Another method of multiplying and reversing negatives is first to print, from the negative, st carbon positive on glass, and from this, print reversed negatives with carbon-tissue. Negatives may also be enlarged and reversed hy taking a transparency from the original negative, through the camera, using either wet collodion or a gelatine dry plate. When a print is obtained on carbon-tissuc from a reversed negative, it is damped in cold water, and laid face downwards on a sheet of thin transfer-paper. The paper is first laid upon a sheet of glass, the sqneegee is then passed over the back of the tissue, and perfect contact is effected between tissue and paper. When squeegeeing, it is well first to cover the back of the tissue with a sheet of waterproof cloth. In about 20 minutes, the tissue and its support may he transferred to a tank of water, heated to about 35° (95° F.). The original paper on which the tissue was made will soon lift at the edges, and come away, leaving the film on the transfer-paper. All the parts unaffected by light will dissolve off, and by moving the print about, the picture will soon appear. Development must be continued until all the details of the picture are fully out, when the print may be finally washed by changing the water, and plunged into a bath of 1 oz. alum and 4 oz. water. It may then be hung up to dry. The object of placing a safe edge round the negative is to secure the perfect adhesion of the film to its support when developing. Were there no such margin, and the picture printed up to the edge of the negative, the tissue would curl up, and leave the transfer paper. Should the print be over-exposed, warmer water should be used in development ; if under exposed, colder water.
Double Transfer Process.—Ordinary—not reversed—negatives sre required for the double-transfer process. Here a waxed and collodionized glass plate takes the place of the transfer-paper employed in the method just described. A plate of glass of the finest quality should be selected, and coated with a solution of 20 gr. pure bees'-wax and 30 oz. pure benzol. The plate is levelled, and the solution is spread over the surface with a broad soft brush ; then drained off, and polished with a piece of old silk, taking care not to remove too much of the wax.
Coat the plate with plain collodion, and when the film has set, plunge into a bath of cold water, and wash until the film is uniformly wet. The exposed tissue having been damped and rendered pliable, may be squeegeed down to the collodion. When this is being done, the plate should be well oriered with water, and the tissue, bent up at the ends, he laid down first in the middle, and steadily lowered to the sides. After the lapse of 15 minutes, the print may be developed on its glass support.
Suitable transfer-paper is easily procured from the Autotype Co., of London, or other makers. This paper (which is enamelled) should be soaked in cold water for hour., or until it becomes soft. Transfer the paper to a bath of water heated to 49° (120° F.). When the surface becomes slimy,
the glass transparency and support are dipped into cold water, and the transfer-paper is laid down on its surface. It is next covered with waterproof cloth, and squeegeed into close contact. When dry, by passing a knife round the edge, the picture may be lifted from the glass, aud will have a highly polished surface. In order to retain the full brilliancy of the print, it should be mounted hy first trimming the edges of the picture on the glass plate, coated with warm starch or dextrine. Thin cardboard or white paper, after being damped, is laid over the back, and squeegeed down. Two or three thicknesses may be superposed, each being coated with starch. The print with its backing is then allowed to dry, after which, it may be removed from the glass support. The glaze may be retained by trimming the print after it has left the glass plate, and coating its edges only with hot starch, and, after mounting, placing it under pressure until dry.
Double transfer may be effected by using zinc plates, or ground-glass plates, by coating with wax, and omitting the collodion film.
Polished zinc imparts a glazed surface to the print, whereas ground-glass yields mat prints.
A flexible support for double transfer has been patented hy J. R. Sawyer, and is supplied by the Autotype Co., of London. It is coated with gelatine rendered insoluble by means of alum.
The support requires to be wEtxed, and the prints dealt with in detail, in much the same way as in the methods already described.
Tlze Woodbury Process.—The Woodbury process, like the carbon process, is based upon the action of light upon gelatine charged with potassium hichromate.
A solution of gelatine, prepared with a slight admixture of Indian-ink and potassium bichromate, is spread upon a plate of glass, and dried. When dry, the gelatine fllni is removed from the glass, printed, and developed, as in the carbon process. By this means, a relief is obtained. This is laid upon a perfectly flat, polished, and bard-tempered plate of steel. A plate of type-metal is then lnid upon the relief, and the whole is passed between the parallel jaws of a hydraulic engine. When taken from the press, it will be found that the type-metal is impressed with a perfect reverse, or intaglio, of the relief. In other words, the leaden plate has taken the true level of the steel, the divergs uce from the level surface is caused by the relief, the lights of the picture being represented by the highest relief, and the shadows by the depressions in the plate.
The success of the process hinges upon the steel plate being perfectly level, and on the SRMO conditions being ohserved in the construction of the press for subsequent printing. In the Wood bury photographic press, a sheet of thick plate-glass is laid upon the leaden intaglio, and the upper iron plate of the press, covered with hot cenaent, is let down upon the glass, which adheres to the cement.