In reproducing the image to be printed by any make of litho graphic hand-press the principle involved is the same—that of the scraper being forced across the plate. This scraper, no matter what kind of wood it is made from, must be perfectly straight and the face, which is V-shaped, must he carefully rounded so that it will not sag or bulge when pressure is applied. The bed of the hand-press, upon which the stone that is to be printed from is placed, must be level and neither concaved nor convexed for, while the stone is not supposed to bend, a convexed bed will cause the stone to balance and move slightly with every impres sion, thus making it impossible to register impressions on it ; while a concaved bed will wear down the corners of the stone and put it out of plumb. More work has been spoiled by presses with uneven beds than in almost any other way.
In 1905 a new kind of lithographic press was invented in the United States called the "offset press." This was a steam-driven press, but it called for a hand-press to make the transfers to be used, and make them quickly and accurately. Several inventors started to make an offset hand-press. The first one offered re sembled a washing machine wringer. The proof was pulled from a stone, laid on another piece of transfer paper, and the two were run through this wringer-like machine. Some work was turned out this way, but as there were no guides to feed the sheets to, it was next to impossible to make a sheet register prop erly, so this proposition was abandoned and other designs taken up. Finally, an offset hand-press equipped with a large rubber covered cylinder was offered. This same principle has lasted to
the present day. This large rubber cylinder travels over the stone or plate containing the image from which it takes an im pression, and then it goes on to a bed upon which is laid the paper. As the cylinder goes over the paper the image is trans ferred from the rubber blanket to the paper and the work of printing is done, so far as the sheet is concerned.
It occasionally happens that one wishes to pull a transfer of a piece of copper plate engraved work to use on a lithographic hand-press. From a purely mechanical point of view the con struction of the copper plate press is an exceedingly simple matter. Its purpose is to produce a heavy and uniform pressure on the plate during the operation. To make a lithographic trans fer from a copper plate engraving one should lay the plate face upward on the bed of the press, lay the paper on it and pass it between the two iron cylinders.
The material used in making lithographic transfers from copper plate engravings consists of transfer ink, whiting, transfer paper and a good supply of clean rags. The copper plate is first heated, but not enough to burn the ink; then the transfer ink is forced into the engraved parts until every part is fully charged. In cleaning the plate it should be carefully rubbed with a rag charged with whiting until all the surplus ink is removed. The transfer paper to be used is dampened—or commercial transfer paper may be used which is made to retain dampness—and the plate and paper used before the plate gets cold. Transfers made in this way may be used in lithographing on a hand-press.