COMMON HAND-TOOLS 277 



to 120, and the degree of smoothness of surface they leave 

 may be compared to that left by files as follows : 



8 and 10 represent the cut of a wood rasp 



16 " 20 " " " " a coarse rough file 



24 " 40 " " " " an ordinary rough file 



36 " 40 " " " " a bastard file 



46 " 60 " " " " a second-cut file 



70 " 80 " " " " a smooth file 



90 " 100 " " " " a superfine file 



120 F and FF " " " " a dead-smooth file 



316. Polishing and Burnishing. Metal is polished to give 

 it a fine finish and to produce a smooth surface which will 

 reflect light to its highest degree in other words to give it 

 a "shine." The principal substances or abrasives used to 

 produce such a surface are emery, carborundum, rouge, 

 putty powder, silica, and burnishing materials. While 

 emery is not so hard as some other abrasives, it is the strong- 

 est abrading powder. The powder principally used for giving 

 a fine polish to small articles is called rouge, and is composed 

 of ferric oxide. Most polishing compounds contain rouge. 

 Its color and properties depend to a large degree on the tem- 

 perature at which it is manufactured. Rouge made at a 

 low temperature is soft proportionally. For this reason, 

 jewelers' rouge is made at a low temperature, while rouge 

 for polishing iron is made at a high temperature. Putty 

 powder is an oxide of tin. Silica is the oxide of silicon, and 

 is found in different forms: in the crystalline form it is 

 called quartz; in the form of sandstone, which consists of 

 particles of crystalline or rounded silica cemented with 

 silica powdered sand, it is used for grindstones. Artificial 

 polishing stones are made by cementing very fine white sand 

 with shellac or other materials. 



