(14) Hectograph or Chromograph. This process obviates the necessity for using damp paper to receive the impression. The writing is executed on ordinary writing-paper with 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' rollers, contact being established by gentle rubbing with the hand. The original, after being allowed to remain in contact with the gelatine slab for about 2 minutes, is stripped off, leaving the greater part of the ink on the gelatine. To obtain copies, it is merely necessary to lay paper on the slab, and rub down with the hand or a soft pad. When the requisite number of copies is obtained, or the lines are effaced, the slab can be cleaned with a damp sponge, and is again ready for use. The composition for the slab may be prepared thus: - 1 lb. gelatine (or l 1/2lb. glue) is soaked in water till it becomes flaccid, after which it is melted in a water-bath with 6 lb. common glycerine, the heat being maintained for a few hours to drive off all excess of water. The mixture is poured into zinc trays } in. deep, and allowed to set. Another composition is 130 parts water, 75 baryta sulphate, 30 gelatine, 30 sugar. 180 glycerine.
(15) Magne has introduced an ink or pencil possessed of such qualities that a writing or drawing made with it, when dry, can be covered with a fatty ink, and the paper being saturated with a suitable liquid, it can be completely copied without being injured itself. Common printing ink acts towards this saturating fluid in the same way as Magne's pencil, so that printed matter and cuts can be reproduced. The liquid employed to saturate the paper consists of 15 oz. acid (sulphuric is the best) and 35 oz. alcohol. If intended for autographic reproduction, 100 oz. water should be added. The proportions may be varied, but to prevent injury to the original, there must be plenty of alcohol. Autographs for reproduction must be written with ink or pencil, of such composition that they can take up the fatty ink; the same kind is used for all kinds of paper, whether sized or not. The portions of the paper not covered with ink are protected against the lithographic ink by an acid composition which repels the greasy ink, does not attack the cellulose, and, therefore, leaves the original perfectly unchanged. The ink consists of proteine substances (albumen, caseine, fibrine, &c), and of bichromated salts, alum, cyanides, etc.
In making it there is dissolved a quantity of water 2 or 3 times as great as that of the albumen or other proteine substance, a mixture of 2 parts of a bichromate or alum, and 1 of prussiate of potash. A certain quantity of albumen is also beaten up with an equal weight of water. The proportion of salts to that of albumen is about as 6 to 100. The two liquids are mixed intimately, and a suitable quantity of pigment is added. The ink, which must have pretty deep colour, is unchangeable, remains thin and fluid, and can be used with a pen, pencil, or drawing pen, on any kind of paper, except very heavy paste-board or too thin silk paper. Pencils or crayons used in this process consist chiefly of paraffin coloured with very fine lamp-black or ivory-black, or with any other very finely - powdered pigment for other colours. When lamp-black is used, the proportions are, 16 oz. lamp-black to 100 oz. paraffin. To make pencils of different hardness, the paraffin is melted and ~the colour added, and then a certain quantity of ordinary rosin (colophony) is added, usually not over 10 per cent. The mass is cast into candle moulds when in a semi-liquid state, and taken out when cold. These cylinders are then cut in pieces and wrapped in strong paper, or covered with wood like common lead pencils.
The method of taking a copy of what has been written or drawn is as follows: If the work was done in ink, it is ready to copy as soon as dry. If in pencil, the drawing must be steamed a few seconds by holding it over a vessel of boiling water. After being air-dried, it is carefully floated, face upward, on the acidified alcoholic liquid. There it is left until thoroughly saturated, and then it is spread out on a sheet of glass or smooth board, and inked with an ordinary lithographic roller. All the letters and lines will be covered with the greasy ink. As soon as sufficiently inked, it is carefully pressed with a damp sponge on those places that have taken the ink, and then washed with water. To remove the excess of moisture, it is spread out on a plate of plaster-of-Paris, and then transferred to a stone or zinc plate, and the copy taken. The precautions necessary in order to preserve the original copy are to wash it with carbonate of ammonia, or of soda, rinsing with cold water, removing the excess of water on a plate of gypsum or blotting-paper, and then drying it in the press between sheets of porous paper.
To reproduce anything printed with printers' ink, the following method is pursued: - The mixture of alcohol and acid is applied either to the face or back of the print with a brush. The liquid instantly penetrates the paper; the surface is then quickly washed off and the sheet carefully spread out on a damped plate of glass or wood. There it is inked with an ordinary lithographic ink roller, gently washed to remove the excess of acid, dried' on the gypsum plate, put on the stone, and a sufficient pressure applied. The transfer of the negative is finished, and the ordinary lithographic process begins. If both sides of a drawing or manuscript are to be copied, both sides are blackened, one after the other, the operation being carried out on one side as far as the transfer to a stone, and then the other side is inked and transferred. When copies of printed matter are to be made, the negative is transferred to a polished zinc plate, and then etched in the usual manner with acids.