Armengaud, Jacques Eugène; Leblanc, César Nicolas   [Hrsg.]; Armengaud, Jacques Eugène   [Hrsg.]; Armengaud, Charles   [Hrsg.]
The engineer and machinist's drawing-book: a complete course of instruction for the practical engineer: comprising linear drawing - projections - eccentric curves - the various forms of gearing - reciprocating machinery - sketching and drawing from the machine - projection of shadows - tinting and colouring - and perspective. Illustrated by numerous engravings on wood and steel. Including select details, and complete machines. Forming a progressive series of lessons in drawing, and examples of approved construction — Glasgow, 1855

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MANIPULATION OF SHADING- AND SHADOWS.

87

Again, let us suppose the half-plan of the cylinder,
f m' cl' c, Fig. 5, to be divided into any number of equal
parts. Indicate these divisions upon the surface of the
cylinder by faint pencil lines, and begin the shading by
laying a tint over all that part of the cylinder in the shade
a c db, Fig. 6. This will at once render evident the
light and dark parts of the cylinder. When this is dry,
put on a second tint covering the line, a b, of separation
of light and shade, and extending over one division, as
shown in Fig. 7. A third tint should be spread over this
division, and one on each side of it, as in Fig. 8. Proceed
in this way until the whole of that part of the cylinder
which is in the shade is covered. The successive stages
of this process may be seen in Figs. 9, 10, and 11.

Treat in a similar manner the part, feig, and com-
plete the operation by covering the whole surface of the
cylinder—excepting only the division, e m n i, Fig. 12
—with a very light tint; the cylinder will then assume
the appearance presented by Fig. 12.

Shading by softened tints.—The great advantage which
this method possesses over the one just described, consists
in imparting to the shade a much softer appearance; the
limitations of the different tints being imperceptible. On
the other hand, it is considerably more difficult, requiring
longer practice, and greater mastery over the movements
of the brush, to accomplish it with tolerable precision.

Let it be proposed to shade by this method the segment
of the hexagonal pyramid, Fig. 20, PI. 56.

The plan of this figure is similar to that of the prism,
Fig. 4. Its position in reference to the light is also the
same. Thus the face, abed, should receive a uniform
flat tint. If, however, it be desired to adhere rigorously
to the preceding rules, the tint may be slightly deepened
as it approaches the top of the pyramid, seeing that the
surface is not quite parallel to the vertical plane.

The face, b g h c, being inclined and in the shade,
should receive a dark tint. The darkest part of this tint
is where it meets the line 6 c, and gradually becomes
lighter as it approaches the line g h. To produce this
effect, apply a narrow strip of tint to the side, b c, Fig. 18,
and then, qualifying the tint in the brush with a little
water, join another strip to this, and finally, by means of
another brush moistened with water, soften off this second
strip towards the line, 1, 1, which may be taken as the
limit of the first tint. This is shown in Fim 18.

O

When the first tint is dry, cover it with a second, which
must be similarly treated, and should extend beyond the
first up to the line 2, 2, Fig. 19. Proceed in this manner
with other tints, until the whole face b g he, is shaded,
as presented in Fig. 20.

In the same way, the face, e a d f, is to be covered,
though with a considerably lighter tint, for the rays of
light happen to fall upon it almost perpendicularly.

It may be observed that, consistently to carry out the
rules we have laid down, the tint on these two faces
should be slightly graduated from e a, to / d; and from
eh, to b g. But this exactitude may be disregarded
until some proficiency in shading has been acquired.

It is now proposed to shade the cylinder, Fig. 16, PL 56,
by means of softened tints.

The boundary of each tint being indicated in a manner
precisely similar to that shown by Fig. 5, the first strip of
tint must cover the line of extreme shade, a b, and then
be softened off on each side, as shown in Fig. 13. Other
and successively wider strips of tint are to follow, and
receive the same treatment as the one first put on. The
results of this process are shown in Figs. 14, 15, and 16.

As this method requires considerable practice before it
can be performed with much nicety, the learner need not
be discouraged at the failure of his first attempts, but
persevere in practising on simple figures of different sizes.

If, after shading a figure by the foregoing method, any
very apparent inequalities present themselves in the
shade, such defects may be remedied, in some measure, by
washing off redundancies of tint with the brush or a damp
sponge, and by supplying a little colour to those parts
which are too light.

Dexterity in shading figures by softened tints will be
facilitated in practising upon large surfaces ; this will be
the surest way of overcoming that timidity and hesitation
which usually accompany all first attempts, but which
must be laid aside before much proficiency in shading can
be acquired.

SECTION II.

Elaboration of Shading and Shadows.

In last section the simplest primary rules for shading
isolated objects have been laid down, and the easiest
methods of carrying them into operation explained. In
the present section it is proposed to exemplify these rules
upon more complex forms, to show where the shading may
be modified or exaggerated, to introduce additional rules
more especially adapted for mechanical colouring, and to
offer some observations and directions for effectively
shading the drawing of machines in their entirety.

Whatman's best rough-grained drawing-paper is better
adapted for receiving colour than any other. Of this
paper, the Double Elephant size is preferable, as it pos-
sesses a peculiar consistency and grain. A larger paper
is seldom required, and when the drawing to be made
happens to be small, a portion of a Double Elephant
sheet should be used.

The paper for a coloured drawing ought always to be
strained upon a board with glue or strong gum. Before
doing this care must be taken to damp the face of the
paper with a sponge well charged with water, in order to
remove any impurities from its surface, and as a necessary
preparation for the better reception of the colour. The
sponge should merely touch the paper lightly, and not
rub it. The whole of the surface is to be damped, that
the paper may be subjected to a uniform degree of expan-
sion, thereby insuring, as it dries, a uniform degree of
contraction. Submitted to this treatment, the sheet of
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