Another class of printing stencil is made by the mechanical perforation of imitable paper or tissue. Stencils perforated by a rapidly rising and falling needle-point, actuated by a treadle, have long been used for the printing of embroidery patterns. In euch a case, powdered colour, mixed with resin, is dusted through the stencil, after which the device is fixed by the application of sufficient heat to soften the resin. Edison propoees to use such perforated stencils for ordinary autographic' printing purposes, and replaces the complex treadle perforating-machine by a kind of pen, in which a needle-point is mada to move rapidly up and down by means of a email electric motor attached to the instrument. When Edison'e electric pen is connected with a battery of two elements, the needle rapidly paeses in and out of the perforated point of the instrument. If written with on a piece of blank paper, the paper becomes perforated. The eheet of ink-proof paper having been written on with the electric pen, can be need as a printing etencil by merely laying it down on a sheet of white paper and paeeing an inking-roller over its back. The operation of printing ill very rapid, so that many copies can be produced in a ehort time. Other perforating pens have followed in the wake of Edison's eketric inetrnment, among which may be mentioned the "horograph," very convenient and portable clockwork pen, manufactured by Newton, Wilson, & Co.,of Cheapside. A pneumatic; pen, in which the motive power is a stream of air eupplied from a foot-bellowe, has also been introduced into the market. A still more complex and expensive arrangement than either of the preceding, for producing perforated etencile, consists of an induction coil, capable of giving a eufficiently powerful spark to perforate the eteneil -paper ; and this spark is made to continually pass between a partially insulated metallic pen and a metallic plate, on which the stencil-paper is laid.
All these perforating arrangements have the disadvantages of being expeneive, complex in oonetruetion, and liable to get out of order when used by unskilled persons, while the ;perpendicular poeition in which the mechanical perforating pens must be held, necessarily hampere the freedom of the writer. In a new perforating method recently introduced by Zuccato, the impen ions stencil-paper ie laid on a hardened steel plate, cut on the face like a fine file, and the writing is executed by means of a point or etyle of hardened steel. Under these circumstances, the teeth of the file-like plate perforate tho paper wherever the point of the style exerts pressum and a. stencil eminently adapted for printing t'rom is tho reault. This kind of printing is called " trypo graph." A sheet of tho prepared paper is laid on the file-like plate and written upon with the hardened eteel pencil, the operation of writing being as easy as if a pencil wore employed. By fixing the stencil on the frame of a desk-like press, placing a eheet of white paper underneath, and then pushing over the upper eurfaco of the stencil an indiarubber scraper or squeegee charged with printing-ink, the ink passing through the perforation produces a copy of the original writing. As mnny as 6000 copies can be obtained from one stencil. Thin metallic plates are readily perforated by Zuceato's method, and calico receives the trypographic impression admirably.
Puniphrey's "collograph" depends on the fact that when a film of moist bichromated gelatine is brought into contact with ferrous ealts, tannin, or certain other substance°, the gelatine is so far altered as to acquire the property of attracting a fatty ink. Pumphrey supplies plates of slate or glass covered on one side with a thin film of gelatine, and these are prepared tbr use by being soaked in a weak solution of potassium bichromate, all excese of moisture being then removed by firet wiping with a cloth, and afterwards rolliog paper on the damp surface. A drawing or
writing, which has been made with either an ordinary iron and gall-nut ink, or with a special ink, is transferred to the prepared plate, just as in the case of the transfer to zinc. Tho original being removed, the plate is inked by means of a roller, moistened by a eponge, in order to remove any trace of ink from the ground, and then printed from, much as if it were a lithographic stone, or a zincographic plate.
There aro eome methode, which are rather copying than printing processee, as they depend on the writing of an original with a very intense ink, and then dividing the ink, so as to obtain a. number of feebler copies. The ordinary method of obtaining one or two reverse copies of a letter on thin paper is of thie nature ; but these processes, which are capable of yielding 30-60 fairly good copies, depend on the use of a solution of an aniline colour for wiiting. In the case of copying processes introduced by Pumphrcy and Byford, the writing is executed with a strong solution of an aniline colour on thin, and tolerably hard, paper. The writing quite penetrates the thin paper, and on pressing a sheet of moistened paper against the back of the original, some of the aniline colour will set off on the damp paper, giving a direct copy of the original writing. In the smuu way, numerous copies may be produced; but processes of this kind cannot reproduce very fine lines with distinctness. A somewhat analogous arrangement for obtaining numerous copies is afforded by Waterlow's " multiplex copying portfolio" and its contents. The writing is done with the aniline ink, and a damp sheet of very soft and porous paper is pressed down on the writing. This soft paper absorbs a large proportion of the aniline ink, and itself forms a reversed printing surface, capable of yielding a considerable number of direct copies to damp sheets of paper.
The just-described copying processes labour under the disadvantage of requiring the use of damp paper for receiving the impression ; but this difficulty has been overcome in an arrangement which has been introduced under the names of " hectograph " and " chrnmograph," these differing from each other rather as regards detail than kind. The writing is executed on ordinary writing paper with an aniline ink, and when the lines have dried, the original is transferred to the surface of a slab of soft gelatinous composition, analogous to that used for making printers' millers, contact being established by a gentle rubbing with the hand. The original, after being allowed to remain in contact with the gelatine slab for about two minutes, is stripped off, leaving the greater part of the ink on the gelatine. To obtain the copies, it is now merely necessary to lay paper on the slab, and either rub down with the hand, or establish contact by means of a soft roller. The requisite number of copies having been obtained, or the colnur on the lines being exhausted, the slab can be cleaned by means of a damp sponge, when it is again ready for W30. A composition for making the slab may be prepared as follows :-1 lb. of gelatine is soaked in water until it becomes flaccid, after which it is melted, in a water-bath, with 6 lb. of common glycerine, the heat being maintained for a few hours so as to drive off all excess of water. The mixture is then poured out into zinc trays in. deep, and allowed to set. The ink may be prepared by dissolving one part of aniline violet (blue shade) in a mixture of seven parts of water and one of alcohol. Letters written in coloured inks will give 150 copies, and in special black ink, 50 copies. The process is also known is the " Vienna multicopyist." Another composition for the slab consists of 130 parts water, 75 sulphate of baryta, 30 gelatine, 30 sugar, 180 glycerine.