The prints as soon as dry can be used for drawing on. On the grain papers the outline may be drawn with the pen and be shaded with chalk, or it may be drawn with chalk only. With unprepared papers it is advisable to coat them with a thin solution of boiled starch, as then the transfer to zinc or stone is most exact. The drawing may also be left a long time without spoiling. The coating is performed with a pad dipped into the liquid, which consists of one part of fine bookbinder’s starch and four or five parts of water, and passed several times over the print.
The drawings ought only to be done with greasy lithographic tusch or chalk or autographic ink, which consists principally of greasy materials and lampblack. For pen drawings hard pens should be used, and care must be taken to make thick strokes. Only a little tusch or ink ought to be taken into the pen, so that it does not run out, and thus clean, sharp lines be obtained. If this be observed very close shadings and cross lines can be produced clean and neat.
When the drawing is finished and the tusch or ink has become dry the same should be laid between damp blotting-paper, and meanwhile a clean ground, and dry pumiced stone worked in the press and the pressure correctly adjusted. As soon as the drawing has become moderately damp right through, and the paper feels soft without being wet, it should be laid with the image downwards on the stone and transferred to the same with strong pressure. After repeated working the paper will adhere firmly to the stone. In order to loosen it the stone should be covered with hot water of about 80° C., when the film will dissolve and the paper become quite free. Any exertion of force must in this {87} operation be quite avoided, and the paper must not be pulled off with violence. All, even the finest lines, will have been transferred to the stone. The stone is now gummed, if possible allowed to stand for some hours, and then etched with a gum etching solution of two degrees’ acid strength, or later etched in relief, and is ready for printing. If the transfer is made to zinc, for printing from this the plate is treated as suggested on p. [6.] If, however, a relief etching for the typographic press is to be prepared of the subject, the transfer is made on to a smooth polished zinc plate.
3. LITHOGRAVURE.
With this particular process an intaglio printing stone or intaglio printing plate is prepared by chemico-physical means.
This process was discovered and brought to great perfection by Chas. Eckstein, the general director of the Typographical Bureau at the Hague, and offers especially many advantages for the reproduction of maps.
A map engraved, drawn, or transferred on stone, or written in on copper, in originally one colour, can by this process in a comparatively easy way be converted into a many-coloured print; this process can also be used very advantageously for changing the names for the places—rivers, mountains, etc. In the first place intaglio original printing plates in all the colours can be prepared which can then be printed for further reproduction; in the second case it is necessary to re-engrave the network, hydrography, etc.
When it is desired to convert a monochrome image into a multi-coloured map, as many stones as there are colours to be used must be first ground and polished with oxalic acid till they have a high polish.
In the meantime an asphalt or other light-sensitive solution should be prepared, with which the stone is coated in the dark very evenly, and somewhat more than is done for a photo-lithographic print.
The asphalt solution is composed of—