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
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
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• Strukturtyp: Ausgabe

JANUARY 16, 1885.j THE PHOTOGRAPHIC NEWS. 35 which we reproduce as Meisenbach blocks ; it is needless to say that the exposure was equal in each case. The general sensitiveness of the two plates used was as nearly as possible the same ; but the much greater range of the eosine plate (Clayton and Tailfer) is obvious at a glance. In order to make the comparison between the two plates complete, a reproduction of an ordinary sensitometer trial is also given FRENCH CORRESPONDENCE. Progress in 1885—Red Rays only Non-actinic—Con trolling Rapidity of Sensitive Plates—Antwerp International Exhibition. Forthcoming Progress.—As I am incapable of adding any thing to the complete retrospective review published at the commencement of the last number of the Photographic News, I am limited to assert its accuracy, and express hopes as to the progress to come during the year. With out being a great prophet, I can foretell that now, since so many improvements have been made in instantaneous photography, much may be expected in that direction, particularly in two ways: firstly, by finding more active developers capable of bringing out the slightest traces of the action of light; and secondly, by the preparation of emulsions still more sensitive than those in present use With regard to the perfection now reached in photo engraving, one can reckon on having more and more tx- tensive application of it in its varied forms. When better known, and its advantages fully recognised, it will be used more largely in the illustration of books and periodi cals ; and, I am sure, will reach to the more artistic level of ceramic decoration, to which it has been scarcely at all applied. Non-actinic Rays.—The question of dark room lighting has been the subject of many experiments of late, and I myself wished to take count of the facts observed by Mr. Debenham. At the outset I must say that I have not been able to succeed according to his indications. All kinds of green and yellow light, and mixtures of the two colours, gave me a distinct luminous impression on any sensitive plates. It is true that the action on ordinary bromide of silver emulsion is weak if the source of light be tolerably distant, as shown well in my colour sensitometer ; but if isochromaticemulsions be used, the rays must be distinctly red. If a perfectly monochromatic yellow light were at one’s disposal, one would have nothing to fear for gelatine plates; but the ordinary flames, in spite of green or yellow glass, are polychromatic, and contain blue and violet, as may be seen with the help of the spectroscope. Standard Jor Determining Rapidity of Plates.—The idea of a definite understanding relative to an adopted controlling method for the rapidity of various sensitive firns is spread ing through several photographic societies. I cannot fore tell which solutions will be accepted, but, for my own part, I suggest the followingThe scale should be con structed similar to Mr. Warnerke's—that is to say, formed of a succession of films more and more opaque superposed on a plate of glass. To execute the scale, simply consists in the formation of a negative, to serve for counter prints on gelatine plates of a known degree by the help of a con stant source of light lasting a certain length of time, deve loping with ferrous oxalate, the proportion of oxalate of potash to sulphate of iron being always the same. By this simple method a certain number of scales will be made, and afterwards compare 1 one with another to throw out those not identical with the standard scale. The scale con- sbucted—what is its cost? Monckhoven quarter-plate cost four francs (3s. 2d.) the dozen, and by doubling the cost of a single one for the expense of developer, it comes to about sevenpence without mounting the print or mauu- Tacturing expenses, which might bring it up to eighteen- pence or two shillings. For the source of light I advise a good stearine candle, the base of the flame corresponding to the height of the centre of the scale, placed at the dis tance of 50 centimetres. The exposure ought to be half a minute exactly, after letting the candle burn five minutes. Under such easy conditions a practical method will be obtained for controlling the varied rapidities, and com paring them with one another, at a very trifling cost. Anticerp Jnternational Exhibition.—About forty French photographers have given in their names to exhibit in the photographic section of the forthcoming International Exhibition at Antwerp. 1 think Messrs. Boussod, Valadon, and Co.’s photo-gravures will excite a great deal of atten tion and admiration. LEON VIAL. IVES’ ISOCHROMATIC PROCESS WITH CHLOROPHYL. BY DR. H. W. VOGEL. In the Year-Book for 1885, page 111, I find an interesting article of Mr. Ives, Philadelphia, on his isochromatic pro cess with chlorophyl. In this article Mr. Ives mentions also my researches in this matter, and says :—" Dr. Vogel was undoubtedly the first to suggest the use of dyes for increasing the colour sensitiveness of silver bromide ; but he was not the first by several years to publish a practical, useful process,” &c., &c. I beg to remark, as to this assertion of Mr. Ives, that, eleven years ago, I did not confine myself to make only suggestions or spectrum photographs, but that I showed by experiment, already described in my first paper, published in the Photo- graphische Miltheilungen, 1873, and in the Photographic News, 1874, that my new process of making bromide of silver sensitive to the so-called non-actinic rays was of real practical value. I reproduce here the lines in question from my paper of 1873 :—“ I took a picture of a blue ribbon on yellow ground. With an ordinary bromo iodized plate I got a white ribbon on a dark ground. On a bromide of silver plate, stained with coralline, I could not hope to get anything, because blue and yellow rays acted on this plate with the same energy. Therefore I put in front of the lens a yellow glass, which let pass the yellow rays, but absorbed the blue ones, and now I obtained with suflicient exposure a dark ribbon on a light ground." I think this picture, taken in 1873, in the described manner, was the first isochromatic photograph taken. It may be possible that chlorophyl (first proposed by Becquerel, 1875, for increasing the sensitiveness of the bromide of silver for red rays) may give better results than coralline. But, surely, the chlorophylZprocess is not the first isochromatic process published? Even the modus operandi of Mr. Ives is not new. Mr. Ives soaks bromide of silver plates in chlorophyl solution. Exactly the same method of preparation I em ployed in 1876 {Photographische Mittheilungen, xii, page 286), and I recommended it for all dyes which are affected by free acid in collodion. But if anybody would ask why my first isochromatic process was not acknowledged sooner, I answer that I had exactly the same experiences in 1874 as Mr. Ives in 1879. Nobody would believe me. My late friend Monckhoven, Carey Lea, Lockyer—in short, all leading men in photography and spectrum analysis—doubted my assertion ; they repeated my experiments in a wrong way, and without success, and 1 have had to do very much to defend my position. In the meantime the photographic processes have made important progress, so that now many processes are easily worked out by any amateur which could be performed ten years ago only by experi enced investigators. On the other hand, new and more powerful optical sensitizers are discovered, and in this way the improved isochromatic processes have now more practical success than that first published e'even years ago.