(9) Paper prepared so that a brass pointer leaves a black mark on it. Dissolve 1/4 oz. pure sodium sulphide and 1/2 oz. sodium hyposulphite in 1 qt. rain water; filter the solution, and with it uniformly moisten the surface of the paper; then dry the latter under pressure between clean blotting paper.

(10) Tilhet's process. The paper upon which the design is to be reproduced, in order to prepare a negative copy, is first passed through a bath composed of 30 oz. white soap, 30 oz. alum, 40 oz. Flanders glue, 10 oz. white of eggs or albumen beaten up, 2 oz. glacial acetic acid, 10 oz. alcohol at 60°, 500 oz. water. The paper, after having been removed from this bath, is passed through a second bath composed of 50 oz. burnt umber, ground in alcohol, 20 oz. black pigment, 10 oz. Flanders glue, 500 oz. water, 10 oz. bichromate of potash. The paper having been thus. treated, must be kept when dry in a dark place. In order to prepare positive paper for the prints, a bath is used similar to the last, but without the umber, for which black pigment is substituted. To obtain coloured proofs instead of black ones, the black pigment is replaced by a pigment of any desired colour. To prepare the copies, the design or drawing is placed in an ordinary photographic printing-frame, the back of the design being next to the glass, and a sheet of negative paper prepared in the way first described is placed in contact with it. The frame is then exposed to light, 2 minutes' exposure being sufficient in good weather.

The sensitive paper is then removed from the frame in a dark place and is placed in water, when the design becomes visible in white, and the paper is allowed to dry. In order to obtain positive pictures from the negative thus prepared, the latter is placed in the printing-frame with a sheet of the positive paper prepared in the manner above described in contact with it, and after exposure to light for a sufficient time (about 2 minutes), the positive paper is removed in a dark place, and is plunged into water, which removes the part of the pigment which has not been affected by the light, without its being necessary to touch it. Any number of copies of the design or drawing may be produced upon any kind of paper, and in any colour or colours. The proportions of the different materials used to prepare the baths may be varied to suit circumstances, such as the weather, and the character of the design or of the paper.

(11) Zuccato's "papyrograph." A sheet of fine paper is saturated with a resinous varnish, and dried. On it, writing is made with an ink consisting of a strong solution of caustic aoda, slightly coloured in order to be more obvious to the eye. The soda immediately attacks the resinous preparation of the paper, converting it into a soap. The sheet is floated on water, written side upwards; the water soon penetrates the softened parts, making the written lines stand up in bold relief as ridges of fluid. The paper is removed from the surface of the water, and pressed between folds of blotting-paper, after which it is once more floated on the surface of the water, and again blotted off, in order to remove the remainder of the resin soap. The sheet thus prepared forms a stencil, of which the general ground is impervious to moisture, while the written lines, being denuded of varnish, are quite porous, and afford an easy passage to an aqueous liquid. In the early days of papyrograph printing, a pad, saturated with persulphate of iron, was placed at the back of the stencil, while the paper to be printed on was moistened with a solution of ferrocyanide of potassium.

The iron salt being forced through the porous lines by a gentle pressure, re-acted on the ferrocyanide; a blue impression was the result. It is now, however, found to be more convenient to print from the stencil by means of an aniline colour dissolved in glycerine, and the colouring power of this kind of ink is so great that dry paper may be used for receiving the impression. On a velvet pad which has been moistened with a solution of aniline blue in glycerine, is laid the paper stencil, this having been previously brushed over at the back with a little of the ink. It is now merely necessary to place sheets of paper on the upper face of the stencil, and to apply gentle pressure by means of an ordinary copying-press, in order to obtain copies rapidly and easily. About 600 copies can generally be taken from one stencil.

(12) Pumphrey's "collograph" depends on the fact that when a film of moist bichromated gelatine is brought into contact with ferrous salts, tannin, or certain other substances, the gelatine is so far altered as to acquire the property of attracting a fatty ink. Pum-phrey supplies plates of slate or glass covered on one side with a thin film of gelatine, and these are prepared for use by being soaked in a weak solution of potassium bichromate, all excess of moisture being then removed by first wiping with a cloth, and afterwards rolling 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. The original being removed, the plate is inked by means of a roller, moistened by a sponge, 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.

(13) Some methods 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 this nature; but these processes, which are capable of yielding 30 to 60 fairly good copies, depend on the use of a solution of an aniline colour for writing. In the case of copying processes introduced by Pumphrey and Byford, the writing is executed with a strong solution of an auiline 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 same 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.