SCIENCE IN THE INDUSTRIAL WORLD 



for example, the artist wishes to produce a light-gray 

 effect, he may do so by rubbing the crayon lightly over 

 the surface of the stone, and he may intensify this shade 

 to any desired degree by increasing the amount of pres- 

 sure, thus depositing more of the acid-resisting sub- 

 stance ; or he may produce a flat black effect by covering 

 the surface of the stone with ink. 



It will be seen that in this process the lights and 

 shadows are not reversed, the lithographer drawing 

 and shading them in the same manner as would be done 

 in an ordinary drawing, although the composition of the 

 picture is reversed. One of the features of lithography 

 is the remarkable results that may be obtained by its 

 use in color-printing. In principle this printing with 

 many colors is simple enough, but when it is con- 

 sidered that for every color used a separate stone and a 

 separate printing on the same piece of paper is neces- 

 sary, registered so accurately that there will not be the 

 slightest variation in its position as it is placed on the 

 successive stones, the results shown in the finished 

 color-print seem little short of marvelous. 



When a colored picture has to be duplicated by 

 lithography, the lithographer first determines how 

 many colors will be required to produce the desired 

 effect. An outline of the picture is then made of exactly 

 the right size on a stone, and the patches of color are 

 carefully outlined. This stone, which is known as the 

 keystone, determines the exact position of each of the 

 colors as they will appear on the separate stones. Sup- 

 pose the picture to be reproduced is a simple one, 

 using, let us say, five colors. This will necessitate the 



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