Subsurface Maps and Illustrations 959 



tone of clear color is achieved as follows: It is necessary to have at hand 

 a few paper charcoal stumps (blenders) of sizes 4 to 8, which can be 

 purchased at any artists' supply store. Dip the stump in white gasoline, 

 Ijenzine, or dry cleaning fluid; and, after the excess on the surface has 

 soaked in, rub the stump over the penciled area with a light, fast circular 

 motion. The solvent dissolves the wax and carries the pigment into the 

 absorbent paper. This process produces a water-resistant color on the 

 map. When the solvent in the map paper has evaporated, a second appli- 

 cation of color and solvent may be applied if darker tones are desired. 

 A dark tone can be graded imperceptibly into a lighter one in this manner; 

 or two colors may be so graded, one into the other. After the wax-pencil 

 coloring has been treated with solvent, it has no tendency to rub off". 



Indelible Pencils 



The indelible colored pencil, sometimes called a "water color pencil," 

 is soluble in water but is relatively unaffected by the aromatic solvents 

 used with the wax-base pencils. The method of application is identical to 

 that described above, except that the blender is used dry. The indelible 

 pencil spreads easily and rapidly with either a dry stump or a wad of 

 facial cleansing tissue or blotting paper. 



For maps that are to serve only a temporary use, the indelible pencil 

 is better than the crayon pencil. The indelible pencil is especially useful 

 in preliminary work which may have to be revised, for the color can be 

 removed with a soft rubber eraser even after blending with a stump. On 

 the other hand, it rubs off" on clothing or other maps, and changes to 

 brilliant hues on contact with even small amounts of water. Perspiration 

 from the hands will cause unsightly blotches on the map; therefore, 

 when there is danger of this blotching, colored portions should be covered 

 while work is in progress. 



Water Color 



Transparent water colors may be applied as a wash on Ozalid prints, 

 but they are diflScult to use and may cause appreciable shrinkage and 

 distortion of the map scale. The air brush is an efficient and generally 

 satisfactory method, although it may cause some shrinkage. When using 

 the air brush one should mask all the map except the portion that is to 

 be colored. Heavy wrapping paper is used for this purpose. For litho- 

 facies maps, slotted stencils can be cut from stiff paper or cardboard. 

 The stencil is laid over the exposed part of the map and the air brush, 

 set on a wide spray, colors the map in bands. When the first color is dry, 

 the stencil is offset one space and the second alternating color is applied. 

 If three color bands are required, two stencils are needed. They are placed 

 one on top of the other and are shifted until the desired exposure of the 

 map surface is attained. 



