often be valuable, it is quite possible to produce them. The effect of a drawing in lead-pencil may be imitated by using graphite as the pigment; red chalk may be imitated by Venetian red; for sepia and bistre effects these pigments themselves may be used.
For most purposes, however, a fine black, either neutral, or inclining in tone to brown or purple, will be preferred. Fine lampblack, or good Indian-ink, will, in such case, generally form the basis of the coloring matter. If the color required be a pure neutral black, the addition of a blue pigment is necessary to neutralize the brown tint of Indian-ink; and, where necessary, coldness is corrected by the addition of some warm color. The selection of this color will be governed by the tint desired, and by the considerations of permanency. Many of the most beautiful tints are most fugitive. Carmine, for instance, is unstable; and some samples are injured by the action of the chromic salt. Crimson lake is a valuable color, but it is not strictly permanent. Indian red is a very powerful and very-permanent color. Venetian red is also permanent. For blue, ultra-marine is quite satisfactory as regards permanence.
In judging of colors for this purpose, it should be borne in mind, that the actual effect of color employed is chiefly seen in middle tint. It is difficult to distinguish much difference between a blue-black, a brown-black, a purple-black, a rosy-black, etc, in the extreme darks of a picture; but the tone is easily distinguished in middle tint, and, as, a rule, warm half-tones are the most pleasing. It should also be remembered that a weak picture will often look brilliant in a warm tone, whilst a vigorous print will look feeble in a cold color.
We have stated before, that by the addition of a large proportion of color to the gelatine, a vigorous print may be obtained from a feeble negative, and by the use of a
