MACHINES AND P RESSES.
Before treating of the inking process it will be advisable to devote some atten tion to the different patterns of printing presses and machines specially made for this class of work. For experimental attempts a letter-copying press will give good results: but for any quantity of work a proper collotype printing machine is indispensable. Of these presses or machines there are many patterns, from the simple wooden press shown by Fig.
being more insoluble, will require much longer 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 remain for, say, half an hour, and then to mop it off with a sponge. The plate is now very gently dabbed with a soft, dry rag until it is perfectly clean, and it is then inked up. If the etching is seen to be insufficient, the ink can be washed off with turpentine, and another etch given. The etching
solution may be used repeatedly.
887, which, however, is thoroughly satis factory in operation, to the most elaborate power-driven cylinder machines. Fig. 888 illustrates a useful type of press working with a steel roller and eccentric. The selection of machinery of this description is so largely a matter of taste and of individual requirements, that it may safely be left to the worker himself, who is hardly likely to purchase expensive plant, adapted only for large quantities of work, until he has gained some little experience of collotype print ing in its simpler aspects. When that has been acquired, the advice of a firm of repute may be safely considered, after a personal examination of the relative merits of various machines.