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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ENGINEER AND MACHINIST’S DRAWING-BOOK.

the gearing partly enters. The gearing itself, and more
especially the shadows on it, those, for instance, which
fall on the feathers of the wheels, should be darker than
usual, so as to bring them forward and add to the appa-
rent depth of the recess beneath them.

The amount of light and reflection on the members of
a machine should diminish in intensity as the distance of
such objects from the spectator increases. This may be
observed to some extent on Plates Ixiv. and lxv., Elevation
of a double blowing engine. Indeed, on the distant mem-
bers of such a large engine all bright lights ought entirely
to disappear. As it is necessary for effect, to render, on
those parts of a machine nearest the eye, the contrast of
light and shade as intense as possible, so, for the same
object, the light and shade on the remotest parts should
be subdued and blended according to the extent or size
of the machine.

A means of adding considerably to the definiteness of a
coloured mechanical drawing, and of promoting, in a re-
markable degree, its effective appearance, is obtained by
leaving a very narrow margin of light on the edges of all
surfaces, no matter what may be the angles which they
may form with the surfaces that join them. This should
be done invariably; we do not even except those edges
which happen to have shadows falling on them; in such
cases, however, this margin, instead of being left quite
white, which would have a harsh appearance, may be
slightly subdued. The locomotive wheel, Plate lx., affords
a very apt exemplification of the pleasing aspect which
this gives to the drawing. In the case referred to such
an absence of tint is really necessary to show clearly the
different surfaces of the wheel, which, deprived of these
lights, would look flat and doubtful. The difficulty of
achieving this effect, of imparting a clear, regular, un-
broken appearance to these lines of light, seems very for-
midable, and, indeed, nearly insuperable. The hand of
the colourist may be as steady and confident as a hand
can be, and yet fail to guide the brush, at an almost in-
appreciable distance from a straight or circular line, with
that precision and sharpness so requisite for the accurate
delimitation of this beautiful effect. We shall, however,
explain a novel and effective method of arriving at this
most desirable result.

Suppose the object about to receive the colour to be the
elevation of a long flat rod or lever, on the edge of which
a line of light is to be left. Fill the drawing pen as full
as it will conveniently hold with tint destined to cover
the rod or lever, and draw a broad line just within, but
not touching, the edge of the lever exposed to the light.
As it is essential for the successful accomplishment of the
desired effect that this line of colour should not dry, even
partially, until the tint on the whole side of the lever has
been put on, it will be as well to draw the pen again veiy
lightly over the same part, so that the line may retain as
much tint as possible. Immediately this has been done,
the brush, properly filled with the same tint, is to pass
along and join the inner edge of this narrow strip of
colour, and the whole surface of the lever filled in. Thus

a distinct and regular line of light is obtained, and, in fact,
the lever, or whatever else the object may be, covered in
a shorter time than usuaL A still more expeditious way
of colouring such surfaces is to draw a second line of colour
along and joining the opposite edge of the lever or other
object, and then expeditiously to fill in the intermediate
space between the two wet lines, by means of the brush.
In this manner a clear uniform outline to the tint is ob-
tained, which could not be effected in any other way. As
celerity in the movements of the colourist is very neces-
sary to carry out properly this method of leaving a light-
edge to the boundaries of flat surfaces, and as confidence
in possessing the requisite ability to perform it must pre-
cede success—a little practice is desirable before essaying
it on any drawing of importance. The blades of the draw-
ing pen must not be sharp, and the pen should be used
with great precaution and delicate lightness, otherwise
the blades will cut more or less the paper and leave their
course visible—an unsightly betrayal of the mechanical
means employed to obtain such regularity in the colour-
ing. Flat circular surfaces may be treated in the same
manner, by using the pen-compass in place of the draw-
ing pen. When such surfaces are rather extensive, it will
be judicious to colour them in halves, or in quadrantal
spaces, taking great care, when joining the parts together,
that they may overlap or fall short of each other as little
as possible. The appearance of these junctions may be
obliterated by slightly washing them, or by going over
the whole surface with a very light tint, and, in passing,
gently rubbing the seams with the brush By similar
means the line of light on a cylinder, shaft, or other cir-
cular body may be beautifully expressed. To indicate
this light with perfect regularity is highly important, for
if a strict uniformity be not maintained throughout its
whole length, the object will look crooked or distorted.
After having marked in pencil, or guessed the position of
the extreme light, take the drawing pen, well filled with
a just perceptible tint, and draw a line of colour on one
side the line of light, and almost touching it; then with
the brush, filled with similar light tint, join this line of
colour whilst still wet, and fill up the space unoccupied by
the shade tint, within which the very light colour in the
brush will disappear. Let that part of the object on the
other side of the line of light be treated in the same way,
and the desired effect of a stream of light clear and mathe-
matically regular will be obtained. The effectiveness and
expedition of this method will be most obvious in colour-
ino- Ion o' circular rods of small diameter, where the want
of accuracy is more immediately perceptible. The ex-
treme depth of shade, as well as the line of light on such
rods may, with great effect, be indicated by filling the
pen with dark shade tint, and drawing it exactly over the
line representing the deepest part of the shade. On either
side and joining this strip of dark colour, another, com-
posed of lighter tint, is to be drawn. Others successively
lighter are to follow, until, on one side, the line of the rod
is joined, and on the other the lightest part of the rod is
nearly reached. The line of light is then to be shown, and
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