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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1308, September 28, 1883
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The photographic news
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Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band 27.1883
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THE PHOTOGRAPHIC NEWS. VoL. XXVII. No. 1308.—September 28, 1883. CONTENTS. PAGE The Intensification of Gelatine Plates 609 On Backgrounds 610 Coloured Photographs on Glass 611 The British Association 612 Photographic Copyright 613 Photo-Lithography and Photo-zincography. By Major J. Waterhouse, B.S.C 615 Notes 616 Patent Intelligence 618 PAGE Lessons in Optics for Photographers. By Capt. Abney... 618 Solid and Liquid Illuminating Agents. By L. Field, F.C.S. 619 A Dictionary of Photography 620 Correspondence 621 Proceedings of Societies 22 Talk in the Studio 623 To Correspondents 6;3 The Photographic News Registry 624 The Every-Day Formulary 62 THE INTENSIFICATION OF GELATINE PLATES. Among the many subjects brought forward at the Technical Meeting of the Photographic Society last Tuesday, was the subject of intensifiers. The discussion resolved itself into one on “ Which is the best intensifier ? ” and it was most noticeable what different opinions were expressed by different members, amounting in many instances to direct contradictions. It has often been regarded as a drawback to the gelatine process, that a perfectly satisfactory intensifier cannot be found for it. There have been and are intensifiers innu merable, but a vast difference of opinion exists as to their respective merits, whilst the majority of good workers are apt to regard all alike with disfavour, and prefer to throw away a defective negative, unless its subject is of special interest to themselves, or possesses pecuniary value, rather than submit it to the somewhat uncertain and usually disagreeable process of intensification. Nor is this to be Wondered at, for—and here arises a point often lost sight of by photographers—intensification occupies altogether a different position in regard to gelatine than it does to collodion. With the old wet plate process, intensification (or redevelopment, as it was often called) was part and parcel of the production of a good picture. The first thing to be attained was a good clear negative with sufficient detail and then this was built upon till it attained suffi cient printing density. With regard to gelatine, the case is very different. Not only is it possible to obtain suffi cient density by the reduction of the haloid salt within the film, but the best result is obtained when the negative requires no subsequent treatment. In fact, the necessity for intensification is in itself a defect, and can in most cases be put down to one of the following causes :— A thinly coated plate. Insufficient development. Under- or over-exposure. In the early days of gelatine, recourse was had to silver intensifiers, but it was soon found that there was extreme danger of spoiling the negative by staining it. Then the many intensifiers containing the salts of mercury were re suscitated, and found to give fairly satisfactory results with gelatine. There are many drawbacks to the use, however, of nearly every one of them, nearly all of them giving us scarcely sufficient control over the density, and some of them being affected by the air and other causes. How many negatives intensified by mercury have been rendered almost useless by the change produced in them after having been kept for some time ! Although we now possess a knowledge of a few formula; which answer their purpose sufficiently well, it cannot be that photographers are perfectly satisfied with the existing state of things. Felative to the question of getting an intensifier the re ¬ sults of which should be permanent, we recently tried to apply the old lead intensifier to gelatine plates. Our ex periments met with but indifferent success, and of them selves would scarcely be worth recording, but they demon strated so well the difficulties involved in intensification generally, that we think it desirable to record them. The intensifier in question, which was brought before the photographic world by Eder and Toth before the discovery of the gelatine process, consists of 20 grains of nitrate of lead and 30 grains of red prussiate of potash dissolved in 1 ounce of water. After a plate had been treated with this, it was washed, and flooded with dilute ammonium sulphide, a permanent brown deposit of sulphide of lead being the result. W e used the first solution only half the strength of the above. We first took plates whose thinness was due to the coat ing of the emulsion itself, and others whose lack of density was due to insufficient development. In all cases the whites were perfectly clean. After thorough washing in tap water and a good rinse in distilled, to remove all sulphates, they were treated with the lead ferricyanide solution till they were of a whitey-brown colour throughout. They were then well washed in distilled water, and treated with the sulphide. A remarkably dense image was the result. Even the thinnest images, provided the whites were perfectly pure, could be brought up to printing density. If, however, the plates were insufficiently washed, or washed with water containing a slight trace only of sulphates, a yellow veil was produced which, though not absolutely interfering with the printing, was of a remarkably non- actinic nature. So much care had to be taken in the wash ing that it wasplainly evident that the use of this intensifier was quite out of the question for ordinary purposes, though it might answer in special cases. With plates that have been under- or over-exposed, in tensification is always more or less unsatisfactory. An over-exposed plate is necessarily veiled, and an under exposed one is usually veiled on account of its being left in the developer till the photographer is sure that he can get nothing more to appear. Not only is the image rendered denser, but the veiled portion is also intensified, though to a somewhat less degree; the picture requires a long time to print, and it sometimes loses a little in sharpness. Our experiments with the lead intensifier gave the same results, but to an exaggerated extent. In the course of our experiments, we met with one result that astonished us in no small degree, and which is of considerable interest on account of the light it may throw on the phenomenon of reversal, borne time since, we bad produced some reversed negatives direct from the original negative by over-exposure. Chancing to take up one of these that was capable of giving a fair print, yet would, nevertheless, be the better for a little in tensifica-
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