. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. Fig. 12. of the plate, as shown in the illustration (fig. 12).This is known as the Scovill-Levy holder. In some forms of this type of holder, the bars havehad attached to them a rack, so that a central pinionat the side would feed them up and down holder (fig. 13) is on this principle. Inanother pattern there is a rod at each side with aright and left-handed screw cut on it, so that whenengaged with a nut on the bars they move to and fro THE STUDIO. 45 equally. These complic
. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. Fig. 12. of the plate, as shown in the illustration (fig. 12).This is known as the Scovill-Levy holder. In some forms of this type of holder, the bars havehad attached to them a rack, so that a central pinionat the side would feed them up and down holder (fig. 13) is on this principle. Inanother pattern there is a rod at each side with aright and left-handed screw cut on it, so that whenengaged with a nut on the bars they move to and fro THE STUDIO. 45 equally. These complications are, however, quite un-necessary, and are even objectionable where the wetplate process is worked, as the mechanism gets rustedor corroded. For half-tone purposes two pairs of bars are pro-vided, working independently of each other, one pair. Fig. 13. thus holding the screen and the other the plate—thescreen, instead of resting directly on the bars, is heldin clips attached to them. In the earlv forms of thisholder these clips were attached to a sliding bar, which,when pushed one way or the other, altered the distanceof the screen. The disadvantage was that either twoor four corners had to be shifted separately and it wasnot easy to get the screen quite parallel, whilst theadjustment could only be done when the slide wasopen and apart from the camera. 46 THE HALF-TONE PROCESS. Penrose and Co. improved on the idea by intro-ducing a holder in which the screen was adjusted by turning one knob on theoutside of the holder, andthe distance moved wasshown by a pointer workingagainst an ivory scale forms of this holderare made, one comprisingthe smaller sizes from 6J x4 J up to 10 x 8, withordinary carriers for dryplate work; and the otheron Levys principle, withthe double pair of bars, for wet plate work, from12 x io
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Keywords: ., bookcentury1900, bookdecade1900, bookidhalftoneproc, bookyear1904
