. The Bell System technical journal . de of the plate. Division of coatings along thelongitudinal axis is essential on flexure mode crystals in order to make theplate vibrate in flexure. Typical divisions of coating can be noted on thecrystals shown in Figure In the case of the flexural crystal the divid-ing line is carried around the wire attachments in such a manner that eachof the divided surfaces is connected to one of the wires. One method fordividing coating involves the use of a low voltage (two to three volts)impressed between the coating to be divided and a stylus.^ When the fin
. The Bell System technical journal . de of the plate. Division of coatings along thelongitudinal axis is essential on flexure mode crystals in order to make theplate vibrate in flexure. Typical divisions of coating can be noted on thecrystals shown in Figure In the case of the flexural crystal the divid-ing line is carried around the wire attachments in such a manner that eachof the divided surfaces is connected to one of the wires. One method fordividing coating involves the use of a low voltage (two to three volts)impressed between the coating to be divided and a stylus.^ When the finepoint of the stylus is brought in contact with the silver plating and movedalong the desired line of division, the silver is burned away, leaving a smal W. L. Bond, Pat. M 2,248,057. 244 BELL SYSTEM TECHNICAL JOURNAL gap in the plating between 8 and 18 mils wide depending upon the point ofthe stylus. Following the burning operation, the plate is immersed in aphotographic hypo solution to remove all traces of the burned residue after. Fig. —Tool for dividing plating (electric stylus). which it is carefully washed and rinsed in water and dried. In this processit is important that the plates are not kept in the h^-po solution for longerthan two or three minutes, otherwise discoloration of the silver coating will PLATED QUARTZ CRYSTAL UNITS 245 result. The gap in then tested for presence of metallic particles by grad-ually impressing voltages up to 1000 volts a-c across it. If no fiashoveroccurs the division is satisfactory. If flashover occurs the voltage ismaintained until the slivers are burned out. The hypo and burning treat-ments are repeated until a good division is obtained. Figure shows anelectric dividing tool developed for this purpose. In using this method ithas been found that the arc at the point of the stylus may cause twinningof the quartz to a minor extent along the dividing hne. This effect isusually insignificant although it may be objectionable especi
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