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The photographic news
- Bandzählung
- 7.1863
- Erscheinungsdatum
- 1863
- Sprache
- Englisch
- Signatur
- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
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- SLUB Dresden
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- Public Domain Mark 1.0
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- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Parlamentsperiode
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- Bandzählung
- No. 234, February 27, 1863
- Digitalisat
- SLUB Dresden
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Zeitschrift
The photographic news
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Band 7.1863
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- Register Index 619
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Band
Band 7.1863
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- Titel
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THE PHOTOGRAPHIC NEWS. Vol, VII. No. 234.—February 27, 1863. CONTENTS. PAGE Photographic Soirees 97 On a Process for Direct Intensifying 97 Photographic Exhibition.—Fifth Notice 98 Critical Notices 99 Collodion Wet and Dry. By M. L’Abbe Despratz 100 Glasgow Photographic Association. — Soir&e, Exhibition, and Conversazione 101 The Application of Photography to the Magic Lantern Educa tionally Considered. By Samuel Highley, F.G.S., F.C.S. ... 104 PAGE New Process for Positive Printing. By M. Bertrand. 101 Proceedings of Societies 105 The International Exhibition.—Report of the Jury 105 Photographic Notes and Queries 106 Miscellaneous 107 Talk in the Studio 108 To Correspondents 108 Photographs Registered during the Week 108 PHOTOGRAPHIC SOIREES. A VERY successful soiree of the Loudon Photographic Society was held on Friday evening last, at the Gallery of British Artists, in Suffolk Street, where the exhibition of photographs is now held. A brilliant company, including many persons of distinction, thronged the rooms, examining the excellent display of pictures until a late hour. We call the especial attention of our readers to a copious report, on another page, of a very brilliant soiree, held by the Glasgow Photographic Association. Indefatigable efforts had been made to secure a first-rate collection of photographs for exhibition; very able and interesting speeches were delivered, various photographic illustrations and experiments made, amongst which the crowning one was the production, by the aid of the electric light, of a portrait negative; Mr. Jabez Hughes, whose name is well known to our readers, being the sitter. From this a transparency was immediately produced, and, in the course of a few minutes, the portrait was perfected on to the screen of the magic lantern, and shown, amid much enthusiasm, to the entire audience. We commend the account of this soiree to photographers, because it exhibits an amount of energy, unity, and enthusiasm among photo graphers, rarely witnessed, but worthy of all emulation. ON A PROCESS FOR DIRECT INTENSIFYING. M. BLANQUART EvRARD has addressed the following com munication to the Paris Photographic Society and recorded in the Bulletin. It has. for a long time been known that when a sensitized surface is exposed to light, after it has been impregnated with a reducing salt in solution, we obtain, upon removal from the camera, a completely developed image. In ordinary practice, in which the sensitized film only is exposed in the camera, the image obtained by the exposure remains latent until revealed by a reducing solution. Three agents, therefore, concur to produce the image. 1. A sensitized film (sensitized collodion.) 2. Light. 3. A developing salt. (Sulphate of iron, gallic and pyrogallic acid.) I shall not occupy myself in this place either with the sensitive film or with the reducing salts whose action varies ; the sulphate of iron precipitates the silver in the metallic state; the gallic and pyrogallic acids form with silver, in my opinion, gallates of silver more or less coloured ;—but I shall examine the action of light, from which it seems to me possible to derive a new resource under certain circum stances. It is admitted that there is a complete formation of the image by the exposure to light, however short may have been its duration. We may then infer that if the image does not entirely appear under the action of the reducing salt, it is because the latter is not sufficiently subtle. It remains, then, to find a reducing salt capable of revealing the image in all its strength. But has the sensitive film itself been so deeply impressed as to be able to transmit afterwards the image in its entireness ? From what occurs in ordinary practice, we may be allowed to doubt if it does. When the exposure has been too short, the image is formed only on the surface of the film. It results from this, that the layer of reduced silver has not sufficient thickness to oppose a sufficient obstacle to the passage of light. In taking the positive, we obtain only a pale and ineffective design. If, on the contrary, the exposure has been too long, the reverse action is produced, the parts most lighted assume too great an importance. The details in the lights disappear, in com pensation we obtain details in the shadows which a short exposure would not have given, but the picture is none the less poor and inharmonious. The negative is lost. The point at which we must stop the exposure is then very difficult to seize upon. There is an equilibrium to be pre served, which becomes impossible under certain conditions of lighting and colour. We employ, it is true, different means to give either more importance to certain parts of a negative, or to diminish the value of certain others, but these partial intensifyings, by means which I am almost tempted to call mechanical, are almost always defective. Thus far, then, we have actually acquired the possibility of intensifying a negative as a whole, and still the means em ployed are hazardous, and very often compromise its exis tence by causing a softening of the collodion, wrinkles, rents, &c. Besides, it seldom happens that a successful intensify ing does not cause the image to lose a portion of its primitive delicacy. For the chemical means hitherto employed we must sub stitute a more inoffensive method, so as to develop any portion of the image at pleasure, by localizing the operation, either by too short an exposure, or that the colouring of certain objects adverse to the photogenic action be suitably modified. This method will be the continuation, under certain con ditions, of the action of light upon the sensitive film, or, in other terms, the light completes the manifestation if the image formed in the camera. I sum up the principles upon which my theory is based. On removal from the camera, the image in its entireness is imprinted on the sensitive film. The impression is more or less decided, according to the duration of the exposure or the intensity of the light. The image is visible only after being developed by the reducing agent, and it is not till then that we can judge its value. However, if before developing the image we assume that the exposure has been insufficient, and that we desire to augment it, we have only to remove the cap from before the
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