960 Subsurface Geologic Methods 



Printers Inks 



Colored printers inks provide a means of coloring large areas with 

 a uniform tone with no evidences of overlap. Since the inks have a 

 grease base, there is no scale change in the map. The method is easy and 

 fast, and the results are nearly as flawless as printing. 



The viscous printers ink is thinned with about three parts of mineral 

 spirits to one part of ink. Thorough mixing is essential. 



Apply the color with a sable artist's round brush of size 6 to 12, 

 depending on the size of the area to be colored. Cover all the surface, but 

 there is no necessity for spreading the ink evenly. When an area of five 

 or six inches square has been covered, lay a double-thickness of facial 

 cleansing tissue flat on the moist color and pat it down so that the excess 

 ink is absorbed. Make a pad or wad of the tissue and wipe and rub all 

 "free" color from the map. When extending the color, overlap the edge 

 previously colored. There will be no visible overlap when this is wiped 

 with the cleansing tissue. 



Better results can be expected if the border areas are colored first 

 with a medium-sized brush not too heavily charged with ink. A larger 

 brush may be used in the central parts. Apply the darkest colors first, 

 and gradually work up to the lightest. If this procedure is followed, no 

 overlaps will show, even where two different colors are involved. 



There is no satisfactory means of removing the printers ink from 

 the paper. Therefore, considerable care must be taken that the color is 

 applied correctly. Maps colored by this method may be soaked in water 

 for cloth mounting without danger of disturbing the colors. Colored 

 areas will "take" colored pencils within a few minutes, but should be 

 given several hours or days to dry before ink lines are attempted. 



The printers inks can be mixed to obtain an infinite variety of shades. 

 Pastel tints are obtained by mixing the colors with the white "transparent 

 base." Colors must be mixed before they are applied to the map because, 

 as suggested earlier, the paper becomes charged with the first color ap- 

 plied and is, thereafter, resistant to further applications. Within reason- 

 able limits, the viscosity of the color has no effect on the hue or tone on 

 the map: i.e., the same color is obtained with either a thin or thick mixture. 



Pencil Shading of Isopach Maps 



Shadowgraphic maps and the methods of drawing them have been 

 described. Similar use of a soft pencil can add much to the over-all 

 legibility of isopach maps, as shown in figure 519. Thick areas are dark- 

 est, thin ones lightest. About four different tones are most effective. The 

 texture of the map paper determines to a considerable extent the hard- 

 nesses of pencils that should be used. On medium-weight Ozalid black-line 

 paper, hardnesses of 2B to 2H are satisfactory. The toning is accomplished 

 by rubbing the graphite with a charcoal stump blender, as described for 



