The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• 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-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

THE PHOTOGRAPHIC NEWS. LAvaUsT 21, 1885. lias at present shown, the prints most affected are those made with an emulsion containing a minimum of an organic salt, the red colour of this latter silver compound appearing to offer a greater resistance than the violet silver chloride to the reducing influences on the vigour of the image. In practice it may sometimes happen that from in attention or other preventable causes, positives either on opal or paper become too much impressed by the action of light, and the ordinary routine of toning and fixing does not bring them back sufficiently; they still remain very much too dark. This may be remedied in either of the above instances by putting them into a reducing agent composed of:— Potassium cyanide ... ... 1 gramme Liq. ammon. fort 1 cubic centimetre Water... 1 litre The proofs should be agitated in the above solution until the desired reduction has taken place. When it is intended to reduce positives by this means, it will be better not to tone quite so much, since the reducer has a tendency to grey the image somewhat. It is not a matter of so much consequence in the case of prints that are to be mounted on waxed or talced glass plates for stripping, since these do not dry very much colder in tone then they appear in the washing bath ; but prints dried in the ordin ary manner lose very much redness in that operation. Unfortunately (in some respects, perhaps) hot burnishing is not favourable to any class of gelatine prints ; they all succumb more or less to the successive heatof the burnish ing tool; they fare very much better, however, with the old-fashioned rolling-press, and it is an open question whether prints passed through an ordinary rolling-press are not as pleasing as those which have been highly glazed. This question it is not our business to answer, but we re commend those who desire highly glazed surfaces to adopt the plan at present used for enamelling; there is an ex ception to our remarks, inasmuch as paper prepared with a minimum quantity of gelatine stands a better chance of receiving a burnish; the print must, however, be in a dry condition, the burnisher only moderately hot, and the print well lubricated. The best lubricant we have tried is finely pulverized curd soap applied by means of soft rag. Liquid lubricants, whether of an alcoholic or other rapidly evaporating nature, would not answer so well. A purpose, which we have not hitherto mentioned, to which some of these emulsions on opal (such as we have de scribed) can be advantageously utilized, is worthy of more than passing note; we refer to its suitability as a surface from which to make enlargements. When larger sizes are required from a small but satisfactory negative, it is usual to make the transparency and enlarged negative by trans mitted light. Objections to this method have been fre quently pointed out, but the remedy was not forthcoming. In this process we gain considerable assistance by making a good positive by contact printing on an opal plate coated with gelatino-chloride of silver, and making the enlarge ment direct in the camera, using reflected light. The. (/rainless surface, and the possibility of getting any depth of shade with the printing frame before named, or actinic quality of colour to suit the strength of negative, are considerations likely to aid materially in the produc tion of good enlargements. The positives obtained by this process may be worked up to any reasonable extent, when the necessities of the case require it, the surface lending itself to that purpose in every way equal to the carbon opal, or the original pro duction with collodio-chloride of silver. When the degree of enlargement doesnot exceedfour diameters,any working up of the positive in monochrome need not appear in the least obtrusive in the enlargement. Altogether, the method offers considerable improvement upon either the transparency modes, or that of copyingfrom paper surfaces. Transparent positives made by the formula we have given are capable of producing very good enlargements provided they are printed sufficiently deep to get all the detail obtainable. This stage is not reached until the image is fully printed through the entire film, and all the tones in the negative can be readily seen on the back of the plate (of course clear glass plates are used for this purpose.) Notwithstanding the extreme beauty of such transparencies, we think them more useful for decorative purposes or the lantern, than for reproducing negatives. Yet we have produced very good enlarged negatives from transparencies of this kind, without showing any more texture than the original contained. We would now draw attention to other ways in which compounds with silver chloride in conjunc tion with gelatine can be applied to direct positive printing. The previous articles have dealt with emulsions contain ing insoluble silver haloids suspended in the gelatine, but now wo propose treating of paper more nearly allied to albumen in the method of its preparation and general characteristics; at the same time it is wholly free from that substance. Tbe subject we are now dealing with is one worthy the serious consideration of experimentalists, since it opens the road to a new departure, which we apprehend will exercise a greater influence on the future of silver printing by means of albumenized paper than anything we have hitherto mentioned. In looking about and experimenting for the purpose of finding something to take the part of organifier that albumen plays in the paper beating that name, we tried many substances. The majority of them, though very active, laboured under the disadvantage of being soluble in cold water, and not coagulating in the presence of silver. Out of the very few to which we were ultimately confined, that which seemed to add the largest amount of energy to the printing property of the silver salts was starch ; the form in which we prefer to use it is that known as arrowroot, and the better the quality, the more perfect the jelly-like product obtained on boiling. The ordinary starch powder procured from the druggist will answer well, but there is a slight grain on account of the minute size of the starch granules composing it. The microscope quickly reveals the character of a proposed fecula, and the clearness and tenacity of the jelly confirms the revelation of the lens. Potato starch, if well washed and freed from impurities, is good for our purpose also ; but in this there is a mixture of granules, the majority being large, while the rest are small, sometimes very small indeed. The manner in which we use the starch is to mix it with a hard gelatine, and then to salt the whole ; coat paper, and float that paper, when dry, upon a bath of silver nitrate. The details of these processes we now propose to give, prefacing our remarks with the suggestion that there is a wide margin in which to work, it being possible to modify the propor tions, and vary the salts employed to some considerable extent. If paper be thickly coated with plain gelatine and then floated on a silver bath, after prolonged exposure in a good light, an impression will be produced—faint, and of a pink tinge; but if starch be substituted for gelatine, a picture of much greater vigour will result. When silver chloride or citrate is added to a solution of starch, the latter in creases the vigour of the former considerably, but plain starch produces insufficient surface, and is too liable to injury, so we find the purpose is answered if a little starch jelly is mixed with dissolved gelatine, and the compound salted, ready for floating on silver when dry. A certain amount of body can be given to such a mixture by the addition of barium-sulphate, but it must be the finest possible precipitate that can be obtained. The ordinary method of taking barium-chloride and gelatine in solution, and sodium-sulphate, also dissolved with gelatine, and mixing the two solutions together in order to obtain barium-sulphate, dees not produce a precipitate of sufficient delicacy. Only by having exceedingly dilute solations in water of the two salts, and well washing the