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BELL SYSTEM TECIIXICAL JOURNAL 



The figures produced on Z-cut surfaces are small and complex, (hardly 

 usable) unless a considerable amount of free HF acid is added. Etch-figures 

 here considered are those produced on the pin-hole instrument, and are us- 

 able only if they have such character as will permit of their use in determin- 

 ing quartz axes. Fig. 5.21 shows the type of usable etch-figure obtained on 

 X-cut sections with an ammonium bifluoride and sugar solution (the sugar 

 is here effective mainly in preventing creepage of the solution). It might 



HQ+XUP 



RHQ -X U 



LHQ.+X U 



HQ,-XUP 



B 



Fig. 5.21— Etch-figures obtained on the pin-hole oriascope with X-cut sections which 

 have been strongly etched in bifluoride mixtures, or e.xcessively etched in hydrofluoric acid. 

 These etch-figures differ from those of Fig. 5.19 (for a moderate etch in hydrofluoric acid) 

 but are obviously usable. 



be noted that a similar figure is obtained with hydrogen fluoride gas, and 

 with excessively long etching (several hours) in hydrofluoric acid. 



When the bifluorides are used only to develop reflection contrast in the 

 detection of twmning, their effectiveness appears to be about the same as 

 hydrofluoric acid, under equivalent process conditions. The etching power 

 of the bifluorides may be maintained nearly constant over a long period of 

 use by maintaining an excess of the salt in solution, a distinct advantage 

 over the acid. The metals copper, nickel, brass and stainless steel may be 

 used in fabricating tanks and racks, lead and steel are inferior. 



Finished quartz surfaces are sometimes etched to remove surface debris 



