The photographic news

• Bandzählung: 13.1869
• Erscheinungsdatum: 1869
• 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-id1780948042-186900000
• PURL: http://digital.slub-dresden.de/id1780948042-18690000
• OAI: oai:de:slub-dresden:db:id-1780948042-18690000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Heft 545 (S. 73-84), Heft 547 (S. 97-108), Heft 589 (S. 599-610) fehlen in der Vorlage. Paginierfehler: Auf Seite 444 folgt Seite 443
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

THE PHOTOGRAPHIC NEWS. 258 by means of the sulphate of iron developer, and when the particles of silver have attached themselves to those por tions of the plate reduced by the action of the light. The picture, therefore, is made to appear by reason of a power which attracts the suspended molecules of metal to the surfaces acted upon by light. The greater the surface of the negative acted upon by light, the more the precipi tated molecules are distributed over the plate; and, on the other hand, where but few lights exist (in the positive), the concentration of the silver particles at these points will be greater. For this reason it is that hands which rest upon an absolutely dark ground appear intensified out of all proportion, and thus lose all appearance of model ling. The silver molecules are likewise strongly deposited at those portions where iodide or subiodide of silver first attracts them; and in this manner the luminous band is caused which is so often observed at the margin of repro ductions of black velvet drapery. In this explanation great stress is rightly laid upon the influence of the superfluous nitrate of silver upon the plate. From the valuable researches of Dr. W. Reissig we have already learnt that, in the wet process, a chemical reaction really takes place, that the iodide of silver is converted by the action of light into subiodide, and the free iodine given off transforms a further quantity of the nitrate of silver into iodide and iodate of silver; and, further, that the presence of nitric acid liberated by this metamorphosis can be demonstrated by the fact that an acid reaction is obtain able at those portions of the negative acted upon by light. The concentration of the nitrate of silver upon the plate, after exposure, is very unequal, and its reaction more or less acid. While, therefore, on those parts of the negative which are not affected by light, an undiminished quantity of nitrate of silver is present, the latter is in part consumed, through chemical agency, by those portions of the surface the most acted upon, and in this fact we may see something to help us with the solution of the question of solarization, and the reason of its occurrence. We have enjoyed fre quent opportunities of remarking, during the reproduction of engravings, that a portion of white ground, where there was a large surface of it, sometimes became perfectly solar ized, and, notwithstanding all further manipulation, was in capable of assuming greater vigour ; while another portion, of white ground lying between dark lines, allowed of a thicker covering, which gradually increased the nearer the strokes were together, and the more free nitrate of silver there was on those parts. All these results are in harmony with the conclusion that such precipitates which are formed in opposition to the action of light upon the negative, and which produce upon the positive a luminous line encircling the dark objects, are the result of unequal development. This decision we should have had some hesitation in pronouncing, had not the results of certain experiments, undertaken in con junction with the well-known photographer, M. Josef Hoffmann, proved to us the fact very conclusively that the luminous band is always formed in the direction taken by the developer in flowing off the plate, or, rather in that direction where the solution passes from an indifferent portion of the negative to a strongly-lighted part. A velvet dress was photographed several times successively, and the developer poured on from the left, and allowed to flow off at the right. The precipitate (the luminous band in the positive) was perceptible on the right edge of the velvet drapery, while on the left not the slightest trace of the line was visible. On repeating the experiment, and pouring the developer in a diagonal manner over the plate, the line was found to become apparent in the same way, and from the opposite side to that on which the developer was applied. We have obtained a series of pictures show ing the light band sometimes on the right side, and some times on the left, all of which were produced without in [May 28, 1869. any way altering the position of the camera, the method of lighting, or the disposal of the velvet drapery. Ilie shorter the exposure the less detail was there perceptible in the velvet, but the more defined was the band of light, which became apparent as soon as the picture was perfectly developed. Many operators incline the plate backwards and for wards during development, so that the solution flows con tinually over the negative. In such cases the precipitate will be perceptible all round the dark image, as the mole cules contained in the superfluous liquid on the plate, having been endowed with a tendency to become precipi tated by the addition of the reducing agent, pass over sur faces indifferent to them to those portions where they are attracted, and where, consequently, a rapid precipitation occurs ; and the greater the deposit of metallic molecules the stronger is the attraction exerted upon other particles of silver still in suspension. In a negative of this kind it is possible to perceive a distincly perceptible relief on examination’with the naked eye. It will, we fear, be a somewhat difficult problem to dis cover a method of preventing this false luminous effect. PHOTOGRAPHIC EXPERIMENTS. BY H. J. NEWTON.* Acetate OF Morphia—Coffee—The Tea Process— e Gum Process—River Water—Developers. About a year since, the use of the acetate of morphia was introduced as a preservative, but it proved to be only a sensi tizer, without any of the qualities requisite for a preservative. Plates prepared with it were very nearly as sensitive as wet ones, but they kept no longer, if they did as long, had nothing been done to them but simply washed. I tried it also on paper for paper negatives with the same results. The idea suggested itself to me, that by combining the acetate of morphia with tannin, I might retain the sensitive qualities of the morphia and the keeping qualities of the tannin. I made a few plates and kept them several weeks; they showed no signs of change, and were as sensitive as those prepared with morphia only, and I exhibited some negatives made on chose plates to this Society, which were exposed thirty seconds, according to my recollection. I found, however, in a short time, that there was a lack of harmony in the solution; it had undergone a change which rendered it unfit for use as a preservative. I then made a compound of opium, sugar of milk, and tannin, calculating to get the morphia in the opium in a form that would not be as susceptible to change. After a few trials I found that the following proportions answered my purpose, not only making a very clear and brilliant solution, but one that will keep indefinitely. I have some now on hand which has been made nearly eight months, and there has been no per ceptible change. I use — Hot water ... 6 ounces Finely pulverized sugar of milk 4 ounce Tannin ... ... 40 grains Tincture of opium } drachm Put together in the order here given. The sugar of milk dis solves very slowly unless pulverized, and hot water be used. The addition of the opium causes a precipitate in the solu tion, and it should stand at least twenty or thirty minutes before it is filtered. I prefer sugar of milk to any other saccharine substance, for the reason that, unlike all others, it is not liable to alcoholic fermentation, which always pre cedes putresence, or the generation'of putric acid in sac charine solutions. With plates prepared with this pre servative 1 have made negatives in the month of June, with 4--inch focus lenses, -inch diaphragm, in five and six seconds, with the alkaline developer, which was quite as quick as I could make them with wet plates. * Continued from p. 225.