ETCH TECHNIQUE 



29 



tinct portion of the etch-ligures in Test 2. That the observations are so 

 similar for this 20° range of cuts indicates that the nature of the etch-pits 

 on these cuts is very similar, (see Fig. 5.6 for the nature of the etch-pits on 

 AT slabs). The angular arrangement of the Test / optical system makes 

 use of strongly developed facets which are approximately parallel to the X- 

 axis and inclined at an angle of —57.6° to the Z-axis of the quartz. Within 

 experimental error these facets are parallel to the 01.2 atomic planes and 

 hence are called the 01.2 facets. It is also these facets that give the enlarged 



POSITIVE-CUT FIGURES 



TEST 1 (twinning) 



TEST 2 (sense OF CUT) 



NEGATIVE-CUT FIGURES 



Fig. 5.14 — The appearance in the twinoriascope of twinning in Test 1 (two examples) 

 and of the four possible etch-figures in Test 2. The observance (in Test 2) of either of the 

 positive-cut figures indicates that the illuminated portion of the slab is a positive cut, 

 while either negative-cut figure indicates a negative cut. These etch-figures for a CT 

 slab, are not markedly different than those for AT, BT, and DT slabs. 



head of the golf-club, negative-cut figures. The right and left handedness 

 of quartz results in two figures each for the positive and the negative orien- 

 tation. Though it is commonly of no interest, it is possible to determine 

 from the etch-figure observed, both the handedness and the electrical sense 

 of the illuminated portion of the slab. The handedness is as indicated by L 

 and R in each etch-figure of Fig. 5.14, and the electric axis is ± to the right 

 or left as indicated by the -|- and — signs. 



Best etch-figures are obtained m the twinoriascope with fine ground (400 

 carborundun) slabs which have been given a strong etch (40 minutes in 50% 



