ROUTING.
This operation consists of cutting out pieces of metal or making hollows, where the block is required to print white ; as in catalogue illustrations, trimming round vignettes, etc. This is done on a small scale with chipping tools, 'punches, and a jig or fret-saw. In large firms, however, a routing machine is employed, having a drill-like cutter which revolves at a high speed. The cutter may be either fixed, or attached to a " universally " movable arm ; the latter plan being, of course, the most convenient. A typical router of the second description is shown by Fig. 917. Various kinds of cutters and drills are used which, as a rule, require sharpening on the edge only, a fine oilstone being employed for the purpose. When grind ing is required, a wooden handle is neces sary to hold the cutter.
PRoUNG.
It is better to take the final proof before mounting. The plate is laid in the press on an iron block to bring it up to type level, first cleaning it with turpentine and a soft rag, and seeing that there is no grit on the back. Stiff blue-black ink should be used, well rolled in with a composition roller. Smooth paper of good quality is necessary to obtain the best results. Several sheets of stout paper and a piece of thick indiarubber sheeting or of printers' " blanket " are laid over the Proof sheet, and a strong pressure applied for a few seconds. On examining the re
sult, it may be found that the shadows print too heavily, or that the contrast is unsatisfactory. In either case, what is called an underlay has to be cut from the proof to the shape of the portions it is desired to modify, this being pasted to the back of the plate. Sometimes several layers of underlay may be necessary, each layer being cut a trifle smaller than the preceding one, and the edges scraped so as to taper down. This is particularly requisite in the ease of vignettes. An overlay placed above the proof sheet may also be needed. This is cut or built up in a similar fashion to the underlay, and is of convex form. Various methods have been suggested for making the overlay or underlay, among others being an ingenious system of obtaining a relief image in bichromated gelatine from the negative used in making the block. The De Vinne Bierstadt overlay shown at the Print ing Trades Exhibition, at the Royal Agri cultural Hall, London, appears to be based on a similar process.