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.