THE SAND-BLAST. 



307 



moved, leaving the glass exposed, showing the exact form of the pat- 

 tern. The plate is then removed and placed upon a second table, 

 where it receives over its entire surface a thin layer of melted wax. 

 When this wax has become sufficiently hardened, a knife is introduced 

 beneath the portions of foil that .remain, and these are gently lifted 

 and removed with the wax immediately over them. What remains 

 now is the original pattern traced in wax and resting on the glass. 

 The plate thus prepared is then placed on the moving belts, or feeders, 

 of the large machine and by them is conveyed under the falling sand- 

 blast. Of course, this sheet of sand strikes with eqiial force on the 

 whole surface ; but where the wax layers intervene they act as shields, 

 receiving the sand but checking its progress, while the exposed por- 

 tions being glass, and therefore brittle, are roughened so as to present 

 the appearance of a ground surface. After each plate passes through, 

 it is again slightly heated, the wax removed, and the final appearance 

 is such as indicated in Fig. 5. These illustrations, it may be stated, 

 are from photographic imprints, taken from actual plates, and, as such, 

 indicate with j^erfect exactness the character of the work. In these 

 the light portions represent the ground or depolished surfaces, while 

 the dark lines are those which, having been protected by the stencil 

 shield of wax, were untouched. 



Fig. 6. Machine operated by Exhaust instead of Blast. 



When the surfaces to be acted upon are curved, as in the case of 

 globes, tumblers, etc., a special device is needed. The feature of 

 this is an exhaust-chamber, by the aid of which the sand is drawn up 

 through a tube and projected upward, as shown in Fig. 6. Immedi- 



