m ©©mm ©mm
1
YELLOW
MAGENTA
CYAN
MAGENTA
CYAN
YELLOW
MAGENTA
o1-
YELLOW
MAGENTA
CYAN
CYAN
Y1
YELLOW
MAGENTA
CYAN
N
design and reproduction:
ÜG CARTOGRAPHY DEPARTMENT
wmmm
cyan white
yellow
black
white
black
fig.6
yellow
The colour solid
In theory, any colour can be produced by printing various tints of the
printing primaries, yellow, magenta and cyan, on top of each other on
white paper. The printing inks must be transparent, so that they act as
filters. In practice the ränge of colours achieved is limited, because -
a) the inks are not spectrally pure, nor fully saturated, nor perfectly
transparent;
b) varying tints are achieved by using a limited series of percentage
dot screen tints.
Because of these factors:
a) the three füll (solid) inks printed one on top of the other produce
dark brown, not a true black, and equal tints of each ink together
produce lighter brown, not grey.
b) 'cool' colours (bluish colours) are under-represented compared to
'warm' colours (orange - red colours);
c) no very highly saturated colours can be produced;
d) colour combinations are limited by the number of percentage tints
used.
In this Chart, five percentage tints plus füll colour (100%) of each of
yellow, magenta and cyan are used. These give 343 colours, when
combined, including the white of the paper. Each of these colours is
visibly distinct.
The simplest way to arrange these colours is in the form of a cube (see
figure 1Three of the faces each have combinations of two of the inks
i.e. yellow plus cyan produce green, cyan plus magenta produce blue
and magenta plus yellow produce red. The remaining three faces are all
combinations of one solid ink plus varying tints of the other two. Other
combinations are arranged internally within the cube. To render these
visible, the cube has to be 'sliced' into a series of planes, or eise a series
of 'nesting' cubes must be produced. In the latter case, for each cube,
any three faces with a common corner can be transformed into a hexa-
gon for printing on a sheet of paper.
Figure 2 shows such a transformation for three faces of the outer cube
with white as the common corner.
The original cube can be transformed into a double cone, or top-shaped
solid (figure 3), with white and black as the poles. This shape, which
gives an arrangement of colours very similar to the Ostwald colour
solid, has several advantages over the cube (see figure 4).
a) The radial arrangement of hues is more obvious than in the cube.
b) Saturation (purity or intensity) increases radially from the central
axis, and the most saturated colours are all positioned on the outer
circle where the cones meet.
c) The central axis is a grey scale, and any line through the solid paral
lel to this axis is a line of varying lightness, with (more or less)
constant hue and Saturation. Note here that since yellow, for exam-
ple, is perceived as being lighter than magenta or cyan, the colour
variable lightness (or value) also varies around the circumference of
the solid.
Colour discs
Figure 5 shows the top-shaped colour solid 'exploded' into a double set
of nesting cones, each of which can be simply transformed into a disc.
Figure 6 shows the outermost top cone, with white at the centre, trans
formed in this way. The close relationship to the hexagon of Figure 2 is
apparent. This disc is colour disc 1 of the colour chart. Colour disc 2 is
the transformation of the bottom outer cone with black at the centre,
minus the outermost colour circle, not repeated for reasons of space.
The other colour discs are transformations of the interior cones, and
colour square 7 is the centre of the colour solid.
Colour blocks
The top-shaped solid can be dissected in various ways. Figure 7 shows
the solid 'sliced' into vertical planes. Colour block A of the colour chart
corresponds to the cyan-red vertical plane, block B to the magenta-
green plane and block C to the yellow-blue plane.
Percentage tints
Many colour Charts use a scale of percentage tints which is intended to
appear equal interval to the human eye. On this chart, however, there is
more emphasis on the lighter tints than on the darker ones, since lighter
colours are more often used as area colours on maps than darker ones.
In addition, only multiples of 5% are used, since other tints are not rea-
dily commercially available.
The percentage tints used in this chart are:
0%, 10%, 20%, 35%, 50%, 70%, 100%.
To avoid moire patterns, the screen tints of each of the three colours are
aligned at 30° to each other eg. yellow 1 5°, magenta 75°, cyan 45°.
Colour codes
The percentage tints used are given the code numbers O (no colour) to
6 (füll colour). For any colour on the chart, the code number for each
printing ink is always given in the order yellow, magenta, cyan. For
example, chart colour 602 has 100% yellow, no magenta and 20%
cyan. It is a yellowish-green.
Figure 8 shows the percentage tints for yellow for colour disc 1A
basically similar pattern is repeated for the other discs, and, with diffe-
rent orientations, for the other two printing colours.
Caution
The colours of this chart can only be matched with certainty if the ope-
rating conditions are the same as at the ITC, namely:
paper: 100 gm lightly coated woodfree offset
ink: DIN scale 16509, van Son inks: yellow 240, magenta 241, cyan
242, black 243.
press: Color Metal Perle Rotary Offset
printing sequence: black, cyan, yellow, magenta
Any change in these conditions may result in different colours on the
map.
Using the chart
If a radius is drawn in the same direction on each colour disc, all
colours on each radius will have the same hue.
The colour discs are composed of concentric colour circles. The
colours of each colour circle have (more or less) constant Satura
tion, though not constant lightness.
In colour discs 1, 3 and 5, the colours become darker and more-
saturated with increasing distance from the centre.
In colour discs 2, 4 and 6, the colours become lighter and more-
saturated outward from the centre. To see the relation to the
(omitted) outer colour circles, each of these discs can be cut out
and placed on discs 13 and 5 respectively.
The colour blocks each include all the variations in lightness and
Saturation of a pair of complementary hues, with a central 'grey'
scale (not a true grey).
To assist in choosing colours from the chart, the follow-
ing hints are supplied:
1Adjacent colours in the colour solid are not always clearly different
from each other on a map, where they may be widely separated,
and their appearance affected by surrounding colours. Care must
therefore be taken in choosing colours from the chart.
2) For a map with light, bright colours, choose colours from disc 1for
dark, intense colours, use disc 2; for medium, dull colours, use
discs 5 and 6.
3) If on a qualitative type map (e.g. planning, Vegetation) it is desired
that no colour should stand out more than the others, colours
should all be chosen from one colour circle, or two neighbouring cir
cles. Conversely, if it is desired that some colour should stand out
very clearly, a more saturated, darker, or lighter colour may be
selected, from a different circle.
4) On a quantitative type map (e.g. population density), the variable
value is the most important. Value scales can be produced having
the same hue e.g. the red scale 110, 220660, 661 665
(11 steps), but the differences between steps may not be big
enough to be clearly seen on the map. Furthermore, the central
colour of such a scale is more saturated than the others, and may
dominate the map. A shorter value scale of red could be as follows:
220, 440, 551, 662, 664.
5) To produce long value scales, hue change is necessary. One
method of selecting suitable colours from the chart is to choose one
disc, and spiral outwards from a starting point near the centre, or
inwards from the circumference. For example, a 9-step yellow-
orange-brown scale can be selected from colour discs 1 and 2 as
follows: 100, 300, 410,.520, 540, 651, 662, 664, 665. Note
that the outer circle of disc 1 has been avoided, because colours in
this circle are highly saturated.
6) A vertical line through the colour solid parallel to the central axis
has constant hue and more or less constant Saturation. Value
scales can be selected in this way from the colour blocks (for yel
low, magenta, cyan, blue, green, red) e.g. 330, 441, 552, 663.
Colour Squares of corresponding position in each colour disc also
have the same hue and Saturation but different values, e.g. 320
(disc 1), 431 (disc 3), 542 (disc 4), 653 (disc 2).
7)
The colour discs may be cut out and smaller ones placed upon lar-
ger ones, rotated if desired, to assist in colour seiection.
PRINTING COLOUR SEPARATIONS
Each numbered circle corresponds exactly
in position to the colour disc with the same
number. The diagrams within each circle
show the percentage tints of yellow, ma
genta and cyan used to produce the colour
Squares of that colour disc. In the Squares
themselves code numbers refer to these
as follows, always in the sequence yellow,
magenta, cyan.
tint
code nr.
0
0
10
1
20
2
35
3
50
4
70
5
100
6
YELLOW
MAGENTA
CYAN
CYAN
1982
o
o
YELLOW u MAGENTA
35
O
MOMHi
yellow
magenta
remainder
outer cube
three faces
[white I
hexagonal projection
of the three faces of the
outer cube
magenta
yellow
green
cyan
green
white
green
magenta
cyan
