In watercolor you are working only with transparent paints. The white or tinted ground shows through all the painting. If you want to hide it with an opaque color, then give up watercolor altogether. If your painting has the effect of one done in opaque paint, however cool and clear the color may be, the spontaneous, fleeting and watery character, the tenderness of its nature would be lost. Opaque paint or paint too much overlaid produces "holes" in the picture, particularly if in other places there is no more than a single layer of paint.
You know by now, of course, that white should never be found among watercolor pigments. White should be created only by untouched paper, at most gone over with a clean brushful of water. If a patch of color is too dark it can be moistened with a clean brush and some of the paint removed. Naturally, the paper will never be quite white again where paint has once been on it.
The nature of, the paint allows the following method to be tried: let a first draft in not-too-heavy paint dry completely and then lay the whole sheet of paper in water. As soon as the colors are dissolved, rinse it. This must be done quickly and thoroughly to prevent the runny paint from sticking in new places where it is not wanted. The paper is then dabbed dry with a series of clean cloths; this removes still more paint. A very faint image will remain, its strength depending on the kind of paper and the paints. If the pigment is colloidal in fineness, more will stay in the paper than if the coarser pigment powder was used. Differences in the granulation will thus affect the depth of color left by the different paints. You can then paint further on the paper while it is still damp or has been dampened again.
This method gives you a sure foundation for a carefully thought out, detailed composition; but, of course, it loses the rapid, unfinished charm of a spontaneous painting and, as has been explained, the pure white of the paper.
Another method gives a similar effect: you work over the whole picture with very weak colors and put in deep, full colors only when you are certain of everything else. The final effect is more brilliant and harder than with the washing-out method, because some places on the paper can be left untouched.
At first every watercolorist tends to make a number of technical mistakes due to a lack of sureness in putting down form and color. One of these mistakes, or faults, is working too slowly. If the paper dries too much, the paints, particularly the very fluid ones, dry with a dark rim round them which is very hard to take out, even by washing over w\th water. It would be wrong to give up using liquid paint because of this, as the animation of the work would be lost and the temperamental effect of the picture with it.
If you want to begin more gently, more tentatively, then start with cool, light colors. This is done for a tentative beginning in any technique. The natural model provides a parallel: the distance is always cooler in color than the foreground and tends to blue. Warm, close colors come last. If you paint with the reverse procedure, the picture becomes heavy and without contrasts, which is especially unfortunate in a watercolor. Every picture should be built up from weak to strong colors, not vice versa. In watercolor painting this means omitting the strongly colored areas until the cool, duller colors and weak s'hadow tones can be seen.
When discussing pigments we mentioned that black has its place in watercolor, if it is transparent. Otherwise it would be an alien element among the colors. Black should always either stand alone or under a color. If transparent black is laid over other colors it kills them completely and makes them colorless and dirty, but as an underlay it can, particularly in a very thin gray application, give the illusion of substance and solidity.
The limits of depth are reached in watercolor when the application of a dark color begins to be opaque. It may be that you sometimes put on a light yellow or green or blue so that it is almost opaque, but if the color becomes darker it is permissible only if it lets through a shimmer of the color of the paper. An impression of great depth can be achieved- in water color even with very light colors. Like a drawn sketch, the watercolor which most stimulates the beholder to co-operation arouses his imagination and thus can affect him more than an oil painting. The oil painting has to formulate more unambiguously with its depth of color and the technical manner of reproducing exact detail, or else be consciously indistinct. The fortuitous does not suit it.
Illusion or suggestion, inviting the collaboration of the beholder, is the essence of the watercolor as an art form. For instance, the illusion of twilight and darkness can be obtained not only from depth
of color but from tone: you can paint a twilight scene in the lightest colors if the characteristic color harmony, the dominant tone of the hour, is rightly caught. This matters more than depth.
I said, earlier, that watercolor is composed of "pure" applications of color. This does not mean that you must, for instance, make green by putting pure yellow and pure blue onto the paper. By "pure" is meant clear and definite mixtures made on the palette. (In no painting is it permissible to mix paints on the picture itself.) Correction of a color can be done only by overpainting with a transparent wash or, if that cannot help, by washing out the wrong color with water.
Overpainting requires great speed so that the color underneath does not smudge. It cannot be done while the paint is too wet. A feeling for the correct moisture of the paper is a matter of experience and ultimately, too, of personal taste. Some artists produce their best effects with absolutely liquid colors which even run into each other; others can work only if the paints dry clear, without a rim, next to each other.
Every painter has his preferred technique, but there are some effects which can be expressed only in watercolors: cool light, misty springtime, soft autumn, and, ever and again, water-rain, streams, lakes, melting snow. It seems that anything that is wet calls for a technique that uses water profusely as its elixir.
You can see how difficult watercolor painting is. Even if you prefer painting in oils and find yourself more at home as a beginner seeking out the tight coloration by trial and error with oil paints, watercolors are still the best teacher and ultimately the best criterion of ability, for you have to define your form and color at the first stroke, practice speed and concentration and work broadly and simply. Thus it is quite right that watercolors are used almost exclusively in the schools, although a good painting is so difficult. It is, besides being the simplest technique, of the highest educational value.
Watercolor is the beginning and the crown of all painting technique.