6 Color Standards and Nomenclature. 



gray, these being in reality colored grays; to which are 

 added a scale of neutral gray and one of carbon gray, the 

 former being the gray resulting from mixture of the three 

 primary colors (red 32, green 42, violet 26 per cent., 

 which in relative darkness equals black 79.5, white 20.5 

 percent.); the latter being the gray produced by mix- 

 ture of lamp black and Chinese white, and the scale a 

 reproduction of that in the author's first "Nomenclature 

 of Colors " (1886, Plate II, nos. 2-10), It should be 

 emphasized that in all cases except the scale of carbon 

 grays, only the disks representing the middle horizontal 

 series of colors (both pure and broken) have been used, in 

 combination with a black and a white disk, respectively, 

 to make the colors of the vertical scales of tints and 

 shades. 



The coloring of a satisfactory set of disks to repre- 

 sent the thirty-six pure spectrum colors and hues was a 

 matter of extreme difficulty, many hundreds having been 

 painted and discarded before the desired result was 

 achieved. Several serious problems were involved, the 

 matter of change of hue through chemical reaction of the 

 combined pigments or dyes* (especially the latter) being 

 almost as troublesome as that of securing the proper 

 degree of difference between each adjoining pair of hues. 

 The method by which satisfactory results were finally 

 secured was as follows : First, six disks were colored 

 to represent each of the fundamental spectrum colors, 



*For satisfactory color-wheel work it is necessary to discard practically all the 

 so-called artists' colors, as being much too dull to even approximately represent the 

 colors of the spectrum, and to substitute carefully selected aniline or coal-tar dyes, 

 of which, fortunately, there is a very large number of remarkable purity of hue. 

 Indeed, the work of most color-physicists is vitiated by their use of such crude colors 

 as vermilion, carmine, scarlet-lake, chrome yellow, emerald green, Prussian blue, etc. 

 (For a list of dyes and pigments used in preparing the Maxwell disks representing 

 the thirty-six colors of the chromatic scale, see pages 26, 27.) 



