CHAPTER IV.

+Children's Color Studies.+

These reproductions of children's work are given as proof that color charm and good taste may be cultivated from the start.

FIVE MIDDLE HUES are first taught by the use of special crayons, and later with water colors. They represent the equator of the color sphere (see Plate I.),--a circle midway between the extremes of color-light and color-strength,--and are known as MIDDLE RED, MIDDLE YELLOW, MIDDLE GREEN, MIDDLE BLUE, and MIDDLE PURPLE.

These are starting-points for training the eye to measure regular scales of Value and Chroma.[23] Only with such a trained judgment is it safe to undertake the use of strong colors.[24]

[Footnote 23: See Century Dictionary for definition of chroma.

Under the word "color" will be found definitions of Primary, Complementary, Constants (chroma, luminosity, and hue), and the Young-Helmholtz theory of color-sensation.]

[Footnote 24: It must not be a.s.sumed because so much stress is laid upon quiet and harmonious color that this system excludes the more powerful degrees. To do so would forfeit its claim to completeness. A Color Atlas in preparation displays all known degrees of pigment color arranged in measured scales of Hue, Value, and Chroma.]

_Beginners should avoid Strong Color._ Extreme red, yellow, and blue are discordant. (They "shriek" and "swear." Mark Twain calls Roxana's gown "a volcanic eruption of infernal splendors.") Yet there are some who claim that the child craves them, and must have them to produce a thrill. So also does he crave candies, matches, and the carving-knife.

He covets the trumpet, fire-gong, and ba.s.s-drum for their "thrill"; but who would think them necessary to the musical training of the ear? Like the blazing bill-board and the circus wagon, they may be suffered out-of-doors; but such boisterous sounds and color sprees are unfit for the school-room.

_Quiet Color is the Mark of Good Taste._ Refinement in dress and the furnis.h.i.+ngs of the home is attractive, but we shrink from those who are "loud" in their speech or their clothing. If we wish our children to become well-bred, is it logical to begin by encouraging barbarous tastes? Their young minds are very open to suggestion. They quickly adopt our standards, and the blame must fall upon us if they acquire crude color habits. Yellow journalism and rag-time tunes will not help their taste in speech or song, nor will violent hues improve their taste in matters of color.

_Balance of Color is to be sought._ Artists and decorators are well aware of a fact that slowly dawns upon the student; namely, that color harmony is due to the preservation of a subtle balance and impossible by the use of extremes. This balance of color resides more _within_ the spherical surface of this system than in the excessive chromas which project beyond. It is futile to encourage children in efforts to rival the poppy or b.u.t.tercup, even with the strongest pigments obtainable.

Their sunlit points give pleasure because they are surrounded and balanced by blue ether and wide green fields. Were these conditions reversed, so that the flowers appeared as little spots of blue or green in great fields of blazing red, orange, and yellow, our pained eyes would be shut in disgust.

The painter knows that pigments _cannot_ rival the brilliancy of the b.u.t.tercup and poppy, enhanced by their surroundings. What is more, he does not care to attempt it. Nor does the musician wish to imitate the screech of a siren or the explosion of a gun. These are not subjects for art. Harmonious sounds are the study of the musician, and tuned colors are the materials of the colorist. Corot in landscape, and t.i.tian, Velasquez, and Whistler in figure painting, show us that Nature's richest effects and most beautiful color are enveloped in an atmosphere of gray.

_Beauty of Color lies in Tempered Relations._ Music rarely touches the extreme range of sound, and harmonious color rarely uses the extremes of color-light or color-strength. Regular scales in the middle register are first given to train the ear, and so should the eye be first familiarized with medium degrees of color.