As I have stated above under “Varnish,” every degree of consistency of the varnish requires a definite quantity of color. If one adds too little color, the paste will be too soft for bromoil printing, and cannot be spread. Too much color is hardly possible with the stiffest consistency; the limit lies when the color no longer dissolves in the varnish. Too little, on the other hand, results in the ink smearing on the print. It is, therefore, absolutely necessary in using very thick varnish to absolutely saturate it with color. Not going far enough in this direction, or the omission of the preliminary warming of the varnish, are the only sources of failure. In working with varnish of lighter consistency, it will be necessary to stop the addition of color as soon as the slaty gloss appears.
If the grinding of the ink were to require as long as it takes to read this description, the waste of time would be considerable. Actually the whole work may be carried out in two or three minutes if one uses the methods suggested, and after a little experience is gained, which soon comes after a few trials. Long before the water for the bromoil print is hot, the ink will be ready.
Ink Mixing.—As it is not always possible to use existing colors, and it is necessary in many cases to alter the shades for artistic effects, the basic colors must be diluted with other colors. This can be effected in many ways, best by adding another color to the predominant color powder during the mixing. Bone black is specially valuable for this purpose. This is by itself an unpleasant color, for it is a discordant brown-black which can hardly be used alone. If other colors, however, are added to this bone black it produces beautiful tones. Thus, for instance, the addition of a minimum of blue (indigo or ultramarine) gives a deep, velvety black; if a little more blue is added, we obtain a beautiful blue-black. A little bone black mixed with burnt umber gives a fine warm black, and so on.
The tone of crayon sauce is especially beautiful, if it is used without the addition of any other color, and especially that quality obtainable under the name of Sauce Velours is particularly excellent.
Another kind of color mixture is that in which black is taken as the fundamental color (which is desirable when it is not desired to mix up ink for each print) and then instead of diluting the stiff ink with linseed oil or other diluent, an ordinary good copper-plate ink or even ordinary oil colors are used. By this method of working I can shade and soften in one operation, and it is highly advisable to use it when it is desired to obtain different tints easily. The method of mixing is very important and I will therefore give some examples. If to the stiff black ink (bone black), I add a little indigo oil color, I have at once a deep black; the addition of vandyke brown or burnt umber gives a magnificent brown; a fine dark green is obtained with light cadmium; this dark green becomes blue-green when I add a little indigo. An admixture of caput mortuum shows violet tones; red tube colors, such as Indian or Pompeian red, ochre, etc., give various reddish brown nuances. These additions can be varied in manifold ways, dependent only on what tube colors are at hand. It is strictly necessary, however, that only the least possible quantity of tube color should be added, about as much as the head of a good-sized pin, to keep the ink from becoming too soft and going beyond the desired tint. When a suitable shade has been attained, all further dilution must be effected with linseed oil, petroleum, etc. When I specially recommended the Mussini or Fiedler colors, it was because they are prepared with resin oils and are therefore specially suitable for our purpose. But all other good oil colors can be used. When I write briefly only oil colors, I mean obviously artists’ oil colors, and not others which may be used for other purposes than for artistic painting.
Finally the black may be diluted with linseed oil to the usable consistency of hard ink and also diluted on another part of the palette with oil color or copper-plate ink of another shade to the consistency of a soft ink, and then both colors may be mixed either on the print or in the brush.
Very fine gradations may also be produced as follows: the bromoil print is pigmented as usual to obtain as clear shadows and clean high lights as possible, with not too high a relief. When the print is completely finished, it should be placed in a 2 per cent cold solution of ammonia, this allowed to act for two minutes and then rinsed for one minute in clean water. Then the print, which is considerably swollen, should be very carefully dried off, so that no ink comes off on the cloth, and the latter leaves no imprint of its structure. Now the whole print is gone over with a clean brush, on which is a very little pure oil color. By thus using light, transparent (lasur) colors, and only such ought to be used for this purpose, the print may be given an extremely delicate film of ink, through which the first image shines with full vigor. This gives an effect similar to that which the gum printer obtains by multiple printing.
According to whether the whole or only parts of the print are gone over with the “lasur” color, the most varied effects are obtained, such as deepening of the shadows, or lowering of the high lights, or both.
It is naturally impossible to describe this process exactly in print. Much must be left to artistic feeling, without which hair-raising color discords will probably be produced. Still, in order to give the beginner some starting point, it may be mentioned that black, brown or red tones may be easily treated with inks shaded towards grey, blue with pure grey, and so on.
The following summary of color mixtures for the beginner is also given: red-brown is obtained by mixing bone black, Indian red, and possibly dark alizarin lake; violet results from bone black with red and blue; dark green, from black, cadmium and blue; brownish-green, from black and indigo; bright green, from a little black with cadmium and indigo; red chalk, from black, brown and Indian red.