962 Subsurface Geologic Metviods 



production^ An exceptionally well drawn map may lose much of its effect- 

 iveness in reproduction if certain principles in drafting are neglected. 



The so-called photo-copy processes depend upon the transmission of 

 light through the medium upon which the map is drawn. The lines and 

 figures drawn on the map prevent the light from passing through and 

 exposing those portions of the sensitized printing paper. It is, therefore, 

 desirable for the lines to be opaque and the medium transparent or highly 

 translucent, and the quality of prints will depend largely on the degree to 

 which these conditions are met. Obviously the best reproductions will be 

 obtained from drawings made in black drawing ink on transparent ma- 

 terial, such as cellulose acetate. Lines drawn with colored, waterproof 

 inks may look well on the original map, but are liable to be indistinct 

 or discontinuous on the print because these inks are not opaque to the 

 intense lights of the printing machines. If colors must be used on originals 

 to be reproduced by photo processes, the water-soluble types are more 

 satisfactory. When extremely thin lines are necessary on acetate or similar, 

 thick materials, it is better if they are inked on the back side where they 

 will be in direct contact with the printing paper. Thin lines on the upper 

 surface are likely to "burn out" in printing because of diffraction along 

 the edges of the lines. 



Since the necessary exposure time is longer with more opaque media, 

 such as thick vellum, or tracing paper, the opportunity for light leakage 

 along thin lines is greater. 



Photocopies can be made from penciled originals; but it is essential 

 to maintain considerable contrast between the opacity of the tracing ma- 

 terial and the lines. For this reason thin tracing paper with a "toothy" 

 texture combined with pencils which make very black lines give the best 

 results. It is somewhat difficult to make reproducible maps with penciled 

 lines on acetate and tracing linen. 



Good photostats can be made from copy that is too weak to reproduce 

 by light transmission processes. Better reproductions are obtained from 

 originals having high line and background contrasts. Generally speaking, 

 prints by Ozalid and Van Dyke methods are better than photostats for 

 hand coloring by methods described earlier. Photostat prints are more 

 receptive to colored pencils if they are rubbed with drafting pounce or 

 some other very fine abrasive. Of the processes discussed above, only the 

 photostat permits a reduction or enlargement of the original scale. 



Maps and drawings for publication should be drawn to a slightly 

 larger scale than that desired in the reproduction. This is done so that 

 the inevitable irregularities occurring in lines, figures, or lettering will 

 be reduced or eliminated in the reduction of scale. Over-all proportions, 

 however, are not improved in the reproduction; in some cases, faulty pro- 

 portions of map features are even more evident in the reduced reproduc- 

 tion. 



Plain black and white drawings, that is, black lines on a white or blue 



