. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. of air has to be drivenout before the vacuum is formed, and there is a con-siderable risk of leakage at the screwed joint. It is also possible to have two springy pieces of woodarranged to form a clamp when pressed open, and theplate inserted between. 104 THE HALF-TONE PROCESS. The Levy whirler, fig. 48, is a very good fixture forlarge plates. It is attached to the end of a swingingbracket, with the other end fixed to the wall. Thewhirling portion is pivoted on a horizontal axis, so that Fig
. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. of air has to be drivenout before the vacuum is formed, and there is a con-siderable risk of leakage at the screwed joint. It is also possible to have two springy pieces of woodarranged to form a clamp when pressed open, and theplate inserted between. 104 THE HALF-TONE PROCESS. The Levy whirler, fig. 48, is a very good fixture forlarge plates. It is attached to the end of a swingingbracket, with the other end fixed to the wall. Thewhirling portion is pivoted on a horizontal axis, so that Fig. 48. 49) embodies a very good the plate can be face up for coating, and then turnedface down for whirling. This form of whirler can befixed over a tub, as already described, and the swingingarm permits it to be swung from the tub over a stovefor drying off. The turntable whirler (fiiprinciple, but itsdisadvantages arethat as the platehas to be whirledface upwards it isliable to attractdust ; further, thatunless there is a Fig 49 guard round it there is a great deal of splashing about the room and. THE PRINTING ROOM. upon the operator ; also the plate cannot be quicklydetached. Its chief advantage is for large and heavyplates, and for lithographic stones when the latter areused for direct half-tone printing. When fitted insideof a circular iron box with a trough round to catch thesurplus solution, a small stove inside to dry the platewhilst being whirled, and a glass lid to keep out thedust, this form of whirler becomes very efficient, andthe author has seen such whirlers capable of taking aplate up to forty inches square. Most other whirlers in use are modifications of oneor other of these principles, and need not be particu-larly described. A gas stove of the ordinary circular pattern, but onethat will give a good spreading flame, is required nearthe whirler for drying off the plates. The gas connec-tion should have a tap for regulating the flame. If thefitting already exists
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