_SHADING AND COLORING DRAWINGS._
The shading or coloring of drawings by tints is more employed in large
drawings than in small ones, and in Europe than in the United States;
while on the other hand tinting by means of line-shading is more
employed in the United States than in Europe, and more on small drawings
than on large ones.
Many draftsmen adopt the plan of coloring the journals of shafts, etc.,
with a light tint, giving them the deepest tint at the circumference to
give them a cylindrical appearance. This makes the drawing much clearer
and takes but little time to do, and is especially advantageous where
the parts are small or on a small scale, so that the lines are
comparatively close together.
For simple shading purposes black tints of various degrees of darkness
may be employed, but it is usual to tint brass work with yellow. Cast
iron with India ink, wrought iron with Prussian blue, steel with as
light purple tint produced by mixing India ink, Prussian blue and a
tinge of crimson lake. Copper is tinted red. On plane surfaces an even
tint of color is laid, but if the surfaces are cylindrical they are
usually colored deeper at and near the circumference, and are tinted
over the colors with light tints of India ink to show their cylindrical
form.
If a drawing is to be colored or shaded with India ink the paper should
be glued all around its edges to the drawing board, and then dampened
evenly all over with a sponge, which will cause the paper to shrink and
lay close to the surface of the drawing board. If, in applying a color
or a tint, the color dries before the whole surface is colored, the
color will not be of an equal shade; hence it is necessary before
applying the color to dampen the surface, if it is a large one, so that
the color at one part shall not get dry before there has been time to go
over the whole surface; a more even depth of color is attained by the
application of several coats of a light tint, than with one coat, giving
the full depth of color. But if the paper is not allowed to dry
sufficiently between the coats, or if it has been made too wet previous
to the application of the colors, it will run in places, leaving other
hollows into which the color will flow, making darker-colored spots. To
avoid this the paper may be dried somewhat by the application of clean
blotting paper.
To maintain an even shade of color, it is necessary to slightly stir up
the color each time the brush is dipped into the color saucer or
palette, especially when the coloring is composed of mixed colors,
because the coloring matter is apt to separate from the water and sink
to the bottom.
So, also, in mixing colors it is best to apply the end of the color to
the surface of the palette and not to apply the brush direct to the cake
of color, because the color is more completely mixed by contact with
the palette than it can be by the brush, which may retain a speck of
color that will, unless washed out, make a streak upon the drawing.
To graduate the depth of tint for a cylindrical surface, it is best to
mix several, as, say three depths or degrees of tint, and to first use
the darkest, applying it in the direction in which the piece is to be
shaded darkest. The width this dark application should be is obviously
determined by the diameter of the piece. The next operation is to
lighten or draw the part, line or streak thus dark colored, causing it
to get paler and paler as it approaches the axial line of the piece or
cylinder. This lightening is accomplished as follows: The dark streak is
applied along such a length of the piece that it will not dry before
there has been time to draw it out or lighten it on the side towards the
axis. A separate brush may then be wetted and drawn along the edge of
the dark streak in short strokes, causing the color to run outwards and
become lighter as it approaches the axis. It will be found that during
this process the brush will occasionally require washing in water,
because from continuous contact with the dark streak the tint it
contains will darken. When the first coat has been laid and spread or
drawn out from end to end of the piece, the process may be repeated two
or three times, the most even results being obtained by making the first
dark streak not too dark, and going over the drawing several times, but
allowing the paper to get very nearly dry between each coat. In small
cylindrical bodies, as, say 1/4 inch in diameter, the darkest line of
shadow may be located at the lines representing the diameter of the
piece, but in pieces of larger diameter the darkest line may be located
at a short distance from the line that denotes the diameter or perimeter
on the shadow or right-hand side of the piece, as is shown in many of
the engravings that follow. It is obvious that if a drawing is to have
dimensions marked on it, the coloring or tinting should not be deep
enough to make it difficult to see the dimension figures.
The size of the brush to be used depends, of course, upon the size of
the piece to be shaded or colored, and it is best to keep one brush for
the dark tint and to never let the brush dry with the tint in it, as
this makes it harsh. In a good brush the hairs are fine, lie close
together when moistened, are smooth and yet sufficiently stiff or
elastic to bend back slightly when the pressure is removed. If, when
under pressure and nearly dry, the hairs will separate or the brush has
no elasticity in it, good results cannot be obtained. All brushes should
be well dried after use.
The light in shading is supposed to come in at the left-hand corner of
the drawing, as was explained with reference to the shade line.
Excellent examples to copy and shade with the brush are given as
follows:
Figure 300 represents a Medart pulley, constructed by the Hartford Steam
Engineering Company; the arms and hub are cast in one piece, and the rim
is a wrought iron band riveted to the arms, whose ends are turned or
ground true with the hub bore. The figure is obviously a wood engraving,
but it presents the varying degrees of shade or shadow with sufficient
accuracy to form a good example to copy and brush shade with India ink.
Figure 301 represents a similar pulley with a double set of arms,
forming an excellent example in perspective drawing, as well as for
brush-shading.
[Illustration: Fig. 300.]
In brush-shading as with line-shading, the difficulties increase with an
increase in the size of the piece, and the learner will find that after
he has succeeded tolerably well in shading these small pulleys, it will
be quite difficult, but excellent practice to shade the large pulley in
Figure 302.
One of the principal considerations is to not let the color dry at the
edges in one part while continuing the shading in another part of the
same surface, hence it is best to begin at the edge or outline of the
drawing and carry the work forward as quickly as possible, occasionally
slightly wetting with water edges that require to be left while the
shading is proceeding in another direction.
[Illustration: Fig. 301.]
When it is required to show by the shading that the surfaces are highly
polished, the lighter parts of the shading are made to contain what may
be termed splashes of lighter and darker shadow, as in Figure 303, which
represents an oil cup, having a brass casing enclosing a glass cylinder,
which appears through the openings in the brass shell.
Figure 304 represents an iron planing machine whose line-shading is so
evenly effected that it affords an excellent example of shading. Its
parts are similar to those shown in the iron planer in Figure 297, save
that it carries two sliding heads, so as to enable the use,
simultaneously, of two cutting tools.
[Illustration: Fig. 304. (Page 282.)]
[Illustration: Fig. 302.]
A superior example in shading is shown in Figures 305 and 306, which
represent a plan and a sectional view of the steam-cylinder of a Blake's
patent direct-acting steam-pump. The construction of the parts is as
follows: A is the steam-piston, H 1 and H are the cylinder
steam-passages; M is the cylinder exhaust port.
[Illustration: Fig. 303.]
[Illustration: Fig. 305.]
The main valve, whose movement alternately opens the ports for the
admission of steam to, and the escape of steam from, the main cylinder,
is divided into two parts, one of which, C, slides upon a seat on the
main cylinder, and at the same time affords a seat for the other part,
D, which slides upon the upper face of C. As shown in the engravings, D
is at the left-hand end of its stroke, and C at the opposite or
right-hand end of its stroke. Steam from the steam-chest, J, is
therefore entering the right-hand end of the main cylinder through the
ports E and H, and the exhaust is escaping through the ports H 1, E 1, K
and M, which causes the main piston A to move from right to left. When
this _piston_ has nearly reached the left-hand end of its cylinder, the
tappet arm, T, attached to the piston-rod, comes in contact with, and
moves the valve rod collar O 1 and valve rod P, and thus causes C,
together with the supplemental valves R and S S 1, which form, with C,
_one casting_, to be moved from right to left. This movement causes
steam to be admitted to the left-hand end of the supplemental cylinder,
whereby its piston B will be forced towards the right, carrying D to the
opposite or right-hand end of its stroke; for the movement of S closes N
(the steam-port leading to the right-hand end), and the movement of S 1
opens N 1 (the steam-port leading to the opposite or left-hand end), at
the same time the movement of V opens the right-hand end of this
cylinder to the exhaust, through the exhaust ports X and Z. The parts C
and D now have positions opposite to those shown in the engravings, and
steam is therefore entering the main cylinder through the ports E 1 and
H 1, and escaping through the ports H, E, K and M, which causes the main
piston A to move in the opposite direction, or from left to right, and
operations similar to those already described will follow, when the
piston approaches the right-hand end of its cylinder. By this simple
arrangement the pump is rendered positive in its action; that is, it
will instantly start and continue working the moment steam is admitted
to the steam-chest, while at the same time the piston is enabled to move
as slowly as the nature of the duty may require. It will be noted that
in Figure 305, the ports of C are shown through D, whose location is
marked by dark shading. This obviously is not correct, because D being
above C should be shaded lighter than C, and again the ports E 1 and K
could not show dark through the port D. They might, of course, be shown
by dotted outlines, but they would not appear to such advantage, and on
this account it is permissible where artistic effect is sought, the
object being to subserve the shading to making the mechanism and its
operation clearly and readily understood.
[Illustration: Fig. 306.]
Figure 307 affords another excellent example for shading. It consists of
an independent condenser, whose steam-cylinder and valve mechanism is
the same as that described with reference to Figures 305 and 306.
[Illustration: Fig. 307. (Page 288.)]
[Illustration: Fig. 308. (Page 289.)]
[Illustration: Fig. 309. (Page 289.)]
[Illustration: Fig. 310--SECTION OF CYLINDER AND STEAM CHEST. (Page
289.)]