VIZIO 1016
`
`

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`COLOR
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`AND ITS APPLICATIONS
`
`BY
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`M. LUCKIESH
`DIRECTOR OF SP1-‘LIED SCIENCE, NELA RESEARCH LABORATORIES
`NATIONAL LAMP WORKS OF GENERAL ELECTRIC CO.
`MJTHOR OF "LIGHT AND SHADE AND THEIR APPLICATIONS." "TEE LIGHTING
`ART," “THE LANGUAGE OI? COLOR," "ARTIFICIAL LIGHT. ITS INFLUENCE
`UPON CIV]1.IZ&TION," "_LlGB'.TING THE HOME," ETC.
`
`150 Illustrations‘-"-4 Color P1a.tes—-34 Tabfles
`
`
`
`SECOND EDITION
`ENLARGED
`
`NEW YORK .
`
`D. VAN NOSTRAND COMPANY
`EIGHT WARREN STREET
`
`I 921 '
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`VIZIO 1016
`VIZIO 1016
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`

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`CONTENTS
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`CHAPTER I
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`i LIGHT . .
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`Wave Theory. Electra-magnetic Theory. Radiation and Light Sensa-
`tion. Temperature and Radiation. Spectra of Illuminants.
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`CHAPTER II
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`THE PRODUCTION OF COLOR . . .
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`28
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`Interference. Polarization. Reflection, Ab-
`Refraction. Diflraction.
`sorption, and Transinission. Color of Daylight. Color Sensations
`Produced by Colorless Stimuli. Fluorescence and Phosphorescence.
`Useful Filters.
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`CHAPTER III
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`6%
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`COLOR-MIXTURE .
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`Subtractive Method. Additive Method.
`Simple Apparatus for Mixing Colors.
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`Juxtapositionnl Method.
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`CHAPTER IV
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`coma TERMINOLOGY .
`Hue, Saturation, and Brightness. Tri-color Method. Color Notation.
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`89
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`CHAPTER V
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`THE ANALYSIS OF COLOR .
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`B5
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`The Monochromatic
`The Spectrophotometer.
`The Spectroscope.
`Colorimeter.
`The Tri-chromatic Calorimeter. Other Methods.
`Templates. Reflectometer. Methods of Altering Brightness Non-
`selectively.
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`CHAPTER VI
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`COLOR AND VISION . .
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`116
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`The Eye. Brightness Sensibility. Hue Sensibility. Saturation Sensi-
`bility. Visual Acuity in Lights of Different Colors. Growth and Decay
`of Color Sensations. Signaling. Other Uses for Colored Glasses.
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`VIZIO 1016
`VIZIO 1016
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`vi
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`CONTENTS
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`CHAPTER VII
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`THE EFFECT OF ENVIRONMENT ON COLORS. .
`]1lnm.ination. After-images. Simultaneous Contrast.
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`Irradiation.
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`163
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`CHAPTER VIII
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`THEORIES OF COLOR VISION .
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`181.
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`Young-Helmholtz.
`Green.
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`‘Duplicity.’ Hering.
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`Ladd—Franklin. Edrigde-
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`COLOR PHOTOMETRY .. .
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`CHAPTER IX
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`}
`191
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`Methods of Color Photometry. Other Means of Eliminating Color Dif-
`ferences. Direct Comparison and Flicker Methods. Luminosity
`Curve of the Eye.
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`CHAPTER X
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`COLOR PHOTOGRAPHY .
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`213
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`Lippmann Process. Wood Diffraction Process. Color Filter Processes.
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`CHAPTER XI
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`224
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`COLOR III LIGHTING .
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`Artificial Daylight. Units for Irnitating Daylight. Efiect of Colored Sur-
`roundings. Color in Interiors. Color Preference. A Demonstration
`Booth.
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`CHAPTER XII
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`COLOR. EFFECTS FOR THE STAGE AND DISPLAYS .
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`273
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`Stage. Displays.
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`CHAPTER XIII
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`282
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`COLOR PHENOMENA IN PAINTING .
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`Visual Phenomena. Lighting. Pigments.
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`CHAPTER XIV
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`COLOR MATCHING . . . .
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`302
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`The Illurninant.
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`-the Examination of Colors.
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`VIZIO 1016
`VIZIO 1016
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`

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`CONTENTS
`
`vii
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`CHAPTER XV
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`THE ART OF MOBILE COLOR .
`Color Music.
`Its Relation to Sound Music.
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`312
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`CHAPTER XVI
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`COLORED. MEDIA .
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`327
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`Available Coloring Materials. Dyeing. Gelatine Films. Solvents.
`Lacquers. Celluloid.
`Phosphorescent Materials. Miscellaneous
`Notes.
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`CHAPTER XVII
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`CERTAIN PHYSICAL ASPECTS AND DATA.
`Three Types of Colored Media. Pigments. Optical Properties of Pig-
`ments. Applications of Spectral Analyses of Pigments. Reflection-
`factorsof Pigments. Spectral Analysesof Dye-solutions. Applications
`of Spectral Analyses of Dyes. Laws Pertaining to Colored Solutions.
`Dichromafisnn. Graphical Method for Using Spectral Data. Spectral
`Analyses of Glasses. Red, Yellow, Green, Blue, and Purple Glasses.
`Use of Spectral Analyses of Glasses.
`Influence of Temperature on
`Transmission of Colored Glasses. Ultraviolet Transmission of Media.
`Compounds Sensitive to Temperature. Trsnsrnission of Light by Fog
`and Water. Color Temperature of Illuminants.
`INDEX .
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`VIZIO 1016
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`54
`Facing page
`I‘
`II
`54
`I‘
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`VIZIO 1016
`VIZIO 1016
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`COLORED PLATES
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`P1-ismatlcspoolrutn .
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`Difiraction Grating Spectrum .
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`Subtraotlve method of mixing colors .
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`Additive method of mixing colors .
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`Showing the efiect of enviromnt on the appearance of colors
`Illustrating the effect of the spectral quality of the illuminant
`Daylight, below: ordinary artificial light. above .
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`

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`CHAPTER HI
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`COLOR~MIXTURE
`
`17. That there is a tremendous variety of colors.
`present
`in Nature can hardly escape the most
`in"
`'.
`different observer. A glance at a modern painti
`reveals the same abundance of tints and shades of.
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`color created by the hand of the artist from a few-
`well-chosen fundamental colors. The artist mixes‘
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`sometimes;
`in a qualitative manner. He
`colors
`begins painting with some knowledge of the science:
`of co1or—mixture, but after all his knowledge of mixing:
`colors is largely qualitative and based upon asso-'=
`ciation with his stock of pigments rather than upon
`knowledge of quantitative mixture of spectral colors.-
`His success lies largely in a thorough acquaintance"
`- with the tools at his -disposal, which are his pigments,__
`yet an acquaintance with the science of color is of;
`incalculable value to him, for the experimental results‘
`of
`the scientific study of color.-mixture have largely
`formed the foundation of pure and applied art as
`well as of modern color theories.
`
`18. Subtractive Method. —There are two dis-"
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`tinct methods of mixing colors; by addition and by
`subtraction of
`light rays.
`In a sense, color, as We
`prdinarily encounter it,
`is produced primarily by sub-
`traction (#12). That is, a fabric appears colored as
`a rule because the chemical used in staining it has
`the property of absorbing certain visible rays and
`of
`reflecting (or
`transmitting)
`the remaining rays.
`This subtraction of colored rays from white light.
`54
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`VIZIO 1016
`VIZIO 1016
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`

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`Plate II. Fig. 20. The Subtractive Method of Mixing Colors
`
`Plate 11. Fig. 21. The Additive Method of Mixing Colors
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`VIZIO 1016
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`COLOR-MIXTURE - 55
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`results in the residual colored light. The integral
`color of
`the light absorbed is said to be comple-
`mentary to the color of
`the light remaining if the
`total light in the beginning were white light, say noon
`sunlight. Of course in the foregoing case the ab-
`sorbed color has disappeared, so there is no oppor-
`tunity to view the complementaries. Any pair of
`"complementary colors can be readily viewed by a
`comparatively simple
`apparatus. By means of a
`prism the spectrum of sunlight is produced at some
`point
`in space. A portion of this spectrum can be
`Zdeflected from the original path by means of a prism
`of slight angle. The rays in each beam can be com-
`bined upon adjacent spots of a white surface by
`means of
`lenses, :-vith the result
`that
`instead of a
`spot of white light, two adjacent spots of colored fight
`are seen. These. two colored lights are obviously
`complementary, for if they are made to overlap they
`will be found to produce, by addition, a white light.
`By separating various portions of
`the spectrum all
`the pairs of complementary colors are readily pre-
`sented to view. As will be shown later, white light
`can be matched by mixing certain pairs of (and also
`by mixing three or more) spectral colors. This can
`-readily be demonstrated by means of variable slits
`cut in a cardboard screen and held in front of the
`-spectrum.
`If
`the slits have been placed in their
`proper position in the spectrum and properly adjusted _
`--in width, white light will result when the rays from
`these slits are combined on a white screen by means
`-of a lens.
`
`The subtractive primary colors have been termed
`- red, yellow, and blue.
`In reality they would be more
`-exactly described as purple, yellow, and blue-green.
`-They are the complementaries of
`the additive pri-
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`VIZIO 1016
`VIZIO 1016
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`56 - COLOR AND ITS APPLICATIONS
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`maries, as will be seen later. Some may prefer to use
`the term ‘pink’ or ‘magenta’ instead of ‘purple’, but
`the hue is a purple consisting of red and blue. The-
`tri-color processes of printing and color photography
`are based upon the subtractive principle of mixing.
`
`If the three-
`demonstrated by Fig. 20 (Plate II).
`subtractive primaries, purple, yellow, and blue-green‘,
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`fore the light which reaches the eye is white minus;
`violet and blue rays, and produces a sensation of‘
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`scopic in size, each being a minute flake of pigment:
`If two flakes be superposed, a yellow above a blue-'
`green, a green color is obtained. The yellow flake‘
`does not transmit blue rays, therefore the green rays
`are the only remaining rays that will be transmitted
`by the blue—green pigment. These will be reflecte _
`by the white surface, and will pass again through the
`blueegreen and yellow pigments, undergoing furthe
`changes tending to purify them, so that onlygreen rays
`reach the eye.
`If the blue-green flake is above the
`yellow flake, the explanation must be reversed, but
`with the same result. The blue-green flake trans-
`mits blue and green rays; however, the yellow flake.
`does not
`transmit blue rays. Therefore, only the
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`VIZIO 1016
`VIZIO 1016
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`COLOR—MIXTURE 57
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`green rays will eventually be reflected to the eye.
`In the same manner the blue of the purple is sub-
`tracted by the yellow flake, and as purple consists of
`‘red and blue rays only,
`the red rays remain to be
`reflected to the eye. Therefore, yellow and purple
`flakes superposed produce red. Likewise the blue-
`green flake does not transmit red light, so that super-
`position of blue-green and purple flakes results in
`_ blue light being reflected to the eye.
`It is further
`seen that
`the superposition of
`the three subtrac-
`five primaries results in a total extinction of
`light
`and black is
`the result. For
`instance, where the
`yellow and purple disks overlap, red results. The
`blue-green disk does not transmit red rays, so where
`it overlaps the red disk a total extinction results.
`Much interesting information may be obtained
`by carefully studying Fig. 20. Strips of colored
`gelatine laid over each other in checkerboard fashion
`present many striking examples of
`the subtractive
`method of mixing colors.
`In ordinary artificial light,
`screens made of ethyl violet
`(purple), uranin or
`aniline yellow, and filter blue-green, are excellent
`dyes for making the subtractive primaries for demon-
`strating the foregoing by superposition. Ethyl violet
`and naphthol green ‘are practically complementary, so
`‘-that when superposed no light rays are transmitted.
`19. Additive Method.—As already
`indicated,
`there are two distinct methods of mixing color,-—
`the additive and subtractive,’-but close investiga-
`tion often reveals both processes entering into some
`part of the production of color. The additive method
`always tends toward the production of white, whereas
`the subtractive method tends toward the production
`--of black. The additive primaries are red, green, and
`blue. Some prefer to use the term ‘violet’ instead
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`53 COLOR AND ITS APPLICATIONS
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`of ‘blue.’ Blue, however, -appears satisfactory and is‘
`a safer term than violet, because there are a great.
`many who apply the term violet to purples.
`Long ago it was demonstrated that, by prope-
`mixtures of
`the three well-chosen primary colors,-
`any color can be matched. This is largely due to:
`the fact that the eye is a synthetic rather than an
`analytic instrument.
`In Fig. 21 (Plate II) are illus
`trated the principles of color-mixture by the additive
`method.
`It is seen that red added to green produces
`yellow; and further, when blue is added to this com
`bination white is produced.
`In other words, yello
`and blue mixed by addition produce white.
`It is well
`known, however,
`that yellow and blue (in reali -r:
`blue—green) pigments when mixed by the subtractiv
`method, as is done in painting. and color printing,
`produce green. This is a much confused point, bu
`is very simply explained when the character of th
`procedure of mixture is analyzed. Red and blu
`when added produce purple;
`and blue and green;
`produce blue-green.
`It 15120 be noted that combina
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`subtractive" primaries and vice versa. The additiv
`method can be readily demonstrated by the use 0:
`colored fights projected upon a white surface. Prop
`erly selected color-screens are necessary, but can b
`readily made from aniline dyes by carefully mix‘
`them.
`It is difficult to describe the procedure quan
`titatively, but there is no difliculty in producing th
`proper colors.
`Owing to the very unsatisfactory state of colo
`terminology, it is impossible to present an accurat
`and definite list of complementary hues. However,
`a few complementaries are given in Table IV.
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`59
`COLOR-MIXTURE
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`TABLE Iv
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`Complementary Hues
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`Red .
`Orange-red .
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`Yellow-green .
`Green .
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`. .Blue-green (Cyan blue)
`. .Green-blue (bluish cyan}
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`. . ..Blue
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`. .Blue—violet
`. . . .Violet-purple
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`. .PLu'pie (magenta)
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`Wave-length of Complementary Spectral Hues
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`0.6562 p.
`.607’?
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`0.4921 ,u.
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`.4354
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`.5671 p.
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`.4645 11.
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`Y
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`showing the comple-
`An excellent scheme for
`mentaries is
`to arrange the spectrum around the
`circumference of a circle filling a gapbetween the
`ends of
`the spectrum, violet and red, with a series
`of purples from bluish purple to reddish purple. This
`has been called a color wheel, and is diagrammatically
`shown in Fig. 22. Here
`yellow and violet are shown
`as complementary. This may
`appear inconsistent with the
`foregoing discussion, but it
`will be noted that the terms
`‘blue’ and ‘violet’ (as well
`-as other color names) are
`indefinite. The term ‘blue’
`
`R
`
`as
`
`V
`
`will always mean a spectral
`blue, but when used as a
`primary color its hue is defi-
`nite, whether the term stands
`If the complementaries
`for blue, violet, or blue-violet.
`have been correctly applied to the color wheel, a
`neutral gray should be obtained when it
`is rapidly
`rotated.
`
`Fig. 22.—'1‘l1e color—wheeI for show-
`ing complementary hues.
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`COLOR AND ITS APPLICATIONS
`
`
`
`
`3
`color
`a
`20. Juxtapositional Method. —-If
`broken up into its component colors and the latter +_:
`applied in small dots with the point of a brush,
`_.
`sensation of the original color will be obtained if
`be viewed from a distance at which the eye is
`able to resolve the -individual dots and providing _e
`relative areas covered by the various colored d"
`are correctly balanced. Colors, excepting those -:j_
`countered in the spectrum, are usually far from mon
`chromatic (#12),
`(Figs. 122, 123). For instance, -:2.
`colored fabric which may appear a pure red will
`found to reflect rays throughout considerable r -.5;
`of wave-lengths.
`If these component colors be repr
`sented as pure’ as possible in minute dots of prop
`relative amounts,
`the foregoing result
`is
`rea"
`obtained. For instance, if one end of a pack of car
`be painted red and the other end green, on reve
`ing every other card and viewing an end of the ri‘.
`at a distance of several feet, it will appear yellow
`color.
`The brightness apart from hue will be
`average brightness. Many interesting experimen
`can be performed by ruling alternate fine lines 5‘-
`difierent colors on paper or on glass. For instanc
`purple and green lines alternated on paper will,
`well chosen, produce an appearance of gray at -'3
`distance. Such a method of breaking a compost
`color
`into more nearly monochromatic componen.
`and applying the latter in the form of minute do._
`is the foundation of the principle of impressionis
`painting. The processes of color photography devissi
`by Joly, Lumiere and others are also based on
`v'.=.'
`principle.
`__
`for Mixing Colors.
`21. Simple Apparatus
`There are very elaborate co1or—mix:ing instrumen
`on the market for the purpose of demonstrating 53
`
`
`
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`COLOR-MIXTURE 61
`
`
`
`theory and practise of color-mixture. Apparatus that
`:_deals with spectral colors is as a rule the most sat-
`ljsfactory for accurate study and demonstration. How-
`gver,
`inasmuch as the colors ordinarily available in
`practise are far from monochromatic, that is, far from
`[spectral purity,
`there is much virtue in the simpler
`‘forms of apparatus that can be made at small. expense.
`In fact, for the foregoing reason the results obtained
`with some of
`the simpler instruments for demon-
`stration are more readily interpreted and applicable
`in practise than those obtained with apparatus dealing
`with pure spectral colors.
`MaxWel1’s disks offer a ready means for mixing
`colors. A shaft is arranged so as to be revolved at
`high speed. Colors painted on a disk "can thus be
`mixed by rotating it at a high speed owing to per-
`sistence of vision.
`Light sensations do not reach
`their full value immediately upon application of the
`stimulus, nor do they decay to zero immediately upon
`the cessation.of the stimulus. An infinite number of
`mixtures of pigments,
`including black and White,
`can be made with such a simple disk. Colored
`papers cut in circles and slit along one of the radii
`can thus be overlapped to any degree, and by the.
`,use of circles of various sizes a number of mixtures
`can be produced upon the same disk. This method
`is not truly an additive one, excepting in the addition
`of hues. The brightness is the mean of
`the sepa-
`rate bri'ghtnesses, each weighted by its angular
`extent.
`In Fig. 23 are typical color disks for mixing
`colors to produce grays.-
`In I and III are repre-
`sented pairs of complementary colors respectively,
`yellow and blue, and green and purple. The inner
`circle consists of black and white, which can be varied
`in angular amounts to produce a neutral gray to
`
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`COLOR AND ITS APPLICATIONS
`
`
`
`
`
`match the gray produced by the addition of the
`hues.
`In II are represented the three primary colo ;.
`which when mixed by rotation produce a neutr
`gray which is readily matched by means of the
`black and white disks. These matches made und_'
`one illuminant will not ordinarily remain match :5
`under another illuminant. Much of
`the early
`in the science of color was done by means of rota '
`disks and even today they are extremely valuabi,
`in some investigations. The disks represented '
`Fig. 23 can be readily made from Zimmerman"-.'.
`
`Fig. 23.——Maxwell disks.
`
`
`
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`colored papers. These papers are indicated in
`catalogue by the letters of the alphabet and are give
`herewith as used in the disks already describe
`Yellow is designated as g, blue as 0, green as 1‘, re:
`as b, and purple as a. For the black and white secto
`any neutral
`tint papers with dull
`finish are sag:-:.
`factory for producing the grays.
`-
`The additive and subtractive methods as
`
`trated in Figs. 20 and 21 (Plate II) can readily
`demonstrated in permanent charts.
`The importefi
`colored papers have been found satisfactory, ow'_
`to their comparative purity and unglazed surfacesi
`For demonstrating the subtractive method by tli
`
`

`
`I’
`
`,
`
`
`
`COLOR—MIXTU'R.E 63
`
`lman colors, designated by a, g, I, b, 1', and 0, may be
`'-‘used respectively for purple, yellow, blue-green, red,
`:-green, and blue. These six colors, with black and
`L-white, are suflicient for the construction of charts for
`|-the additive and subtractive methods. For demon-
`.-strating the additive method the three disks should
`the surrounded with black background, but
`in the
`-case of the subtractive method the background should
`the white. For demonstrating these two methods
`:of color-mixture with artificial
`light by means of
`ll}:-ansparent media, purple and green are readily
`lyproduced by using gelatines dyed with ethyl violet
`land naphthol green respectively. When these two
`"colored gelatines are superposed in proper densities
`tot coloring, no light
`is transmitted. When light
`is
`[passed through these media in juxtaposition in proper
`pg}-elative amounts and combined on a neutral
`tint
`diffusing surface a white light
`is produced. These
`I
`o colors afford an excellent example of comple-
`_' entary colors when used with artificial
`light.
`In
`daylight the ethyl violet screen appears deep blue in
`color, instead of appearing purple as it does .in the
`light
`from a tungsten incandescent
`lamp. Other
`transparent media for further demonstrating these
`5_ ethods are readily selected from the many organic
`idyes available. Uranin, fluorescein, carmine, patent
`Lblue, and filter blue-green are satisfactory.
`'
`In Fig. 24 the construction of an erratic color-
`Lmixing disk is illustrated. To a disk of stiff card-
`llboard a sectored disk of cardboard is rigidly fastened
`.by means of a circular rivet. The latter disk has
`*,two
`60'’ openings, as
`shown in :51. Another disk,
`E-arranged concentric with the other disks and between
`-"them,
`is permitted to slip at will about the rivet as-
`,_an axis.
`If the latter disk is prepared as shown in
`
` lI
`
`|
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`COLOR AND ITS APPLICATIONS
`
`64:
`
`'
`
`
`
`12 many striking colors are obtained on rotating
`combination.
`Fig. 25 illustrates a simple arrangement for col:
`mixing. The wheel is similar to that employed in :2
`Simmance-Abady flicker photometer.
`The periphai
`
`
`
`‘C ’%"""“
`Q
`'*~
`
`Fig. 24. —A.n erratic color-mixing disk.
`
`this wheel consists of truncated cones poin-ti.
`of
`in opposite directions.
`The
`axes of
`the
`co-€33
`are eccentrically placed at equal distances on ei -.3
`side of
`the axis of
`the wheel and parallel
`to ii;
`In the angular position shown in the illustrati
`5
`S
`
`
`
`to
`
`Fig. 25.——A simple color-mixer.
`
`
`
`the eye, looking at the wheel in a direction at
`angles to the axis, sees one conical surface illu -51..
`nated by one light, L, and the other by the other lig._
`L’.
`Colored screens, SS, are interposed betwe
`the wheel and the fight sources. By having the lam
`movable on a track any combination of brightness
`
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`
`
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`igte glass and 00 are
`
`65
`COLOR-MIXTURE
`
`
`’?i;_y rotating the wheel rapidly. Pigments may also
`we applied directly to the wheel.
`In Fig. 26 is illustrated
`gnother simple instrument
`or mixing the colors from
`éither opaque or
`trans-
`‘arent media. A wooden
`"ex is
`constructed
`as
`_'_own and painted black
`_"' ide. G is a transparent
`
`‘in of the two colors can Fis- 96-—A simple color-mixer for
`-."
`transparent or opaque media.
`
`‘id 00 are
`
`removed,
`
`the
`
`/
`
`/
`
`/
`
`are
`colored objects
`placed at PP, and the
`lamp is moved to and
`fro as before. The
`
`range of mixtures in
`the last case is not
`
`/
`
`/
`
`/
`
`/ \
`
`\\
`
`\
`
`infinite as in the case
`of transparent media;
`however, modifica-
`tions can readily be
`\
`'\\C
`made
`so that
`
` the
`range
`is
`Fig. 27. — La.mbert’s color-mixer.
`extended.
`
`A simple experiment devised by Lambert, though
`
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`
`is of interest owing to its extreme simplicity.
`illustrated in Fig. 27. G is a plate glass and C 9
`colored objects. The colors are mixed one by
`flection,
`the other by transmission. By turning‘
`glass and shifting the eye the proportions c '
`altered considerably.
`An apparatus of considerable use is a booth 5
`taining red, green, and blue incandescent lamps -.3;
`trolled by rheostats.
`If the colors are carefully .1;
`many interesting experiments can be performed, ..
`cluding the effect of quality or spectral charact_
`light upon colored objects (# 67).
`Many instructive experiments can be prod
`by the use of shadows cast by colored fights.
`0'5"
`especial interest is
`in Fig. 28, because it
`sents the additive p '-'_
`ries, their complement I-".3
`(the subtractive prim
`and White light prod =5.
`by the sum of the
`primary colors, — -_
`green, and blue.
`
`Fig. 28.—A shadow demonstration of difiusing blotting
`the additive and subtractive methods Sfifiened by a board ii‘;
`of color-mixture.
`_
`erected three planes
`white diffusing material about eight inches in he‘
`The latter meet at
`the center of
`the circle-=
`angles of 120 degrees with each other. At p0_
`several feet away, along the three arrows, red,
`and blue fights are placed somewhat above the 5.?
`of
`the circle. These should be small sources
`“quite powerful, concentrated tungsten filament :-=.-
`being quite
`satisfactory. The experiment
`is
`-F7-'
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`VIZIO 1016
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`COLOR AND ITS APPLICATIONS
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`In__
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`

`
`
`
`'
`
`COLOR-M'IXTURE
`
`It will be
`geen if the plane of the circle is vertical.
`.5'een that
`the nearly rhombic areas on the circle
`indicated by R, G, and B each receive light from only
`ne source. These areas will then appear respectively
`._,-ad, green, and blue. The areas on the opposite
`':"'des of the circle, BG, P, and I’, each receive light
`I_ am only two sources. They appear in colors com-
`._'1'j1e-mentary to the above primaries. They also rep-
`resent the subtractive primaries and the colors which
`qemain after
`red, green and blue are subtracted
`espectively from three white lights. The remaining-
`"_ eas of
`the circle marked W represent the regions
`Iivhich receive light from each of
`the three sources,
`with the result that if the colors and intensities of
`
`the light sources are correct, and if the sources are
`-sufliciently distant
`in comparison with the size of
`i'_t'he circle, these areas appear a uniform white. This
`“experiment is simple and is very satisfactory for dem-
`pnstration before large audiences. The lights should
`e controlled by separate switches and rheostats.
`A rotating disk can be readily colored, so that it
`pvill appear, when viewed through a radial slit placed
`“close to it, a fair approximation to the spectrum. The
`mixing of the colors by rotation obviates the neces-
`sity of
`the great care in blending colors in painting
`a spectrum that
`is to be viewed when stationary.
`=.'I‘he colors will not be of spectral purity, owing to
`the -limitations of the pigments, but the disk will be
`structive and affords a ready means of producing
`p spectrum for reproduction by color photography.
`an approximation to the prismatic spectrum can be
`readily produced as shown in Fig. 29. The approxi-
`._'_mation can be made as close as desired by touching
`‘up various points with pigments where necessary
`--or by varying the geometric figures.
`If a circle be cir-
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`COLOR AND ITS APPLICATIONS
`
`
`
`cumscribed about the inner square and a square
`turn be circumscribed about
`this, circle, and so .,_,
`until four circles -
`'
`
`I
`
`- \-"
`-
`,...11l||lliill!!!!!Il||
`
`,
`_
`_
`Fig. 29.—l2|lustratuig a disk for appronma-
`ting a prismatic spectrum.
`
`four squares are pr_
`
`ing hollow squares
`painted red, yello
`green, and violet -.;g
`spectively and the r_'
`mainder of the on :-.'-'
`
`
`
`circle be painted bla
`_
`,
`_
`3-
`fa“:
`approx-1313-t1-‘"
`to a prismatic sp 5:
`trum is obtained. The same results can be pr
`G .9-0
`D-Ci ('3 I'D D- 3E-*- sO3 e3"!‘s«2 3.F3‘ 9|:‘< s3 I'D
`——red, green,
`and blue.
`If
`the
`spectrum =3
`duced by rotation is not satisfactory at all‘ points,-j
`can be readily made so by the judicious use *
`pigments, or, as already stated, by altering the go,
`metric figures.
`The more simple methods of mixing colors
`been described in this chapter; however, it will
`borne in mind that many of
`the instruments
`methods considered in succeeding chapters are -i
`rectly or indirectly applicable to color-mixture.
`
`
`
`
`
`=5
`
`REFERENCES
`
`Captain W. de W. Abney, Colour Measurements and M‘
`London, 1891.
`‘
`O. N. Rood, Colour, 1904.
`Chevreul, Harmony and Contrast of Colours, 1839.
`
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