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Polygraphic Copying Processes

A NUMBER of processes for reproducing letters, maps, drawings, &c., have, at various times, been devised. The most perfect is the lithographic process which depends for its efficiency on the repellent action of water on a greasy surface. The lithographic process is briefly as follows. The writing or design is formed with a special ink on a special paper. It is then transferred to a lithographic stone by pressure, the whole of the paper being removed by a damp sponge, leaving the design upon the stone. This is now wetted with water, and rolled with printers' ink, the latter attaching itself only to the lines forming the design and being repelled by the water held in the pores of the stone. Clean paper is now laid upon the stone, and the whole is pulled through the press, the stone receiving a fresh supply of ink from the roller for each impression required.

The process is as good of its kind as it could be, and in the hands of a skilled lithographer leaves nothing to be desired. But every one does not own a press, nor would every one be disposed to go to the expense and trouble which it involves. It therefore becomes desirable to adopt some process requiring less care and less plant. The most simple perhaps is the use of a copying ink, which consists of ordinary ink, rendered sticky with sugar or other substances, but the impression from such a source is of course reversed, and must be made upon thin paper, so that the lines can be read through it. This process is in common use in most offices where it is customary to keep in a letter-book a copy of each document daily sent to the post. With the best copying inks hardly more than six copies can be impressed without the seventh becoming almost or quite illegible. Hence inventors have striven to find some means of obtaining rapidly and easily copies of letters, &c., which shall not deteriorate in quality as their quantity increases.

Mr. Edison, who seems ever at the fore with some contrivance or other, to benefit his fellows, has invented a most ingenious electric pen. This pen is really a little magnetic engine which moves a piercer rapidly up and down as it is drawn over the paper, making a succession of tiny holes. The stencil so obtained is treated with ink, and will serve for many hundred copies. A like end is attained by the "horograph," in which the stiletto is worked by clockwork in lieu of electricity. In another process the writing is effected with a pointed pen, and the paper is placed upon a metallic file-like surface, so that the characters are rubbed into the paper in the form of minute ragged holes. In all these three systems the resulting copies show signs of the manner in which they have been originated, for the lines consist of series of dots. It is evident that such copies cannot give the fac-simile reproduction of a man's handwriting; for the up and down strokes are reduced to one common representation. Neither can they reproduce the touch of an artist, and for the same reason. A process with comes nearer this goal is the "papyrograph." In this process the characters are written with caustic alkali, on varnished paper. The ink decomposes the resin in the varnish, forming soap, which is dissolved out by the application of water. This leaves a kind of filled-up but porous stencil. The ink, consisting of an aniline dye, is applied to a velvet pad. This is pressed against the stencil, and the liquid is forced through the porous characters on to the paper placed beneath it. Although this last gives good results, the copies show evidence of having been produced by mechanical means, and it also has the disadvantage of employing both ink and paper which writers are not accustomed to use, and which more or less distort the figures which they make. The new gelatine process, which has lately been brought out under all kinds of different names, has none of these disadvantages. It is called the chromograph, the hektograph, and multigraph, and many other graphs, too numerous to mention. An American gentleman has lately brought out another which he christens the "lick-em-allograph," but whether it bears out this description we have had no means of judging. However, whatever be the name which they individually bear,they all in reality represent one and the same thing.

A zinc tray is filled with a gelatinous mixture which serves as does the stone in the lithographic process for holding the design. The latter is traced upon ordinary paper with an ordinary pen, but a special ink is employed. When the design is completed it is laid face downward on the gelatinous surface, and gently smoothed on the back by the hand, no press being required at this or any other stage of the process. After a few seconds the paper is gradually pulled away, when the design is seen to be cleanly and sharply detailed upon the preparation. Clean paper is now pressed upon this transferred design, and as many as fifty or sixty perfect copies can be rapidly and easily secured. By the following directions the entire apparatus can be made for very small sum. A piece of zinc large enough to receive a whole sheet of note-paper will cost about fourpence, it should measure 11 inches by 9. The sides can easily be bent over for half an inch all round so as to form a tray, and the corners should each receive a little treatment with gummed paper, so as to prevent the composition leaking through while it is in the fluid state. To make the preparation, take four ounces of common gelatine or good glue, and soak it for some hours in eight ounces of cold water, until it is perfectly flaccid. Now heat it in a water-bath, that is to say, place the vessel in which it has been mixed into a saucepan containing water, and place this on the fire or other source of heat until its contents are quite fluid. Now add sixteen ounces of glycerine. The mixture must be thoroughly stirred and incorporated, after which it must be poured out into the zinc tray to set. The tray should be placed as level as possible, and in some cool place where it will not be disturbed, and where it will be free from dust. In a few hours, according to the temperature, it will be ready for use, but before the first design is pressed upon it, the surface should be sponged with water, and carefully wiped with a clean cloth. The design can be removed by sponging with tepid water, when the gelatine will be ready to receive a fresh one without further treatment.