Dyes and. Pigments for Maxwell Disks. 21 



for over washes 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 arti- 

 ficial ultramarines, the hues nearer violet washed with 

 crystal violet or gentian violet. 



Violet.— Crystal violet. 



Hues between violet and red.— Methyl violet lb. 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 expo- 

 sure, though the last named undergoes a change of hue; 

 but the green and violet aniline dyes are all very evanes- 

 cent, rapidly fading and eventually disappearing; light 

 blue and rhodamin, while sensitive to light, are far less 

 so than the greens and violets. 



