ETCH TECHXIQUE 33 



dum), and in both cases a moderate etch, (20 to 30 minutes in 50% HF). 

 It is noted that the spiralhng, outer tails of the etch-hgures (as well as other 

 features) denote the handedness of the quartz. Such handedness features 

 are not as marked with line ground surfaces, nor with weaker etches. The 

 central triangular portion of these ligures is used for alignment of the section 

 with the rulings on the marking arm windows. Since this triangular iigure 

 is misaligned with the X-axes of the quartz by approximately 12°, and in an 

 opposite sense for the two kinds of handedness, there are provided two match- 

 ing arms. One is to be used for left quartz and the other for right quartz. 

 The diagram of Fig. 5.1 7C shows the orientation arrangement of a combina- 

 tion of matching windows and marking template, that results in the section 

 being marked with three radial lines which correspond to the positive X-axes 

 of the quartz. Though this is the most obvious manner of marking Z-cut 

 sections, it is of advantage in practice to obtain a reversed marking on left- 

 hand quartz (by using an oppositely ruled left-hand matching window). 

 By so marking the quartz no further attention need be paid to handedness, 

 see Section 2.4, Chap. 11.'^ In either case the relation of the various plate 

 cuts to the axis markings obtained above, may be determined from Fig. 5.4. 

 Since the etch-tigures give only approximate orientation X-rays are used for 

 the linal determination. That X-rays are not used for the whole determina- 

 tion is as explained in Section 5.1. 



With X-cut sections, having a coarse grind (100 carborundum) and a 

 strong etch (30-45 minutes in 50% HF), the etch-iigures obtained are like 

 those of Fig. 5.19. Here the positive face of the section gives an entirely 

 different ligure than the negative face, as would be expected from the 

 nature of the etch-pits shown in Fig. 5.5. Opposite-handedness gives re- 

 versed ligures. The four possible ligures are oriented with respect to the 

 Z-axis and the major cap face direction of the section "r" as shown in Fig. 

 5.19A and B. The non-parallelism of the Z-axis and the parallel sides of the 

 etch-figures amounts to three to five degrees. This disposition of figures 

 (relative to quartz axes) is taken into account in the design of the matching 

 and marking arms shown in Fig. 5.18, and diagrammed in Fig. 5.19C. The 

 etched X-cut section is rotated on the mounting table, with the central 

 matching arm in position, until the long straight sides of the "parallelogram" 

 figure, or the long parallel lines of the "H" figure, are parallel to the two 

 parallel-lines ruled on the window of the matching-arm (the parallelogram 

 figure is shown so aligned in C). The figure thus used is compared with 

 the four figures sketched on this matching-arm, to determine which of the 

 two marking arms is to be used for marking (note arrows giving this indi- 

 cation). The proper marking arm is lowered onto the section and used to 



^^ The instrument of Fig. 5.16 has a still different arrangement of matching and marking 

 arms. 



