Were it possible to procure three pigments devoid of chemical affinities, and each of the same physical constitution, as of equal degrees of transparency or opacity, one truly representing the blue of light, another the red, and another the yellow, we should need no others, for of these we could form all other colours; but as no pigments come even near to the fulfilment of these conditions, we have to employ roundabout and clumsy methods of arriving at desired results.
There is one statement which I have made that, perhaps, needs a little elucidation, although the careful student may have seen the reason of my assertion. I said that purple harmonised with citrine, green with russet, and orange with olive. I might have expressed it (and many would have done so) thus:—The complement of citrine is purple, the complement of russet is green, and the complement of olive is orange. A colour which is complementary to any other is that which, with it, completes the presence of the three primary colours: thus green is the complement of red, and red of green, for each, together with the colour to which it is the complement, completes the presence of the three colours. But in order to a harmony, the complement must be made up in certain proportions. Let us now refer to our second diagrammatic table, and we there see that citrine is formed of two equivalents of yellow and only one equivalent of red and of blue. Now, in order to a harmony, each primary should be present in two equivalents, as one is present in this quantity—i.e., the yellow. One equivalent of blue and one of red (both of which are wanting in the citrine) form purple; hence purple is the complement of citrine, or the colour that with it produces a harmony. In russet one equivalent of blue and one of yellow are wanting, and these in combination are green—green, then, is the complement of russet. And in olive one equivalent of red and one of yellow are wanting—red and yellow form orange, hence orange is the complement of olive.
I have spoken of all colours as of full intensity and purity, but we have to deal also with other conditions. All colours may be darkened by black, when shades are produced; or reduced by white, when tints are produced. Besides these alterations in intensity, a portion of one colour may be added to another. Thus, if a small portion of blue be mingled with red, the red becomes a crimson or blue-red; or if a small portion of yellow be added to the red, the latter becomes a scarlet or yellow-red. In like manner, when yellow is in excess in a green, we have a yellow-green; or when blue is in excess, a blue-green; and so with the other colours. Such alterations produce hues of colour.
We now come to the subtleties of harmony. Thus, if we have a yellow-red or scarlet—a red with yellow in it—the green that will harmonise with it will be a blue-green; or if we have a blue-red or crimson—a red with blue in it—the green that will harmonise with it will be a yellow-green. This is obvious, for the following reasons:—Let us suppose a red represented by the equivalent number, five, with one part of blue added to it, thus causing it to be a blue-red or crimson. Were the red pure, there should be eleven parts of green as a complement to the five of red, of which green eight parts would be blue and three yellow; but the blue-red occurs in six parts, one of which is blue—there are, then, but seven parts of blue remaining in the equivalent quantity to combine with the three of yellow, one being already used; hence the green formed is a yellow-green, one of the equivalents of blue necessary to the formation of a true green being already in combination with the red, and thus absent from the green.
The same reasoning will apply to the scarlet-red and blue-green, and, indeed, to all similar cases; but to take the case of the crimson-red and yellow-green, as just given, and carry it a stage further, we might add two parts (out of the eight) of blue to the red, and make it more blue, and then form the complementary green of six parts of blue and three of yellow, and thus make it more yellow. Or we may go further still, and add to the red six of the eight parts of blue, when the admixture would appear as a red-purple rather than as a blue-red, in which case the complementary green—or, rather, green-yellow—would consist of two parts of blue and three of yellow. These facts are diagrammatically expressed in the following:—
In all these cases it will be seen that we have eight parts of blue, five of red, and three of yellow, only the mode of combination varies. This variation may occur to any extent, provided the totals of each be always the equivalent proportions.
These remarks will apply equally to hues of colour, shades, and tints, and to shades and tints of hues.
Care, and a little practice, will enable the learner to arrange colours into a number of degrees of depth, or shades, as they are generally called. (We do not here use the term as signifying pure colours darkened with black.) Ten shades of each colour differing obviously in degree of depth can readily be arranged by the experienced, the ten shades being equidistant from each other as regards depth—that is, shade 3 will be as much darker than shade 2 as shade 2 is darker than shade 1, and so on throughout the whole. Purple is a colour intermediate between blue and red. Imagine ten hues between the purple and the red, and ten more between the purple and the blue: thus we should have purple, then a slightly red purple, then a rather redder purple, then a purple still redder, and so on till we get purple-reds, and finally the pure red; and the same variations of hue at the blue side also. Imagine, further, the green having ten hues extending towards the blue, and ten more stretching towards the yellow; and the orange having ten hues towards the red, and ten towards the yellow—in all cases I count the colour from which we start as one of the ten, thus:—
