The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion; forming a complete course of mechanical, engineering, and architectural drawing by unknow

Author:unknow
Language: eng
Format: epub
Tags: Mechanical drawing
Publisher: Philadelphia, H. C. Baird
Published: 1871-03-25T05:00:00+00:00

BOOK OF INDUSTRIAL DESIGN.

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297, When two surface!' in the shade are uneqiuzlly inclined, umh reference to the, direction of the rays of light, the shadow cast by any object should he deeper upon that which receives it more direcily.

Thus, the shadow, a dfe, cast upon the face, f, of the prism, fig. [1, Plate XXVI., should be slightly stronger than that cast upon the face, g, because the first is more directly presented to the light than the second, as showTi by the lines, /' h' and /' c', fig. T.

These first principles are exemplified in the finished figures on Plate XXVI., XXVIL, and subsequent ones.

As, in order to produce the gradations of shades, it is important to have some knowledge of actual colouring or shading by means of the brush, we shall proceed to give a few short explanations of this matter.

Two methods of producing the graduated shades are in use— one consisting in laying on a succession of flat tints; the other, in softening off the shade by the manipulation of the brush.

We have already said two or three words about the laying on of flat tints, when treating of representing sections by distinguishing colours. (137.) These first precepts may serve as a basis for tJie first method of shading, which is the less diflScult of the two for beginners. In fact, according to it, the gi-aduated shade is produced by the simple superposition of a number of flat tints.

FLAT-TINTED SHADING,

298. Let it be required to shade a prism, A, Plate XVII., with flat tints:—

According to the position of this prism, with reference to the plane of projection, as seen in fig. 1, it appears that the face, a' h'-> is parallel to the vertical plane, and is fully illumined; it should, consequently, receive a clear uniform tint, spread over it by the brush, and made either from China ink or sepia, as has been done upon the rectangle, a, b, c, d, fig. A. When the surface to bo washed is of considerable extent, the paper should first be prepared by a very light wash, the full intensity required being arrived at by a second or third. (137.)

The face, b' g', being inclined to the vertical plane, and completely in the shade, should receive a tint (294) deepest at the edge, b c, and gradually less intense towards g h ; this is obtained by laying on several flat shades, each of different extent. For this purpose, and to proceed in a regular manner, we recommend the student to divide the face, b' g', fig. 1, into several equal parts, as in the points, 1', 2', and through these points to draw lines parallel to the sides, b c, g h, fig. A. These linos should be drawn very lightly indeed, in pencil, as they are merely for guides. A first greyish tint is then spread over the surface comprised botwocu tho first line, 1—1, and tho side, b c, as in fig. 2; when this is

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