CHAPTER III.
COLOR MIXTURE AND BALANCE.
+All colors grasped in the hand.+
[Ill.u.s.tration: Fig. 6.]
(54) Let us recall the names and order of colors given in the last chapter, with their a.s.semblage in a sphere by the three qualities of HUE, VALUE, and CHROMA. It will aid the memory to call the thumb of the left hand RED, the forefinger YELLOW, the middle finger GREEN, the ring finger BLUE, and the little finger PURPLE (Fig. 6). When the finger tips are in a circle, they represent a circuit of hues, which has neither beginning nor end, for we can start with any finger and trace a sequence forward or backward. Now close the tips together for white, and imagine that the five strong hues have slipped down to the knuckles, where they stand for the equator of the color Sphere. Still lower down at the wrist is black.
(55) The hand thus becomes a color holder, with white at the finger tips, black at the wrist, strong colors around the outside, and weaker colors within the hollow. Each finger is a scale of its own color, with white above and black below, while the graying of all the hues is traced by imaginary lines which meet in the middle of the hand. Thus a child"s hand may be his subst.i.tute for the color sphere, and also make him realize that it is filled with grayer degrees of the outside colors, all of which melt into gray in the centre.
+Neighborly and opposite hues; and their mixture.+
(56) Let this circle (Fig. 7) stand for the equator of the color sphere with the five princ.i.p.al hues (written by their initials R, Y, G, B, and P) s.p.a.ced evenly about it. Some colors are neighbors, as red and yellow, while others are opposites. As soon as a child experiments with paints, he will notice the different results obtained by mixing them.
[Ill.u.s.tration: Fig. 7.]
First, the neighbors, that is, any pair which lie next one another, as red and yellow, will unite to make a hue which retains a suggestion of both. It is _intermediate_ between red and yellow, and we call it YELLOW-RED.[17]
(57) Green and yellow unite to form GREEN-YELLOW, blue and green make BLUE-GREEN, and so on with each succeeding pair. These intermediates are to be written by their initials, and inserted in their proper place between the princ.i.p.al hues. It is as if an orange (paragraph 9) were split into ten sectors instead of five, with red, yellow, green, blue, and purple as alternate sectors, while half of each adjoining color pair were united to form the sector between them. The original order of five hues is in no wise disturbed, but linked together by five intermediate steps.
(58) Here is a table of the intermediates made by mixing each pair:--
Red and yellow unite to form yellow-red (YR), popularly called orange.[17]
Yellow and green unite to form green-yellow (GY), popularly called gra.s.s green.
Green and blue unite to form blue-green (BG), popularly called peac.o.c.k blue.
Blue and purple unite to form purple-blue (PB), popularly called violet.
Purple and red unite to form red-purple (RP), popularly called plum.
Using the left hand again to hold colors, the princ.i.p.al hues remain unchanged on the knuckles, but in the hollows between them are placed intermediate hues, so that the circle now reads: red, yellow-red, yellow, green-yellow, green, blue-green, blue, purple-blue, purple, and red-purple, back to the red with which we started. This circuit is easily _memorized_, so that the child may begin with any color point, and repeat the series clock wise (that is, from left to right) or in reverse order.
[Footnote 17: Orange is a variable union of yellow and red. See Appendix.]
(59) Each princ.i.p.al hue has thus made two close neighbors by mixing with the nearest princ.i.p.al hue on either hand. The neighbors of red are a yellow-red on one side and a purple-red on the other. The neighbors of green are a green-yellow on one hand and a blue-green on the other. It is evident that a still closer neighbor could be made by again mixing each consecutive pair in this circle of ten hues; and, if the process were continued long enough, the color steps would become so fine that the eye could see only a circuit of hues melting imperceptibly one into another.
(60) But it is better for the child to gain a fixed idea of red, yellow, green, blue, and purple, with their intermediates, before attempting to mix pigments, and these ten steps are sufficient for primary education.
(61) Next comes the question of opposites in this circle. A line drawn from red, through the centre, finds its opposite, blue-green.[18] If these colors are mixed, they unite to form gray. Indeed, the centre of the circle stands for a middle gray, not only because it is the centre of the neutral axis between black and white, but also because any pair of opposites will unite to form gray.
[Footnote 18: Green is often wrongly a.s.signed as the opposite of red. See Appendix, on False Color Balance.]
(62) This is a table of five mixtures which make neutral gray:
{ Red & Blue-green } { Yellow Purple-blue } Opposites { Green Red-purple } Each pair of which unites { Blue Yellow-red } in neutral gray.
{ Purple Green-yellow }
(63) But if, instead of mixing these opposite hues, we place them side by side, the eye is so stimulated by their difference that each seems to gain in strength; _i.e._, each _enhances_ the other when separate, but _destroys_ the other when mixed. This is a very interesting point to be more fully ill.u.s.trated by the help of a color wheel in Chapter V., paragraph 106. What we need to remember is that the mixture of neighborly hues makes them less stimulating to the eye, because they resemble each other, while a mixture of opposite hues extinguishes both in a neutral gray.
+Hues once removed, and their mixture.+
[Ill.u.s.tration: Fig. 8.]
(64) There remains the question, What will happen if we mix, not two neighbors, nor two opposites, but _a pair of hues once removed in the circle_, such as red and green? A line joining this pair does not pa.s.s through the neutral centre, but to one side nearer yellow, which shows that this mixture falls between neutral gray and yellow, partaking somewhat of each. In the same way a line joining yellow and blue shows that their mixture contains both green and gray. Indeed, a line joining any two colors in the circuit may be said to describe their union.
A radius crossing this line pa.s.ses to some hue on the circ.u.mference, and describes by its intersection with the first line the chroma of the color made by a mixture of the two original colors.
Red & Green make Yellow-gray } Yellow Blue Green-gray } Each pair unites in a _colored_ Green Purple Blue-gray } gray, which is an intermediate hue Blue Red Purple-gray } of weak chroma.
Purple Yellow Red-gray }
+Mixture of white and black: a scale of grays.+
(65) So far we have thought only of the plane of the equator, with its circle of middle hues in ten steps, and studied their mixture by drawing lines to join them. Now let us start at the neutral centre, and think upward to white and downward to black (Fig. 9.)
[Ill.u.s.tration: Fig. 9.]
This vertical line is the _neutral axis_ joining the poles of white and black, which represent the opposites of light and darkness. Middle gray is half-way between. If black is called 0, and white is 10, then the middle point is 5, with 6, 7, 8, and 9 above, while 4, 3, 2, and 1 are below, thus making a vertical scale of grays from black to white (Chapter II., paragraph 25).
If left to personal preference, an estimate of middle value will vary with each individual who attempts to make it. This appears in the neutral scales already published for schools, and students who depend upon them, discover a variation of over 10 per cent. in the selection of middle gray. Since this VALUE SCALE underlies all color work, it needs accurate adjustment by scientific means, as in scales of sound, of length, of weight, or of temperature.
A PHOTOMETER (_photo_, light, and _meter_, a measure)[19] is shown on the next page. It measures the relative amount of light which the eye receives from any source, and so enables us to make a scale with any number of regular steps. The principle on which it acts is very simple.
[Footnote 19: Adopted in Course on Optical Measurements at the Ma.s.sachusetts Inst.i.tute of Technology. Instruments have also been made for the Harvard Medical School, the Treasury Department in Washington, and various private laboratories.]
A rectangular box, divided by a central part.i.tion into halves, has symmetrical openings in the front walls, which permit the light to reach two white fields placed upon the back walls. If one looks in through the observation tube, both halves are seen to be exactly alike, and the white fields equally illuminated. A valve is then fitted to one of the front openings, so that the light in that half of the photometer may be gradually diminished. Its white field is thus darkened by measured degrees, and becomes black when all light is excluded by the closed valve. While this darkening process goes on in one-half of the instrument, the white field in the other half does not change, and, looking into the eyepiece, the observer sees each step contrasted with the original white. One-half is thus said to be _variable_ because of its valve, and the other side is said to be _fixed_. A dial connected with the valve has a hand moving over it to show how much light is admitted to the field in the variable half.
Let us now test one of these personal decisions about middle value.
A sample replaces the white field in the fixed half, and by means of the valve, the white field in the variable half is alternately darkened and lightened, until it matches the sample and the eye sees no difference in the two. The dial then discloses the fact that this supposedly MIDDLE VALUE reflects only 42 per cent. of the light; that is to say, it is nearly a whole step too low in a decimal scale. Other samples err nearly as far on the light side of middle value, and further tests prove not only the varying color sensitiveness of individuals, but detect a difference between the left and right eye of the same person.
[Ill.u.s.tration: PHOTOMETER.
Back View. Front View.]
The vagaries of color estimate thus disclosed, lead some to seek shelter in "feeling and inspiration"; but feeling and inspiration are temperamental, and have nothing to do with the simple facts of vision.
A measured and unchanging scale is as necessary and valuable in the training of the eye as the musical scale in the discipline of the ear.
It will soon be necessary to talk of the values in each color. We may distinguish the values on the neutral axis from color values by writing them N1, N2, N3, N4, N5, N6, N7, N8, N9, N10. Such a scale makes it easy to foresee the result of mixing light values with dark ones. Any two gray values unite to form a gray midway between them. Thus N4 and N6 being equally above and below the centre, unite to form N5, as will also N7 and N3, N8 and N2, or N9 and N1. But N9 and N3 will unite to form N6, which is midway between 6 and 9.
[Ill.u.s.tration: Vertical Section through light openings.
PARTS.
_C_, CABINET, with sample-holder (H) and mirror (M), which may be removed and stored to left of dial (D) when instrument is closed for transportation.
_D_, DIAL: records color values in terms of standard white (100), the opposite end of the scale being absolute blackness (0).
_E_, EYE-PIECE: to shield eye and sample from extraneous light while color determinations are being made. Fatigue of retina should be avoided.
_G_, GEAR: actuates cat"s-eye shutter, which controls amount of light admitted to right half of instrument. Its shaft carries index-hand over dial.
_H_, FIELD-HOLDER: retains sample and standard white in same plane, and isolates them. Is hinged upon lower edge, and secured by pivot clamp.
_M_, MIRROR: permits observation of the isolated halves of the holder, bearing standard white and the color to be measured. Should be clean and free from dust on both sides of central part.i.tion.