THE AEROGRAPH OR AIR "BRUSH." This is an apparatus for spraying fluid colours on to any surface, by which a beautifully stippled effect can be produced with a minimum of trouble. Fig. 465 shows sketch, just to see how it will come. Now sketch in lightly, on the paper, the posi tion of the different objects with the chalk point ; of course, using chalks of a kind to match the paper. It is more frequently bromides which are so treated, negative processes seldom being done in this way, so that black chalks will be mostly needed. The paper should not have a smooth sur face. The best effects arc obtained on crayon papers. If the paper is smooth it will be necessary to rub it well all over, first of all, with cuttlefish powder on a tuft of wool, to give it a tooth to hold the powder ; but bear in mind that this must be done very lightly, or the effect afterwards will be scratchy. The background is then stumped in, using the paper stumps for the details, and the wool, leather pad, or finger tip for the broad shadows, according to taste. A very nice grain, in the deepest shadows, can he obtained with the finger tip on such a surface, and the lighter parts may be afterwards wiped out with the the instrmnent at work, while a detailed illustration of the fountain part, which is held in the hand, is given in Fig. 466. The apparatus is worked by compressed air from the reservoir, supplied by a kind of air-pump with a. piston action (see Fig. 467). The reservoir is kept filled by an occasional motion of the foot, and the colour is driven out in an exceedingly fine spray. The depth of tint is governed by the length of time the brush is held opposite the part treated, and the breadth of tint by the distance from it. The farther
the brush is away, the more the spray spreeds, and rice re rso . The pigment, which may be of any colour, is placed in the brush reservoir R (Fig. 466). using for this purpose a small camel-hair mop. A few motions of the foot pumps sufficient air into the air reservoir to last for some minutes. The amount of air in the reservoir is indicated by a glass gauge, which may be fixed by the side of the easel. In Fig. 465 the gauge will be noticed hanging over the top of the largement, and connected by a tube to Lhe air reservoir. As soon as the gauge gives warning that the air is becoming hausted, the foot pump is again set in motion. The air enters the brush through the tube connection at A (Fig. 466), and is released by a 'downward" preSsure on the button B, which also controls- the amount of air, and consequently colour, emitted by a backward or forward move ment. The colour is driven the opening in the nozzle, e. The ring s may be used to limit the forward motion of the button or lever, thus regulating the width of the line if desired. The instru ment - is admirably suited for coloured work, and it ' is an advantage that the surface of the picture requires no prepara tion. Fig. 468 shows the manner in which the colour is-distributed. • The apparatus is easy to manipulate, and gives charming re sults. Its purposes must not be misunder stood, however. It requires the same artistic skill in the arrangement of tones, etc., and its success depends as•much on the expertness of the user, as with any other brush.