The photographic news

• Bandzählung: 12.1868
• Erscheinungsdatum: 1868
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-186800009
• PURL: http://digital.slub-dresden.de/id1780948042-18680000
• OAI: oai:de:slub-dresden:db:id-1780948042-18680000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

JutY 24, 1868.J is etched, then covered with gum ; the required detail is scratched in witli the point; printing ink is then forced into the lines with a dabber made of closely rolled flannel, worked round and round till the lines are well charged. A sheet of waste piper is put over the plate, and a proof is pulled, which drives the ink wwll into the scratches, and also takes off most of the superfluous ink; the remainder is taken off by sponging the plate, when it comes off with the gum ; if necessary, the plate may be washed with turpentine an d then rolled in again. If the part to be altered is large, or the work has been on it for some time, it is better to grain it with a small muller and line sand, after treating it with sulphuric acid. If the part cannot well be grained, the acid must bo allowed to work for a longer time. Failures. I will now notice briefly the principal causes of failure in each part of the process. 1. P.-eparation of tin Transfers. The ink refuses to leave the ground of the print.—The paper has become too old and decomposed, or has been dried at too great a heat. The ne gative was not sufficiently intense, or the print over-exposed. The ink leaves the lines.—The print has not been suffi ciently exposed to light. The detail in those parts of the negative is clouded over, and hinders the action of light. Ink too soft. Pressure of sponge too great. This fault may sometimes be remedied by taking a little transfer ink on the forefinger and dabbing the lines with it. The lines ragged and broken.—Under-exposure. Coating of gelatine too thick. The washing water too hot. Surface of the paper spotted over.—The coat of gelatine too thin. The pressure too great when inking. Use a thicker coit of gelatine, or ink by hand. The close parts clogged with ink.—Too thin a coat of gelatine. Imperfect contact between the negative and paper. Over-exposure Excess of ink, too hard or too soft. 2. Transferring to 'Zinc. The ink does not leave the paper, or only transfers faintly.—This may arise from long soaking of the transfers in order to get the ink off. The zinc plate has been kept too long. Too little ink on the print. The transfer too old. The lines are much spread.—The ink is too soft. The cost of gelatine too thick. Excess of ink, resulting from over-exposure, or from too thick a coating being applied. The ink does not leave the print in parts.—Uneven pres sure while transferring. Uneven drying of the surface of the print after washing, which might be obviated by removing the surface moisture by means of blotting-paper before hanging up to dry. 3. Printing. The ink is deposited on parts which should remain clear.—This is caused by the plate becoming too dry, horn not having been damped enough before rolling up, or, in hot weather, from the rapid evaporation of the moisture, which may be obviated by the use of the damping mixture b fore m ntioned ; but if, by accident, it should occur, as soon as it is observed, the parts should be gently rubbed with a flannel, which will generally remove the ink, or the plate may be damped ami the ink removed by rolling in quickly and dragging the roller smartly over the parts. There is a much more serious defect, which, if neglected, may result in the loss of the plate. It is termed “ smutting up.” The detail becomes obscured in a black patch, which resists all inodes of cleaning. The causes of it are very numerous. Among the principal are:—Etching solution is too weak. Excess of moisture on the paper or stone. Ex treme heat or cold. Use of soft bad ink. Dirty sponge. Contact of a greasy body. Friction with the finger. It must be remo lied, ai soon as it is discovered, by washing the ink oft with turpentine, and rolling in again with hard ink, damping with the gum solution. The lines are doubled or spread. This arises from several causes, among them:—Slackness of the tympan causing it to be too close to the plate, which prevents the free extension of the paper. Use of paper too dry or badly damped, and of which the edges have become drier than the centre. The remedy is to fix the paper in the tympan, which should be raised slightly off the plate, so that the simper may act gradually on the piper. Most of the failures in this process arc the result of simple mechanical defects, the causes of which are uot difficult to discover, aud which may be easily remed i ed. Photo- ZINCOGRArIY in Half Tones. Photo zincographs of ordinary photographic views, &c., can be obtained, but the results are not satisfactory unless they are considerably retouched. The process is much more suited for the reproduction of architectural details. Seme ex cellent specimens of this process, consisting of views of Netley Abbey, Jerusalem, and Stonehenge, have been published at the Ordnance Survey Office, and I will describe the process by which they are produced. The sensitive transfer paper is prepared in exactly the same manner as for subjects in line, but is kept for about a week before it is used ; the effect of this is to slightly decompose the surface and make it more capable of retaining the ink. The negatives should be good, and may be denser than is usual for silver printing, as the paper is more sensitive, and there is no after-reduction of the intensity. The exposure varies from five minutes to a quarter of an hour, more or less, according to the intensity of the light and the quality of the negative. The inking is con ducted in the same manner as for line work, but the ink may be harder and the pressure greater. The development is the most important part of the process, and requires great skill and experience to ensure success. The prints, coated with ink, are laid face downward on lukewarm water, and allowed to remain till the gelatine is softened ; the surface ink is then gently removed by washing the surface with a very soft sponge and warm water, taking care not to scrub it at all. The print is then immersed in warm water, which is gently agitated, and the detail will gradually appear ; the water is changed after a short time, and the operation repeated, the prints being allowed to soak for an hour or so between each change. When most of the unaltered gelatine has been removed and the print appears to have soaked enough, it may bo finished off by again washing with sponge and warm water ; it is then hung up to dry. When dry, the print will appear darker than a silver print of the same subject, but that will be remedied when it is transferred to zinc. The transfer to zinc is the same as before described. The printing must be conducted with as great care as is re quired for the finest chalk drawings, and the damping solution must be used. Photo-zincotypy. I have made a few experiments with a view to obtaining a raised printing surface on zinc by means of photography, and, from the results I obtained, am of opinion that the process might be practised with success for the reproduction of diagrams, woodcuts, &c., to bo printed with type. I have not worked it out thoroughly yet, but will describe the pro cess, in order that others may be induced to experiment in this direction. A photographic transfer is made on to a fine grained zinc plate in the manner described before. Care must be taken to have the lines very perfect, or good results cannot be obtained. The ink is washed off with turpentine. The plate is rolled in with an ink composed of:— Bitumen ... ... ... ... 4 parts Litho printing ink ... ... ••• 2 , Wax ... 1 „ Burgundy pitch ... ... ••• 1 » Turpentine middle varnish... ... 1 „ When this is done, the plate is left for twenty-four hours till the varnish is quite dry. The back is then covered with wax or Brunswick black, &c., and the plate is connected with a copper plate at about a distance of a quarter of an inch. The two are then plunged into a 70-grain solution of sulphate of copper, and after a short time the subject will