Colorimetry

“ Experiment shows that all the various hues of the spectrum, as well as all (including white) that can be formed from their mixture, may be derived from no more than three distinct colours. There are, in fact, an indefinite number of triads of colours which, in suitable combinations, are capable of producing the sensation of every tone, tint, and shade of colour which the eye of man has ever beheld.
Old-fashioned books, such as an early edition of Ganot’s “Physics,” tell us that the three “primary” colours are red, yellow, and blue, and that all others are produced by mixtures of these. ”

“ The Three Primitive Colours, by the endless varieties of their solvents, regulate, more or less, the whole economy of a picture; and the abundant stores of nature are faithfully imitated by their agency. Thus, the Primitives being red, blue, and yellow, the colours produced by their combination are purple, orange, and green; these, in their turn, may be extended to every tint that exists. The junction of the Three Primitives absorb all, and form neutral tint, which, by the addition of quantity, produces black. ”

“ White may be produced by two simple colors alone, as by red and green; more generally, if we isolate three suitably chosen colors in the spectrum, such as particular shades of red, green, and violet, we may, by mixing them in different proportions, imitate the impressions produced by all the colors. Artificial colors, formed, for example, of rays selected from the spectrum, may be simple or compound, without the eye being informed of the difference, except, perhaps, when they have a shade of purple or of rose, for we know then that those colors do not exist in a simple state. ”

“ As an artist's color, it replaces almost all the other red pigments which we have inherited from the past. The same chemists have an equally powerful yellow and blue under careful observation, and it is highly probable that in another year or two these, also, will be given to the world. Now it is evident that if painters can secure these three primary colors in two values, a light and a dark shade, they will, with the addition of white and black, have a perfect palette ”

“ The vermilion shade of red is approximated by mixing white with orange-red.
The colored crayons with which the layout man should be supplied are exceedingly useful in determining color combinations. The eye is a reliable guide in this matter, if it is carefully trained to recognize color harmonies. It should be easy to distinguish the right from the wrong color treatment in Examples 5 and 6. The colder color should always predominate; backgrounds of bright red and bright yellow are difficult to harmonize with any color of ink excepting black. ”

“ We are all familiar with the fact that there are three primary colours, and we are naturally led to consider these in the light of the experiments just made. As good a definition as any other of a primary colour is that it is a colour which cannot be formed by the mixture of any two or more25 colours. The original investigators in colour phenomena were the artists, and they found that neither red, nor yellow, nor blue could be formed by any mixture of pigments on their palette, but that all other colours could be made by a mixture of two or more of these three. ”

“ In pigments these effects are imitated by the mixture of white with a color to produce tints, and black for shades, or more generally instead of black some dark natural pigment approaching the hue of the color, may be preferred because a black pigment will too often impart an unexpected and undesirable hue to the color. As for example, in making shades of red some natural brown pigment is better than black, and so various dark browns and grays are used for different colors. ”

“ If more than two color disks, besides white and black, are used they will neutralize each other more or less, and a neutral gray or a gray and some spectrum color will be the result. For example, if yellow and blue in nearly equal parts are introduced in connection with red and orange, the yellow and blue being nearly complimentary to each other will produce practically a neutral gray, and the result will be the same as if only red, orange, white and black were used. ”

“ When the eye has been fatigued by looking intently for a few seconds at a red spot on a white wall and is then slightly turned to the wall, a faint tint of a bluish green is seen, and this is called the accidental color of the red, and is supposed to be identical with its complementary color. If with the disks we determine a color which with a given color will produce by rotation a neutral gray, we have the complementary color more accurately than by any other means at present known in the use of pigmentary colors. ”

“ It is important that the words which we use for the different colors should be well understood, that in using them we use them with the same meanings. By Red I mean the only positive color which shows no element either of Yellow or of Blue. It is the color which we often describe by the word crimson, and we produce it by the mixture of Rose Madder and Vermilion. By Yellow I mean the only positive color which shows no element either of Red or Blue. It is the color of the primrose which may be produced by the pigment Aureolin. ”

“ This is because it is what the geneticist calls a recessive character. A man may have a color-blind father and still not transmit the defect. But a color-blind woman, married to a color-blinded man, transmits the defect to all off-springs, both sons and daughters.
ALTERING COLOR To brighten color, add yellow; to give it warmth, add red. To brighten and warm, add orange. To deepen and cool, add blue. To cool and lighten, add green; to deepen and warm, add purple.
Ultramarine blue contains sulphur and will tarnish with admixtures of pigment containing lead. Substitute zinc white. ”

“ Combined with the primary blue, yellow furnishes all the variety of the secondary green, as well as, subordinately, the tertiaries russet and olive. It also enters in a [82] very subdued degree into cool, semi-neutral, and broken colours, and assists in minor proportion with blue and red in the composition of black.
As a pigment, yellow is a tender delicate colour, easily defiled, when pure, by other colours. In painting it diminishes the power of the eye by its action in a strong light, at the same time becoming less distinct as a colour ”

“ If in an attempt to match a color which seems to be a broken blue, something else besides the blue, white and black is required, it must be either green or violet, i.e., one of the two standard colors adjacent to the blue in the spectrum. In other words, every color in nature is a spectrum color, i.e., either a pure spectrum color, a tint or a shade of a spectrum color, or a broken spectrum color. ”

“ To determine the hue of a pigment from the analysis of the light it reflects is a problem in physiological optics, the solution of which varies with the character of the observer's eye. The three primary color-curves of the eye must be determined, and the total intensity of each wave-length of the spectrum of the pigment must be divided in the proportions indicated by the color-curves into three components—red, green, and violet. ”

“ We mix the red and the green lights together, and find that the best mixture is always paler than the orange, but by adding a small quantity of white to the orange we at once form a match. In the same way if we have a greenish-blue to match, we shall find that we can only make the match when we add a little white to the simple colour. Now let us shift the position of the slit in the green just a little—a very little—towards the blue, and again try to match orange. Do what we will we cannot find apertures to the slits which will give us the colour, though it be diluted with white. ”

“ One must remember always in studying color that we are treating with the material, not with the illusion. We are dealing with pigments, not with prismatic phenomena, and it must be obvious that the only three primary colors that can be used in a way to produce all other colors are red, yellow and blue. ”

“ White, which is also a cold color when added to black makes a cold gray. Yellow added to red forms a warm orange.
MEANING OF COLORS White is said to mean purity; blue, fidelity or truth; red, love or sacrifice; green, envy; pink, modesty; violet, innocence; yellow, jealousy; black, sorrow or distress, and lavender, passion.
4 ART OF COLOR MIXING Mixing colors is an art in itself. With a combination of the chief colors—red, yellow, blue (and black and white) , thousands of shades and hues may be produced. ”

“ To produce pure and permanent compound hues requires practice and knowledge, and we too often see in the works of painters combinations neither pleasing nor stable. Colours are associated with each other which do not mix kindly, and compounds formed of which one or both constituents are fugitive. As a consequence, mixed tints are frequently wanting in clearness, and, where they do not disappear altogether, resolve themselves into some primary colour; orange becoming red by a fading of the yellow, green yellow by a fading of the blue, and purple blue by a fading of the red. ”

“ It will probably happen that a good deal more of one of the pairs of the colours is required in the disc than of the other, and supposing that the two are each used of the full brightness which the pigments are capable of giving, it follows that in a diagram where equal areas are filled with the pigments as complementary, some means must be adopted to give the true depth of tone to each. The mixture of white will heighten the luminosity of either, or the admixture of black will lower it, but often alters the hue. ”

“ The best-known examples of colour analogy are, of course, the greys, and colour effects are produced by dark grey used along with mid grey, or mid grey employed with light grey and so on. At the upper end of the series the light grey can be graduated into white, whilst at the lower end the dark greys can be graduated into black. These colour combinations are always in favour, and no matter what the prevailing shade may be there is always a certain proportion of trade done in the neutral tints. ”

“ As every compound colour must be a mixture of the same two colours in certain proportions, it follows that the green colour-blind person can match every compound colour with some one ray of the spectrum, and that every colour must to him be either red or violet, diluted with different proportions of white light. ”

“ More than one professional artist has already worked successfully from nature in oil colors with a palette consisting of only close approximations to the six standard colors with white and a few grays. A person whose color perception has been trained by the use of the color disk in six standard colors with [Pg 121] colored papers to correspond, will undoubtedly be able to more truthfully reproduce the colors which he sees in nature, on the canvas or paper by means of such a pallette than if he had been taught by any other system and used the ordinary pigments. ”

“ All spectrum colors are pure, while no pigmentary color is absolutely pure, but the pigmentary color which approaches most nearly to the corresponding color in the spectrum must be selected as the pigmentary type of purity of that color. For example, the standard for green must be the best possible pigmentary imitation of the spot in the spectrum which by general consent is called green, and so not only for the six standards but for all their combinations which produce the other colors in nature. ”

“ Colour Contrast.—Most foremen have a fairly good idea of the methods of using colours in articles where the scheme is mono-chromatic or one-coloured, but when it is a matter of blending colours which are entirely different in character and hue the difficulties begin. The most usual faults are combining colours which can never harmonize so as to give results agreeable to the aesthetic sense; colours are combined which vary greatly in relative depth of hue, that is, light, delicate shades are employed indiscriminately with colours which are strong and decided in nature. ”

“ Thus the secondaries, if they are not already of the colour required, may be brightened or subdued, deepened or paled, with comparative impunity. The artist who, from long years of experience, knows exactly the properties and capabilities of the colours he employs, may in a measure dispense with secondary pigments, and obtain from the primaries mixed tints at once stable, beautiful, and pure; but even he must sometimes resort to them, as when a green like emerald or viridian is required, which no mixture of blue and yellow will afford. ”

“ With such it is a taste acquired from the study of old pictures; but in nature hardly any object above ground is black, or in daylight is rendered neutral thereby. Black, therefore, should be reserved for a local colour, or employed only in the under-painting properly called grounding and dead colouring. As a local colour, black has the effect of connecting or amassing surrounding objects, and is the most retiring of all colours, a property which it communicates to other colours in mixture. ”

“ As the retina retains these two impressions together, they produce the impression of purple.
Fig. 40.—Disc painted Blue and Red.
For experiments in colour this duration of impressions is of great value, for we can take advantage of it to compound the colours of pigments together in a very simple manner. For instance, we can take a circular disc painted in sectors with blue and red (Fig. 40) , and produce a purple by causing it to rotate round its centre. ”