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.— Windsor 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.
