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

Seite: 93
DOI Seite: Zitierlink: i
http://digi.ub.uni-heidelberg.de/diglit/armengaud1855/0109
Lizenz: Creative Commons - Namensnennung - Weitergabe unter gleichen Bedingungen
0.5
1 cm
facsimile
MANIPULATION OF SHADING AND SHADOWS.

93

faint shadows of such objects, or, at best, machinery con-
structed of some unknown, light, and rather dirty mate-
rials.

The sectional surfaces of cast-iron are to be indicated
by one light tint of indigo.

The next most extensive and important component
used in the manufacture of machines is wrought-iron.
Precisely the same colours are to be employed to represent
this material as have been pointed out for cast-iron. The
difference in the appearance of these metals is produced
by altering the proportion of the two principal colours,—
Indian ink and indigo. These ingredients should be
mixed, and well mixed, in about equal proportions, a very
small quantity of crimson-lake being first rubbed in the
saucer. See Plate lxvi., Wrought-iron.

The same methods of shading and of laying on the
shadows prescribed for cast-iron are to be adopted in the
case of wrought-iron, keeping, however, all parts of the
latter lighter, particularly the body colour. The direct
and reflected lights must also present themselves more
distinctly, and to a much greater extent. Polished and
semi-polished surfaces invariably afford greater contrasts
of light and shade than other surfaces. The steps or rather
glidings from one extreme to the other are, moreover,
softer and more delicately graduated, and, therefore,
greater care is requisite in representing them on paper.
These remarks are very effectively illustrated by the frag-
ments of large screws shown on Plate lviii., and also by
the end view of the Locomotive-Wheel, Plate lx.

For the parts of wrought-iron in section a light tint of
Prussian-blue is most suitable. This is the only service
for which Prussian-blue can properly be made available
in colouring drawings of machinery. In conjunction with
Indian ink or indigo its inherent brightness entirely dis-
appears ; an ill-assorted union with the former producing
a dirty colour, in appearance not unlike that presented
by the surface of a stagnant pool; and with the latter
creating a tint bearing a striking resemblance to soiled
glass. For mechanical drawings, then, this colour must
never be used in combination.

Brass, except in small quantities, seldom makes its ap-
pearance in machinery. This is fortunate for the colourist,
as there is no metal more difficult to represent than brass.
The body tint is composed either of gamboge and burnt
siena, or gamboge and crimson - lake; the shading and
shadows being best expressed by burnt umber. See
Plate lxvi., Brass.

The most delicate and careful treatment is needed in
making use of these colours, for, when on the paper, they
are all of them very soft, and therefore highly sensitive
to every touch of the brush. For this reason the shadows
are best put on after the body colour, otherwise their
edges will inevitably present a smeary indefinite appear-
ance.

For representing brass and copper, the method of colour-
ing we have described in this section is particularly suit-
able. To attempt the production of a shade with burnt
umber, by means of a succession of tints, would merely

realize a complicated smear. We find, therefore, that the
shades and shadows of brass are usually represented by
Indian ink; but as gamboge almost invariably enters as
an ingredient into the body colour of brass, the result is
that the bright gamboge over the brown-black Indian
ink exhibits a species of green, to which we cannot find
anything comparable, but which commonly has a very
unpleasant effect to the eye.

In shading circular surfaces great management is re-
quisite. “Washing” is here entirely out of the question,
for even the necessary softening off with the brush is at-
tended with much difficulty. The brush should not pass
heavily or often over the shade tint, lest unseemly defi-
ciencies and streaks of colour present themselves here and
there, which prove rather difficult blemishes to repair.
The utmost care and experience, nevertheless, cannot
wholly insure the colourist against the perplexities of such
partial failures. The only way to manage these defects
is by delicate stippling; suiting the depth of tint to the
various degrees of shade affected, and then passing a soft
brush, filled moderately with dark body colour, very
lightly over the whole shade.

A light tint of gamboge is to be used for the sections
of brass.

The directions which we have given for the most ad-
vantageous treatment of the colours representing brass,
are equally applicable to those which exhibit the nearest
approach to copper, the colours to be used for this metal
opposing nearly an equal amount of difficulty in their
management. A mixture of orange chrome and lake, or
red-lead and lake, best represent this metal; its shades
and shadows being indicated by sepia, whilst its sectioning
is shown by a light tint of orange chrome. See Plate
lxvi., Copper.

Such are the colours, and such is the manner of treating
them, employed for depicting on paper each of the prin-
cipal metals used in machinery.

Having explained in detail the tinting of machinery in
reference both to its shading and body colour, we propose
to complete our remarks on mechanical colouring with a
few suggestions for imparting some peculiar effects to the
representations of masses of machinery.

We have already noticed that the shades and shadows
of a machine are modified in intensity as their distance
from the eye increases. Its body colour should be treated
in a similar manner, becoming lighter and less bright as
the parts of the machine which it covers recede from the
spectator.

When the large circular members of a machine have
been shaded, the shadows, and even the body colour on
those parts furthest removed from the eye, are to follow,
and the proportion of Indian ink in the tint used should
increase as the part to be coloured becomes more remote.
A little washing, moreover, of the most distant parts is
allowable, as it gives a pleasing appearance of atmospheric
remoteness, or depth, to the colour thus treated. Very
apposite cases of this kind occur in the plan and section

of Mill-Gearing, Plate lxix., on the casting within which

N
loading ...