Once the drawing has been traced sufficiently, the transfer paper must be coated very lightly and evenly with red chalk. Then it is fastened to the stone with wax and all the lines are traced under moderate pressure with a well-polished needle whose point is not sharp but rounded. Where the needle presses the tracing-paper, the color that is on the other side will take hold of the stone and thus transfer the drawing to it. If the needle is too sharp, it will injure the paper, and often the stone and the etching surface. The color on the paper must be rubbed off very carefully with a soft rag. If it is too thick, it will transfer itself coarsely to the stone. The red chalk may be put on the side of the paper that has the drawing on it, or on the reverse. This is decided according as the picture is to be on the stone in the same position as the original or reversed. If the impression is to be like the original, the drawing on the stone must be reversed; therefore in that case the tracing-paper is coated on the same side as the drawing. This side is laid on the stone, and the picture, which shows through, is traced.
In some cases it is good to transfer the drawing from the tracing immediately to the stone without tracing it with the needle. In this case, the paper is not coated with red chalk. The paper is merely laid on the prepared stone, drawing face down, and put through the press. If the drawing has been made with the chemical transfer ink, blackened with lampblack or colored with vermilion according to need, it will transfer itself to the stone. This will occur also in the case of a clean stone prepared for pen drawing if the drawing is made with lead pencil or with red chalk, wet or dry. Even the ordinary ink made from nutgall and vitriol of iron will transfer if it contains a little sugar or gum, but the paper must be well dampened and good pressure must be applied to the press.
In the pen-drawing process, the stone must be cleansed of possible surplus of color after the transfer. This is done by light rubbing with sand. It is not necessary in other processes. Any surplus of color that may have fixed itself to the stone is removed by gentle dusting with a soft brush.
II
WASTE PAPER
This is used partly for cleansing plates, partly and chiefly as underlay in printing.
If sheets are to be printed on both sides, usually a little of the first impression off-sets on the underlay paper, and if it were used again at once, it would off-set on the next impression. Therefore a fresh underlay paper must be used for each impression of the second side.
This must not be coarse, for fear of causing unevenness or holes in the leather in the printing-frame or in the so-called scraper-wood that makes the impression. A good quantity of this must be on hand, that fresh paper may always be available while the used paper is drying again. Each sheet that has been used should be hung up at once, and not more than three or four sheets should be hung over each other, to facilitate the drying. A special appliance is needed for this as well as for drying the impressions. A number of slats are fastened to the ceiling, leaving a space under it of about two feet, and about one foot distant from each other; and the sheets are hung on these with a pole made for the purpose, such as may be seen in any printery.
III
PRINTING-PAPER
Not all kinds of paper are equally good for lithography. On the whole, however, it may be assumed that this form of printing is very similar to copper-printing and book-printing, and that the paper that is good for these branches is suitable also for the stone, if only it does not contain too many impurities, grains of sand and other substances that make any considerable roughnesses. Such roughnesses, if considerable, have an ill effect not only on the impression, but chiefly on the leather in the printing frame. If the scraper is of wood, the leather will suffer less, but there will be caused grooves in the scraper that must be planed out again, because otherwise each following impression will show a more or less plain streak. If the scraper is of metal, the leather may tear or the stone itself may be injured if the foreign substance in the paper is very hard. Therefore it is well to hold the paper to the light before dampening or printing and to remove any apparent defect of magnitude with a little knife.