(2) It must be very transparent, like glass, so that the underlying drawing or painting can be seen perfectly.
(3) The ink or lead crayon used for copying must lie on it easily and plainly.
It is at its best if it is easy to work on it with a fine brush, using Chinese ink, or, (if the drawing is to be transferred directly to the stone), with the soft chemical ink described under the caption "[Transfer Ink]." Generally this can be done without further preparation in the case of most papers made transparent by oiling. Varnished paper, however, which is far more transparent, generally must be well washed with milk and dried again beforehand, that it may take the ink well and permit work with the finest strokes.
(4) Finally, a good tracing-paper must be very fine, pliable, tender and yet not in the least brittle. There is some very transparent varnished paper, but it breaks at the first attempt to bend it, so that it is hard to trace the drawing afterward on stone with the tracing-needle, because nearly every stroke tears the paper and the lines and outlines become coarse.
Very good transparent paper may be made as follows:—
Take the finest writing or vellum paper and soak it with nut or poppy oil, mixed with a little sugar of lead to make it dry more readily. When well soaked with oil, dry it a bit between waste paper and hang it up. Usually it is available in a few days. This paper is cheaper than the paper sold by stationers under the names of straw paper, etc., and about equally transparent. Still more transparent will it be if instead of the oil a varnish cooked from the oils is used. In this also the sugar of lead is an excellent drier. To make the varnish easier to manipulate and more readily penetrative for the paper, it may be thinned down with oil of turpentine. If it is desired to manufacture a greater quantity of this paper, one sheet is laid on another and painted with varnish. Then the whole mass is left for some time covered with a stone plate or a board, that the varnish may soak properly and evenly into all the sheets. Afterward the sheets are hung up singly to dry. The more varnish they have, the more transparent will they be; but too much is not good. Care must be taken that no drops of varnish adhere. It is best to brush the varnish evenly over each sheet before hanging it up.
Silk paper, such as is used in copper-printing to lay between impressions to prevent off-set, is still better for varnishing because it is finer. Only it must be very even and have no holes. The very greatest fineness of paper is desirable, for the reason that then the strokes made by the needle on the stone are fine and not coarse.
Instead of varnish made by boiling down nut or poppy oil, one can use Venetian turpentine, which merely has been thinned down with one half as much oil of turpentine. Such paper generally is dry enough after twenty-four hours. Too large a quantity must not be made at one time, because it becomes tough and brittle after a while.
Even with the most transparent paper it occurs that certain delicate drawings, and especially color pictures, will not show through sufficiently. Then the drawing must be fastened to a window pane to obtain added illumination. This manner of work is very uncomfortable, however, and the arms hurt one soon, so that it is necessary to stop. It is better to have a tracing-board made with a strong, clear pane of glass in the centre. Under it is a mirror so adjusted that it reflects light upward through the drawing.
It is understood, of course, that in tracing only the outlines are copied and not every stroke of shading, etc. Although the final work is greatly facilitated by the observation of the utmost care in tracing, the tracing of every little detail will merely make the work involved and perplexing. Practice must show the proper degree of exactness. A very good and skillful artist often needs only a few main outlines, to reproduce the original picture with the greatest accuracy.