Copying is a term in general use for a great many different processes, but 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 tracing-paper (which may be bought at any stationer's) 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 clean paper on which the copy is to be made; the traced lines are gone over with a hard point, and thus indicated faintly on the paper. Guided by the traced lines, the copy can then be drawn in. It is usual to have the ruddle or black lead on a separate piece of thin paper, and interposed between the tracing and the paper. When the copy is required of a different size from the original, the simplest way is to sketch it by 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; a piece of paper for the copy is prepared with a corresponding number of squares, of a smaller or larger size, according 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 comparatively 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. If it is not convenient to cover the original drawing with pencil lines, or to tie threads over the face of it, a very good way is to draw the squares on a piece of tracing-paper, and put that over the original; the same tracing-paper will do any number of drawings. A pair of proportional compasses (see COMPASSES) will be found very useful for fixing the proportional size of the squares. Any drawing consisting principally of straight lines, such as a plan, can be conveniently reduced by constructing a scale to snit the reduced size required. The lines of the original are measured by its scale, and the same proportion of the smaller scale gives the necessary measurement. The Pantograph (q.v.) is another means of making a reduction or enlargement, but is very seldom used now. It is only accurate 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 documents 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 modifications of this arrangement have been devised for producing a number of copies of circulars, &c. from one written copy, and are known as 'graphs' (hektograph, &c.). A document written with the ink prepared for the purpose is transferred by pressure with the hand to a gelatinous slab, from which as many as fifty or sixty 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. Carbonised paper is put between two or three or more sheets of thin paper ('flimsy'), and thus, whatever is written on the top sheet by a hardish pencil is duplicated on the others. When an indefinite number of copies of any drawing or other subject is required, there are many printing processes which may be employed. Letters or circulars, if written with lithographic ink, can be transferred to stone, and any number printed. Engineers' or architects' drawings, or any other drawing executed in line, can be very successfully reproduced in any size by the photo-lithograph process, which will be described under LITHOGRAPHY. If required for block or letterpress printing, then any of the zincotype processes may be employed. By this process, also, plates to reprint steel-engravings can be produced from any printed engraving (see ENGRAVING). For reproducing drawings executed otherwise than in line, photographs from nature, or paintings, there are many processes which will also be described in the same article.
Copying in photography, that is, the method of copying pictures and other drawings by the camera, will be described under PHOTOGRAPHY.
Drawings for wood-engravings are now seldom made directly on the wood, but executed on paper or cardboard, and copied by photography on to the wood. By this means the drawing need not be so minute as the required engraving, but may be of any convenient size. The process employed will also be described under PHOTOGRAPHY.