A Color Notation/Chapter 5

by Albert Henry Munsell

Chapter V.

A PIGMENT COLOR SPHERE.^[1]

How to make a color sphere with pigments.

(102) The preceding chapters have built up an ideal color solid, in which every sensation of color finds its place and is clearly An image should appear at this position in the text. named by its degree of hue, value, and chroma.

It has been shown that the neutral centre of the system is a balancing point for all colors, that a line through this centre finds opposite colors which balance and complement each other; and we are now ready to make a practical application, carrying out these ideal relations of color as far as pigments will permit in a color sphere^[1] (Fig. 16).

(103) The materials are quite simple. First a colorless globe, mounted so as to spin freely on its axis. Then a measured scale of value, specially devised for this purpose, obtained by the day-light photometer.^[2] Next a set of carefully chosen pigments, whose reasonable permanence has been tested by long use, and which are prepared so that they will not glisten when spread on the surface of the globe, but give a uniformly mat surface. A glass palette, palette knife, and some fine brushes complete the list.

(104) Here is a list of the paints arranged in pairs to represent the five sets of opposite hues described in Chapter III., paragraphs 61–63:—

Color Pairs.	Pigments Used.	Chemical Nature.
Red and	Venetian red.	Calcined native earth.
and
Blue-green.	Viridian and Cobalt.	Chromium sesquioxide.
Yellow	Raw Sienna.	Native earth.
and
Purple-blue.	Ultramarine.	Artificial product.
Green	Emerald green.	Arsenate of copper.
and
Red-purple.	Purple madder.	Extract of the madder plant.
Blue	Cobalt.	Oxide of cobalt with alumina.
and
Yellow-red.	Orange cadmium.	Sulphide of cadmium.
Purple	Madder and cobalt.	See each pigment above.
and
Green-yellow.	Emerald green and Sienna.	See each pigment above.

(105) These paints have various degrees of hue, value, and chroma, but can be tempered by additions of the neutrals, zinc An image should appear at this position in the text. white and ivory black, until each is brought to a middle value and tested on the value scale. After each pair has been thus balanced, they are painted in their appropriate spaces on the globe, forming an equator of balanced hues.

(106) The method of proving this balance has already been suggested in Chapter IV., paragraph 93. It consists of an ingenious implement devised by Clerk-Maxwell, which gives us a result of mixing colors without the chemical risks of letting them come in contact, and also measures accurately the quantity of each which is used (Fig. 17).

(107) This is called a Maxwell disc, and is nothing more than a circle of firm cardboard, pierced with a central hole to fit the spindle of a rotary motor, and with a radial slit from rim to centre, so that another disc may be slid over the first to cover any desired fraction of its surface. Let us paint one of these discs with Venetian red and the other with viridian and cobalt, the first pair in the list of pigments to be used on the globe.

(108) Having dried these two discs, one is combined with the other on the motor shaft so that each color occupies half the circle. As soon as the motor starts, the two colors are no longer distinguished, and rapid rotation melts them so perfectly that the eye sees a new color, due to their mixture on the retina. This new color is a reddish gray, showing that the red is more chromatic than the blue-green. But by stopping the motor and sliding the blue-green disc to cover more of the red one, there comes a point where rotation melts them into a perfectly neutral gray. No hint of either hue remains, and the pair is said to balance.

(109) Since this balance has been obtained by unequal areas of the two pigments, it must compensate for a lack of equal chroma in the hues (see paragraphs 76, 77); and, to measure this inequality, a slightly larger disc, with decimal divisions on its rim, is placed back of the two painted ones. If this scale shows the red as occupying 34 parts of the area, while blue-green occupies 63 parts, then the blue-green must be only half as chromatic as the red, since it takes twice as much to produce the balance.

(110) The red is then grayed (diminished in chroma by additions of a middle gray) until it can occupy half the circle, with blue-green on the remaining half, and still produce neutrality when mixed by rotation. Each disc now reads 5 on the decimal scale. Lest the graying of red should have disturbed its value, it is again tested on the photometric scale, and reads 4.7, showing it has been slightly darkened by the graying process. A little white is therefore added until its value is restored to 5.

(111) The two opposites are now completely balanced, for they are equal in value (5), equal in chroma (5), and have proved their equality as complements by uniting in equal areas to form a neutral mixture. It only remains to apply them in their proper position on the sphere.

(112) A band is traced around the equator, divided in ten equal spaces, and lettered R, YR, Y, GY, G, BG, B, PB, P, and RP (see Fig. 18). This balanced red and blue-green are applied with the brush to spaces marked R and BG, care being taken to fill, but not to overstep the bounds, and the color laid absolutely flat, that no unevenness of value or chroma may disturb the balance.

(113) The next pair, represented by Raw Sienna and Ultramarine, is similarly brought to middle value, balanced by equal areas on the Maxwell discs, and, when correct in each quality, is painted in the spaces Y and PB. Emerald Green and Purple Madder, which form the next pigment pair, are similarly tempered, proved, and applied, followed by the two remaining pairs, until the equator of the globe presents its ten equal steps of middle hues.

An equator of ten balanced hues.

An image should appear at this position in the text.

(114) Now comes the total test of this circult of balanced hues by rotation of the sphere. As it gains speed, the colors flash less and less, and finally melt into a middle gray of perfect neutrality. Had it failed to produce this gray and shown a tinge of any hue still persisting, we should say that the persistent hue was in excess, or, conversely, that its opposite hue was deficient in chroma, and failed to preserve its share in the balance.

(115) For instance, had rotation discovered the persistence of reddish gray, it would have proved the red too strong, or its opposite, blue-green, too weak, and we should have been forced to retrace our steps, applying a correction until neutrality was established by the rotation test.

(116) This is the practical demonstration of the assertion (Chapter I., paragraph 8) that a color has three dimensions which can be measured. Each of these ten middle hues has proved its right to a definite place on the color globe by its measurements of value and chroma. Being of equal chroma, all are equidistant from the neutral centre, and, being equal in value, all are equally removed from the poles. If the warm hues (red and yellow) or the cool hues (blue and green) were in excess, the rotation test of the sphere would fail to produce grayness, and so detect its lack of balance.^[3]

A chromatic tuning fork.

(117) The five principal steps in this color equator are made in permanent enamel and carefully safeguarded, so that, if the pigments painted on the globe should change or become soiled, it could be at once detected and set right. These five are middle red (so called because midway between white and black, as well as midway between our strongest red and the neutral centre), middle yellow, middle green, middle blue, and middle purple. They may be called the chromatic tuning fork, for they serve to establish the pitch of colors, as the musical tuning fork preserves the pitch of sounds.

Completion of a pigment color sphere.

(118) When the chromatic tuning fork has thus been obtained, the completion of the globe is only a matter of patience, for the An image should appear at this position in the text. same method can be applied at any level in the scale of value, and a new circuit of balanced hues made to conform with its position between the poles of white and black.

(119) The surface above and below the equatorial band is set off by parallels to match the photometric scale, making nine bands or value zones in all, of which the equator is fifth, the black pole being 0 and the white pole 10.

(120) Ten meridians carry the equatorial hues across all these value zones and trace the gradation of each hue through a complete scale from black to white, marked by their values, as shown in paragraph 68. Thus the red scale is R¹, R², R³, R⁴, R⁵ (middle red), R⁶, R⁷, R⁸, and R⁹, and similarly with each of the other hues. When the circle of hues corresponding to each level has been applied and tested, the entire surface of the globe is spread with a logical system of color scales, and the eye gratified with regular sequences which move by measured steps in each direction.

(121) Each meridian traces a scale of value for the hue in which it lies. Each parallel traces a scale of hue for the value at whose level it is drawn. Any oblique path across these scales traces a regular sequence, each step combining change of hue with a change of value and chroma. The more this path approaches the vertical, the less are its changes of hue and the more its changes of value and chroma; while, the nearer it comes to the horizontal, the less are its changes of value and chroma, while the greater become its changes of hue. Of these two oblique paths the first may be called that of a Luminist, or painter like Rembrandt, whose canvases present great contrasts of light and shade, while the second is that of the Colorist, such as Titian, whose work shows great fulness of hues without the violent extremes of white and black.

Total balance of the sphere tested by rotation on any desired axis.

(122) Not only does the mount of the color sphere permit its rotation on the vertical axis (white-black), but it is so hung that it may be spun on the ends of any desired axis, as, for instance, that joining our first color pair, red and blue-green. With this pair as poles of rotation, a new equator is traced through all the values of purple on one side and of green-yellowon the other, which the rotation test melts in a perfect balance of middle gray, proving the correctness of these values. In the same way it may be hung and tested on successive axes, until the total balance of the entire spherical series is proved.

(123) But this color system does not cease with the colors spread on the surface of a globe.^[4] The first illustration of an orange filled with color was chosen for the purpose of stimulating the imagination to follow a surface color inward to the neutral axis by regular decrease of chroma. A slice at any level of the solid, as at value 8 (Fig. 19), shows each hue of that level passing by even steps of increasing grayness to the neutral gray N⁸ of the axis. In the case of red at this level, it is easily described by the notation R 8/3, R 8/2, R 8/1, of which the initial and upper numerals do not change, but the lower numeral traces loss of chroma by 3, 2, and 1 to the neutral axis.

(124) And there are stronger chromas of red outside the surface, which can be written R 8/4, R 8/5, R 8/6, etc. Indeed, our color measurements discover such differences of chroma in the various pigments used, that the color tree referred to in paragraphs 34, 35, is necessary to bring before the eye their maximum chromas, most of which are well outside the spherical shell and at various levels of value. One way to describe the color sphere is to suggest that a color tree, the intervals between whose irregular branches are filled with appropriate color, can be placed in a turning lathe and turned down until the color maxima are removed, thus producing a color solid no larger than the chroma of its weakest pigment. (See illustration facing page 32.)

Charts of the color solid.

(125) Thus it becomes evident that, while the color sphere is a valuable help to the child in conceiving color relations, in uniting the three scales of color measure, and in furnishing with its mount an excellent test of the theory of color balance, yet it is always restricted to the chroma of its weakest color, the surplus chromas of all other colors being thought of as enormous moun- tams built out at various levels to reach the maxima of our pigments.

(126) The complete color solid is, therefore, of irregular shape, with mountains and valleys, corresponding to the inequalities of pigments. To display these inequalities to the eye, we must prepare cross sections or charts of the solid, some horizontal, some vertical, and others oblique.

(127) Such a set of charts forms an atlas of the color solid, enabling one to see any color in its relation to all other colors, and name it by its degree of hue, value, and chroma. Fig. 20 is a horizontal chart of all colors which present middle value (5), and describes by an uneven contour the chroma of every hue at this level. The dotted fifth circle is the equator of the color sphere, whose principal hues, R 5/5, Y 5/5, G 5/5, B 5/5, and P 5/5, form the chromatic tuning fork, paragraph 117.

(128) In this single chart the eye readily distinguishes some three hundred different colors, each of which may be written by its hue, value, and chroma. And even the slightest variation of one of them can be defined. Thus, if R 5/6 (middle red) were to fade slightly, so that it was a trifle lighter and a trifle weaker than the enamel, it would be written R 5.1/4.9, showing it had lightened by 1 per cent. and weakened by 1 per cent. The discrimination made possible by this decimal notation is much finer than our present visual limit. Its use will stimulate finer perception of color.

(129) Such a very elementary sketch of the Color Solid and Color Atlas, which is all that can be given in the confines of this small book, will be elsewhere presented on a larger and more complete scale. It should be contrasted with the ideal form composed of prismatic colors, suggested in the last chapter, paragraphs 98, 99, which was shown to be impracticable, but whose ideal conditions it follows as far as the limitations of pigments permit.

(130) Besides its value in education as setting all our color notions in order, and supplying a simple method for their clear expression, it promises to do away with much of the misunder- standing that accompanies the every-day use of color.

(131) Popular color names are incongruous, irrational, and often ludicrous. One must smile in reading the list of 25 steps in a scale of blue, made by Schiffer-Muller in 1772 :—

1. 1. White pure.
   2. White silvery or pearly.
   3. White milky.
2. 1. Bluish white.
   2. Pearly white.
   3. Watery white.
3. 1. Blue being born.
4. 1. Blue dying or pale.
5. 1. Mignon blue.
6. 1. Celestial blue, or sky-color.
7. 1. Azure, or ultramarine.
   2. Complete or perfect blue.
   3. Fine or queen blue.
8. 1. Covert blue or turquoise.
9. 1. King blue (deep).
10. 1. Light brown blue or indigo.
11. 1. Persian blue or woad flower.
    2. Forge or steel blue.
    3. Livid blue.
12. 1. Blackish blue.
    2. Hellish blue.
    3. Black-blue.
13. 1. Blue-black or charcoal.
    2. Velvet black.
    3. Jet black.

The advantage of spacing these 25 colors in 13 groups, some with three and others with but one example, is not apparent; nor why ultramarine should be several steps above turquoise, for the reverse is generally true. Besides which the hue of turquoise is greenish, while that of ultramarine is purplish, but the list cannot show this; and the remarkable statement that one kind of blue is “hellish,” while another is “celestial,” should rest upon an experience that few can claim. Failing to define color-value and color-hue, the list gives no hint of color-strength, except at C and D, where one kind of blue is “dying” when the next is “being born,” which not inaptly describes the color memory of many a person. Finally, it assures us that Queen blue is “fine” and King blue is “ deep.”

This year the fashionable shades are “burnt onion” and “fresh spinach.” ‘The florists talk of a “pink violet” and a “green pink.” A maker of inks describes the red as a “true crimson scarlet,” which is a contradiction in terms. These and a host of other names borrowed from the most heterogeneous sources, become outlawed as soon as the simple color terms and measures of this system are adopted.

Color anarchy is replaced by systematic color description.

Appendix to Chapter V.

Color schemes based on Brewster’s mistaken theory.

Runge, of Hamburg (1810), suggested that red, yellow, and blue be placed equidistant around the equator of a sphere, with An image should appear at this position in the text. white and black at opposite poles. As the yellow was very light and the blue very dark, any coherency in the value scales of red, yellow, and blue was impossible.

Chevreul, of Paris (1861), seeking uniform color scales for his workmen at the Gobelins, devised a hollow cylinder built up of ten color circles. The upper circle had red, yellow, and blue spaced equidistant, and, as in Runge’s solid, yellow was very light and blue very dark. Each circle was then made “one-tenth” darker than the next above, until black was reached at the base. Although each circle was supposed to lie horizontally, only the black lowest circle presents a level of uniform values.

Yellow values increase their luminosity thrice as fast as purple values, so that each circle should tilt at an increasing angle, and the upper circle of strongest colors be inclined at 60° to the black base. Besides this fault shared with Runge’s sphere, it falls into another by not diminishing the size of the lower circles where added black diminishes the chroma.

Desire to make colors fit a chosen contour, and the absence of measuring instruments, cause these schemes to ignore the facts of color relation. Like ancient maps made to satisfy a conqueror, they amuse by their distortion.

Brewster’s mistaken theory underlies these schemes, as is also the case with Froebel’s gifts, whose color balls continue to give wrong notions at the very threshold of color education. As pointed out in the Appendix to Chapter III., the “ red-yellow-blue” theory inevitably spreads the warm field of yellow-red too far, and contracts the blue field, so that balance of color is rendered impossible, as illustrated in the gaudy chromo and flaming bill-board.

These schemes are criticised by Rood as “not only in the main arbitrary, but also vague”’; and, although Chevreul’s charts were published by the government in most elaborate form, their usefulness is small. Interest in the growth of the present system, because of its measured character, led Professor Rood to give assistance in the tests, and at his request a color sphere was made for the Physical Cabinet at Columbia.

1. Patented Jan. 9,1900.
2. See paragraph 65.
3. Such a test would have exposed the excess of warm color in the schemes of Runge and Chevreul, as shown in the Appendix to this chapter.
4. No color is excluded from this system, but the excess and inequalities of pigment chroma are traced in the Color Atlas.