. The book of photography; practical, theoretical and applied. 7.—Wooden COLLOTyPE Pkess. being more insoluble, will require muchlonger treatment. If left long, however,the plate will absorb too much moisture,yielding a grey, flat print. It is best,therefore, to allow the solution to remainfor, say, half an hour, and then to mop itoff with a sponge. The plate is now verygently dabbed with a soft, dry rag until itis perfectly clean, and it is then inked the etching is seen to be insufficient,the ink can be washed off with turpentine,and another etch given. The etchingsolution may be used
. The book of photography; practical, theoretical and applied. 7.—Wooden COLLOTyPE Pkess. being more insoluble, will require muchlonger treatment. If left long, however,the plate will absorb too much moisture,yielding a grey, flat print. It is best,therefore, to allow the solution to remainfor, say, half an hour, and then to mop itoff with a sponge. The plate is now verygently dabbed with a soft, dry rag until itis perfectly clean, and it is then inked the etching is seen to be insufficient,the ink can be washed off with turpentine,and another etch given. The etchingsolution may be used repeatedly. Machines and Presses. Before treating of the inking process itwill be advisable to devote some atten-tion to the different patterns of printingpresses and machines specially made forthis class of work. For experimentalattempts a letter-copying press will givegood results; but for any quantity ofwork a proper collotype printing machineis indispensable. Of these presses ormachines there are many patterns, fromthe simple wooden press shown by Fig. 888.—Collotype 1ress, working with Kollek AND ECCENTKIC. 887, which, however, is thoroughly satis-factoiy in operation, to the mostelaborate power-driven cylinder 888 illustrates a useful type ofpress working with a steel roller andeccentric. The selection of machineryof this description is so largely a matterof taste and of individual requirements,that it may safely be left to the workerhimself, who is hardly likely to purchaseexpensive plant, adapted only for largequantities of work, until he has gainedsome little experience of collotype print-ing in its simpler aspects. When that hasbeen acquired, the advice of a firm of 682 THE BOOK OF PHOTOGRAPHY. repute may be safely considered, after apersonal examination of the relativemerits of various machines. Tnking-up. Before placing the plate in the pressit should be carefully ascertained that theback is perfectly clean and free from grit,or there will be
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