rust, brown, and gray-brown are not hues. The hue of a color is not altered by 

 the addition of white, gray, or black — the neutrals. 



Value (tone) 



The value or tone of a color is the degree of lightness or darkness. A red 

 hue is not altered by adding white, but the value is changed. Values may be 

 expressed in terms of neutral tones from black to white. Thus, a color, such 

 as red, may have the same value as a dark gray, depending upon its degree of 

 darkness. Colors of low value are called shades; those of high value, tints. 



Intensity (chroma) 



The intensity of a color is its purity. The intensity of color is reduced by 

 the addition of neutralizing elements, such as gray or white. The intensity of 

 rock color is generally low because of the presence of neutralizing agents, and 

 the matching of rock color must take this fact into account. 



If colored pencils in red, blue, and yellow closely approach the primary 

 colors, almost any color can be obtained with them simply by mixing in 

 various proportions; but in order to produce all tints and shades, the neutral 

 factors must be added. The neutral "colors" in log work are made by lead 

 pencils in several degrees of hardness or tones. 



It was stated above that all colors possess three qualities; hue, value, and 

 intensity. If the part each plays in producing the colors observed in rocks is 

 understood, the rock colors will be more easily analyzed; hence, they will be 

 more easily described and duplicated in whatever medium is used. A few 

 illustrations of the fundamental properties will show their interrelationships and 

 their individual effects on the colors observed. 



A mixture of yellow and blue results in green. The proportions of the 

 blue and yellow determine the hue. A small amount of yellow and a large 

 amount of blue will produce a green-blue; if the proportions are reversed, the 

 hue will be a green-yellow. The same principle holds for the orange group 

 obtained with red and yellow, or the purple group obtained wth red and blue, 

 as, for example, purple, red-purple, purple-blue, and the like. All these inter- 

 mediates, as well as the primaries, are hues. 



Starting with the hue orange-red in comparatively pure pigment, the value, 

 or brightness, can be increased by the addition of white. The hue is not changed. 

 When colored pencils are used, the value is raised simply by applying less 

 color to the white paper. The value is lowered by adding gray pencil to the 

 hue established with the colored-pencil mixture. 



The intensity of color is its degree of purity or lack of neutralizing factors. 

 The intensity of a color should not be confused with its value or brightness. 

 For example, the pure orange-red hue has the highest intensity, but only medium 



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