Every Plate in each series of broken colors (′ to ′′′′′) contains
exactly the same percentage of neutral gray in each color, the relative
amount increasing progressively in the several series, as shown in the
following table. The percentages of white in the tints and of black in
the shades of the tone scales are in all cases exactly the same as in
the tone scales of pure colors.
SERIES. PERCENTAGES.
Color. Neutral Gray.
Pure Colors 100
(′) 68 32
(′′) 42 58
(′′′) 23 77
(′′′′) 10 90
(′′′′′) 4.5 95.5
Neutral Gray 100
TABLE OF PERCENTAGE OF BLACK AND WHITE IN THE DIFFERENT TONES OF CARBON
GRAY.
TONE NUMBER. PERCENTAGES.
Black. White.
1 100
2 98 2
3 94.5 5.5
4 89.5 10.5
5 83 17
6 75 25
7 67.5 32.5
8 58.5 41.5
9 47 53
10 30 70
_Note._—The percentages given in the preceding tables may not in
all cases be precisely those actually contained in the colors on the
Plates, since absolute precision in reproduction is hardly possible.
All that can be claimed is a reasonably close approximation to the
ideal.
DYES AND PIGMENTS USED IN THE PREPARATION OF THE MAXWELL DISKS,
REPRESENTING THE THIRTY-SIX COLORS OF THE PURE SPECTRUM SCALE, FORMING
THE BASIS OF THE COLOR-SCHEME OF THIS WORK.[29]
=Red.=—Devoe's _geranium lake_ (dry), its orange hue neutralized by a
wash of _rhodamin b._ (_Crocein scarlet b._ washed with _rhodamin b._
produces practically the same fine red.)
=Hues between red and orange.=—_Crocein scarlet b._ with _gold orange_.
=Orange.=—_Gold orange_ with _orange g._
=Hues between orange and yellow.=—_Orange g._ with _auramin_.
=Yellow.=—_Auramin_, rather dilute. (The best substitute among pigments
is a fine quality of _zinc yellow_, as Hatfield's.)
=Hues between yellow and green.=—_Auramin_ washed with _light green_.
=Green.=—_Auramin_ (very dilute) washed with _light green_. (The
auramin should be applied first, because it "sets" or becomes fast
quickly, while the light green does not, but is largely removed by
overwashes of the yellow, thus rendering it very difficult to get the
desired hue.)
=Hues between green and blue.=—_Methyl green_; the same washed with
_light blue_ (Diamond Dye); for the hues nearer blue, _light blue_
washed with Winsor and Newton's _permanent blue_ or _new blue_ (the
least violet-hued of the artificial ultramarines).
=Blue.=—_Light blue_ washed with _permanent blue_ or _new blue_.
(Although the color is nearer that of the artificial ultramarines
named, it is useless to apply the latter first, for overwashes of the
light blue merely sink through and darken the color without improving
the hue. A moderately saturated solution of the light blue should be
applied first, and when this is dry covered with one or more rather
thin washes of the permanent blue or new blue).
=Hues between blue and violet.=—Winsor and Newton's _permanent blue_
and some of the more violet-hued artificial ultramarines, the hues
nearer violet washed with _crystal violet_ or _gentian violet_.
=Violet.=—_Crystal violet._
=Hues between violet and red.=—_Methyl violet 1b._ washed with
_rhodamin b._; for hues nearer red, _rhodamin b._ with Devoe's
_geranium red_ (dry) or _crocein scarlet b._
While more or less similar in hue to rhodamin b., several other aniline
dyes, as _acid fuchsin_, _rubin s._, _rosein_, _magenta_, etc., do not
combine satisfactorily with the violets, the mixture soon becoming dark
or dull and none of them are quite as pure a purple or red-violet.
It is most important to remember that disks thus colored must be
carefully protected from light when not in actual use and _never_
exposed to direct sunlight. The artificial ultramarines are, of course,
permanent, and so, practically, are crocein scarlet, gold orange,
orange g., and auramin—that is to say, are not materially affected
by the action of light except after very prolonged exposure, though
the last named undergoes a change of hue; but the green and violet
aniline dyes are all very evanescent, rapidly fading and eventually
disappearing; light blue and rhodamin, while sensitive to light, are
far less so than the greens and violets.