COPYING, a term in general use for a great many different processes, which may be described generally as the reproduction, usually either on an enlarged or reduced scale, of any drawing, map or other work of art. A few of the methods employed may be shortly described If the copy is to be the same size as the original, the easiest way is to trace it. A piece of trac ing-paper is put over the drawing, and the principal lines gone over with pencil. The back of the tracing is then rubbed with black lead or ruddle, and put on the paper on which the copy is to be made; the traced lines are gone over with a hard point, and thus indicated on the paper. Guided by the traced lines, the copy.can then be drawn in. When the copy is required of a different size from the original, the sim plest way is to sketch it ty hand and eye but where more mechanical accuracy is required, the method of squares is very useful. The original is covered with squares of any convenient size by pencil lines or threads or by tracing paper ruled off in squares; a piece of paper for the copy is prepared with a corresponding number of squares, of a smaller or larger size, accord ing as the copy is wanted smaller or larger. These squares must bear the same proportion to the squares on the original as the copy is to bear to the original. It is then a compara tively easy matter to copy in each square the part of the original in the corresponding square. To avoid confusion if the squares are small, it is well to number them along each side of the drawing. Any drawing consisting principally of straight lines, such as a plan, can be con veniently reduced by constructing a scale to suit the reduced size required. The lines of the original are measured by its scale, and the same proportion of the smaller scale gives the neces sary measurement. The pantograph is another means of making a reduction or enlargement, but is very seldom used now. It is only ac curate in a general way. Perhaps the simplest and most exact method is to get the original photographed to the required size; the copy can then be traced on to clean paper as already described.
The copying of letters and other docu ments for commercial purposes is usually done by means of the ordinary copying-press, which is so familiar in every counting-house as to need no detailed description. A letter written with specially prepared ink is transferred to another piece of paper by means of damp and pressure. Common ink thickened with a little sugar will serve as copying ink. Many modifi cations of this arrangement have been devised for producing a number of copies of circulars, etc., from one written copy, and are known as °graphs.° A document written with the ink prepared for the purpose is transferred by pres sure with the hand to a gelatinous slab, from which as many as 50 or 60 copies, more or less distinct, can be retransferred by rubbing with the hand. A very useful method of manifold writing is largely employed in telegraphic news work, and for duplicating invoices by retail tradesmen. Carbonized paper is put between two, three or more sheets of thin paper, and thus whatever is written on the top sheet with a hard pencil is duplicated on the others. When an indefinite number of copies or any drawing or other subject is required, there are many printing processes which may be em ployed. Letters or circulars, if written with lithographic ink, can be transferred to stone, and any number printed. Engineers' or archi tects' drawings, or any other drawing executed in line, can be very successfully reproduced in any size by the photo-lithographic process, which depends on the action of light on citrate of iron and prussiate of potash. (See PHO TOGRAPHY). If required for block or letterpress printing, then any of the zincotpye processes may be employed. By this process, also, plates to reprint steel-engravings can be produced from any printed engraving. For reproducing drawings executed otherwise than in line, pho tographs from nature, or paintings, there are many other processes.