36 



BELL SYSTEM TECHNICAL JOURXAL 



size of the etch-figure depends on the whole distance from the pin-hole to the 

 etched top-surface, and hence, may be made as large as desired, by raising 

 the section and fluid level. Xtry thin sections, slabs or plates may be ex- 

 amined similarly, with the bottom surface contacting the immersion fluid, 

 or the plates may be wet with immersion fluid and placed on thick glass 

 plates and placed over the pin-hole. In either case the top etched-surface 

 must be kept dr\'. By this means the twinoriascope examinations described 

 in Section 5.52 might be performed on the pin-hole oriascope, (a disadvan- 

 tage being the necessity of using an immersion fluid). 



Usually etch-figures are obtained from flat etched surfaces whose orienta- 

 tion is known within 5°. However, if the surface be 10° to 20° off'-orienta- 

 tion the etch-figure will be plainly distorted. If now the section be viewed 

 at an angle to the normal position, or if the section be tilted in the fluid- 



A B 



Fig. 5.20 — CLEAVAGE-FIGURES may also be observed on the pin-hole oriascope in 

 ground but unetched specimens, in this case a Z-cut section. Here the direction of the X 

 axes but not their sense (nor handedness, nor twinning) may be determined. 



bath method described above, the undistorted figure may be observed. The 

 direction and amount of misorientation of the surface may be thus esti- 

 mated. By provision of suitable mounts and scales the misorientation could 

 be measured to 5°. 



It might be added that m some cases unetched, ground (or sawn) quartz 

 surfaces give "cleavage-figures." Thus with Z-cut sections which have 

 been ground, but not etched, there may be observed on the pin-hole oria- 

 scope cleavage-figures like those shown in Fig. 5.20. The difference be- 

 tween the two views is mainly a difference in focusing and in photographic 

 reproduction. The cleavage-figure indicates that there are preferential 

 cleavage planes in quartz, which are parallel to the X-axes, and correspond 

 approximately to the natural cap faces. Further, there is no indicated dif- 

 ference between the major and minor planes. Thus, the cleavage-figure is 



