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.

01

as if it were made of glass, it might look very light and
pretty, hut there is a reasonable probability that the brittle
nature of its apparent composition would produce an un-
pleasant thought of personal danger, and suggest the pre-
caution of remaining at a respectful distance from such an
engine, lest it should fly to pieces and do serious injury.

The parts of a machine being usually constructed with
mathematical accuracy, and always presenting a well-
defined rigid outline, the same unmistakeable definiteness
should be maintained in any attempt to picture such an
object on paper. There should be no “blending'” of
different colour's, no doubtful finish to a tint, no softening
off into the imaginative; every part should present at
once to the eye its form and position, should, in fact,
supply the place of a model of the machine. So impor-
tant a feature is this in mechanical colouring, that when
correct shadows would materially obscure any part of a
machine, they should either be entirely suppressed, or,
where such an omission would be very striking, so
modified as to lessen as much as possible the obscurity
thus produced.

As cast-iron is usually the most extensive component
in every large machine, we will give priority to this
material in our description of the different colours to
be used in representing the various metals of which
machinery is composed.

The colour of a casting fresh from the foundry is com-
monly a very dark bluish-black, having blended with it
an almost imperceptible brownish-green tint or cast. To
represent the casting on paper to the best advantage, the
following colours should be employed :—Indian ink and
indigo, with a very slight admixture of lake. This last
ingredient is necessary; for Indian ink, being actually
only a very dark brown, it would, in conjunction merely
with a blue, impart too green a cast to the tint sought to
be realized. As near an approximation to the natural
tint of cast-iron as can be obtained by the process of
printing in colours, is shown on Plate 66.

Great care should be taken in mixing these colours.
First, the lake—crimson is preferable—should be rubbed
on the pallet; about half-a-dozen turns of the hand are
sufficient, as too much of this colour would impart a rusty
appearance to the desired tint. The indigo may then be
added, and lastly the Indian ink. The quantity of lake
being very inconsiderable, about two-thirds of the mix-
ture should be composed of Indian ink, and the remain-
ing third of indigo. This proportion, however, will be
best ascertained by occasionally trying the tint on a
scrap of drawing paper during the process of mixing.
When the tint appears to have approximated as near as
possible, according to the colourist's judgment, to the tint
described above, its ingredients should be well mixed
together with the brush. The more intimate this inter-
mixture of the colours can be rendered the better; for if
any considerable number of particles of the same colour
remain together, the tint, when essayed, will present a
streaky, semi-party-coloured appearance. It is necessary
to devote at least two minutes to this operation. The

tint being thus prepared, should be left for a short time
untouched, so as to allow the grosser particles of colour
to settle at the bottom of the saucer. No fear need be
entertained of getting the tint too dark, or of mixing too
much ; on the contrary, it is better to compound a con-
siderable quantity and very dark in one saucer, and then
gently pour a little into one or two others, in which, with
varying quantities of water, different gradations of tint
may be produced. The tint left in the first pallet should
be preserved for shading or for shadows, and when it has
become dry, should by no means be discarded, as it will
always be serviceable, and, indeed, preferable for impart-
ing the lesser dark effects to various parts of the drawing.

With one or two exceptions, which will Be pointed out
later, this tint, variously modified, is the only one to be
employed for the representation of cast-iron. It is
adapted as well for expressing the shades and shadows,
as for depicting the body colour. If the shades and
shadows be indicated by Indian ink alone, the small
amount of “brilliancy" which cast-iron naturally enjoys,
will disappear wherever covered with Indian ink, and
even the effect of the body colour will be very sensibly
diminished.

The first parts of the drawing of a machine which it is
usually most judicious to colour, are those of a circular
form — cylinders, the more important shafts, &c. The
rods and smaller shafts, especially where they cross other
parts of the machine, may be left until the other work
is finished.

Taking for granted that the learner has practised the
art of shading according to the simple methods previously
described, and, therefore, that he is somewhat acquainted
with the use of the brush, we will now proceed to colour
a circular casting, it being with cast-iron only that we
have to do at present.

Imagine this casting to be a large cylinder. First
draw two faint pencil lines, to indicate the extremes of
light and shade on its surface* Pass the brush, mode-
rately full of the darkest tint, down the line of deepest
shade, spreading the colour more or less on either side,
according to the diameter of the cjdinder; then, if pos-
sible, before this layer of tint is dry, towards the line of
extreme light, beginning at the top, and encroaching
slightly over the edge of the first tint, lay on another not
quite so dark, but about double its width. It may be
observed, that it is not very essential to put on the second
tint before thq first is dry, for the latter should be so dark
and thick, that its edges may be easily softened at any
time. Whilst this second tint is still wet, with a much
lighter colour in the brush, proceed in the same manner
with a third tint, and so on, until the line of extreme
light is nearly attained. Repeat this process on the
other side of the first tint, approaching the outline of the
cylinder with a very faint wash, so as to represent the
reflected light which progressively modifies the shade as

* Having in preceding sections prescribed rales for establishing
the position of these lines, and for the projection of shadows, their
repetition here would be supererogatory.
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