GLASS-MAKING. 



167 



sage of the light through the transparent portions. But by ob- 

 scuring the entire surface of * the globe, and then cutting even a 

 very modest design upon the background so prepared, the result 

 is much more effective. The transmitted light, from its subdued 

 character, is also more agreeable. The cutting is done in the so- 

 called " mud-box " — a designation which has arisen from the fact 

 that the spent sand or mud from the cutting of heavier articles is 

 here utilized. 



. Fig. 6.— Printing the Designs and Wrapping the Globes, prior to the Etching. 



These processes are all purely mechanical. They depend upon 

 the direct friction between the glass and the abrading powder, or 

 between the glass and the cutting stone, as in the case of the 

 smoothing process. It is possible, however, to bring about this 

 grinding action by less direct pressure. One of these indirect 

 methods — the sand-blast — deserves particular mention, both be- 

 cause of its commercial importance and because of its ingenuity. 

 Some years ago there was published a book which pointed out, 

 with more or less cunning, a prototype in nature for nearly all 

 our mechanical devices. The author did not, I believe, mention 

 the sand-blast, but he might well have done so, for it is a direct 

 imitation, though perhaps an unconscious one, of a process which 

 Nature has been using very effectively ever since the first blast 

 of wind carried the earliest sand-grains against the Eozoic rocks. 

 This natural sand-blast has done not a little in altering the ap- 

 pearance of the face of the earth. In the Rocky Mountains there 

 are many curiously sculptured rocks in the comparatively rain- 

 less districts, which owe their carving almost entirely to this 



