The scumble may be used with the richer and darker colors, too, to modify towards richness the tone of parts of the picture, or to darken the value. Most often, however, its value lies in its use to bring harsher and sharper parts together, and to give the hazy effect when it is needed.
Scumbling will not have a good effect when it is not intended to varnish the picture afterwards; for the oil in the paint is absorbed immediately, and the rubbing of color gives a dead look to the canvas which is very unpleasant, and decidedly the reverse of artistic.
Glazing.—A very valuable process, the reverse of scumbling, is glazing. It has always been in use since the invention of the oil medium. All the Italian painters used it; it is an essential part of their system of coloring. The rich, deep color of Titian, the warm flesh of Raphael, and the jewel-like quality of the early German painters are impossible without some form of glaze. The Germans perhaps made glazes with white of egg before oil was used as a vehicle. But to glaze is the only way to get the fullest effect of the quality characteristic of the transparent paints.
A glaze is a thin wash of transparent color flowed over an under-painting to modify its tone or to add to its effect. It is not always transparent color, but usually it is. Sometimes opaque or semi-opaque color may be used, and it is a glaze by virtue of the fact that it is thinned with a vehicle either oil or varnish, and flowed on. A scumble is rubbed on, and is never pure transparent color.
Advantages of Glazing.—The advantages are the gain in harmony, in force, in brilliancy; you may correct a color when it is wrong, or perfect it when it is not possible to get the force or richness required without it. These are the qualities which have made it used by all schools more or less.
Disadvantages.—There are, however, quite as evident and marked disadvantages. The free use of oil as a thinning vehicle, although it makes possible a greater degree of richness of color, is very likely to turn the picture brown in time. Oil will always eventually have a browning effect on all paints, even when mixed with them as little as is absolutely necessary. If you make a tinted varnish of oil (which is practically what a glaze is), you add so much, to the surely darkening action of the oil on the picture.
If, again, you depend upon a glaze for the richness of color for your picture, and you use a color which is not permanent, your glaze fades, and your color is not there. A glaze is particularly liable to be injured by the cleaner if it ever gets into his hands. He works down to fresh color, and what with the browning of the glaze and the fact that the cleaner is more anxious that the picture should be cleaned than that its color should be fine, he will, in nine cases out of ten, clean off the glaze which may be the final and most expensive color the painter has put on it.
Glazing is little used nowadays, compared with what it once was. But there are times when you cannot get what you want in any other way, and when you are sure that glazing is the only thing which will give you your result, the only law for the painter comes in,—get your result.
Precautions.—If you do glaze, however, there is a right and a wrong way. You should not use a glaze as a last resort. It is better to calculate on it beforehand; for you always glaze with a darker tint upon a lighter one, so that if you have not allowed for this, you will get your picture too low in tone before you know it.
If you want to make your picture, or a part of it, brighter and lighter, bring it up in pitch with body color first, with solid painting, and then glaze it.