The photographic news

• Bandzählung: 12.1868
• Erscheinungsdatum: 1868
• 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-id1780948042-186800009
• PURL: http://digital.slub-dresden.de/id1780948042-18680000
• OAI: oai:de:slub-dresden:db:id-1780948042-18680000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

THE PHOTOGRAPHIC NEWS. Von. XII. No. 508.—May 29, 1868. CONTENTS. PAGE Mr. McLachlan’s Discovery 253 The Retouching of M. Adam-Salomon’s Pictures 254 Mr. McLachlan’s Nitrate of Silver. By John Spiller, F.C.S. ... 254 Pictorial Effect in Photography. By II. P. Robinson 255 Gradated Backgrounds for Heads, etc. By R. Gillo 256 Photographic Printing in Silver, Theoretical and Practical. By W. T. Bovey 256 Collodion-Cuir and the Carbon Process. By M. Despaquis 257 PAGE On the Preservation of Collodionized Plates in a Moist Con dition. By General Mongin 258 Remarks upon the Wet Collodion Process. By Mr. McLachlan 259 Proceedings of Societies—Liverpool Amateur Photographic Association 261 Correspondence—Sei Clement—Injury to Negatives by Var nishing 262 Talk in the Studio 262 To Correspondents 264 MR. McLACHLAN’S DISCOVERY. We shall now endeavour briefly to state what appears to us to he the suggestions to be derived from Mr. McLachlan's experiments. The chief feature of his operations appears to consist in his care to produce a neutral bath. In stating this, it is only fair to say, however, that he himself very emphatically denies that the issue of his treatment of the nitrate of silver solution simply results in the production of a neutral bath. He insists that some unknown, unrecognized change is effected by the action of light on the neutral silver solution, by which it acquires new properties quite distinct from those of any bath, either acid, alkaline, or neutral, hitherto known. We must decline, however, to refer to occult causes results which can bo assigned to known agencies ; and pending the further test of experiment, which it is always fair to Mr. McLachlan to hold in reserve, wo may without impropriety consider how far the good results he has described may bo consistent with much that is already known, but the importance of which is possibly not suffi ciently recognized. Mr. Spiller’s experiments lead him to believe that the re sults described by Mr. McLachlan arc due to the presence of a trace of chloride of silver present as an impurity in the nitrate used, and this view is strengthened by an examina tion of the sample of Mr. McLachlan’s favourite nitrate, details of which will be found on another page. Whether this be the explanation or not, Mr. Spiller’s experiments have shown that a 20-ounce bath to which 1 grain of chloride of sodium had been added, after sunning for some weeks, and treating with caustic potash, as directed by Mr. McLachlan, gave, with a collodion rendered colourless and neutral by treatment with a potash solution, perfectly brilliant and clean pictures, without any trace of fog, as an example now before us proves. Thirty drops of a solution containing half a grain of caustic potash in an ounce of water were added to the pint of nitrate solution, which was, according to Mr. Spiller, rendered quite neutral, and according to Mr. McLachlan decidedly alkaline. We may here, by the way, remind Mr. McLachlan of a fact which seems to have escaped his attention, and may have misled him in some of his con clusions. He assumes that the bath is necessarily in an alkaline condition, because it slowly restores the blue colour to reddened litmus paper. He should remember that a solu tion of perfectly pure nitrate of silver will restore the blue tint of reddened litmus paper. We return, however, to the fact that a bath so free from any trace of free acid as to slowly restore reddened paper, and a collodion rendered colourless by caustic potash, did give clean brilliant negatives. This is, of course, not absolutely novel, but it is certainly rare. The tendency of working in late years has been to a decided increase in the use of nitric acid in the negative bath. The neutral bath and freshly mixed simply iodized collodion in a colourless neutral state, which many years ago were regarded as securing the perfection, of conditions, are now almost unknown. When simply iodized collodions were employed, the least trace of nitric acid in the bath was fatal to sensitiveness, and it was never employed; but, since the use of bro mo-iodized collodion for negatives has become universal, nitric acid—which, when bromides are present, interferes little with sensitiveness—has been largely used as a means of preventing fog in a bath which would otherwise give dirty negatives. The free use of nitric acid has, in fact, often permitted the use of a bath con taining considerable impurity. Now, we are by no means sure that the use of nitric acid intolerably large proportion is an evil. Wo have used it freely for many years without suffering any serious inconvenience which we can trace to its use. But there are certain evils which may result from its use which are worth considering. In the first place, if a collodion containing a very small proportion of bromide be employed, nitric acid will impair sensitiveness. In the next place, under many circumstances it tends to the formation of a thin grey metallic-looking image, instead of the dense brown image desirable in a nega tive. In the next place, its presence in the nitrate solution will tend to oxidize the alcoholic bodies accumulating in the bath, and to cause the formation of aldehyde, and so gradually induce the fog it was added to prevent. And finally, the presence of nitric acid increases the tendency of the bath todissolve iodide of silver, which will, therefore, more rapidly increase in the bath the greater the proportion of nitric acid present, and so promote the accumulation of one source of pinholes. Having regard to these considerations it may be well worth while to consider whether the system, the practicability of which Mr. McLachlan’s experiments suggest, of working with a perfectly neutral bath, and a collodion without any trace of free iodine, by which nitric acid would be liberated in the bath, may not possibly tend to diminish or eliminate many of the evils which are occasionally troublesome in the ordinary mode of working. Confirmatory experience is not found wanting. Many photographers have stated that a nitrate bath neutralized and sunned often works admirably without any addition of acid. Mr. Blanchard has more than once stated this fact in our pages. Mr. England, who works with a nearly neutral silver bath, also works with' a perfectly colourless collodion ; and the practice of some other authori ties tend in the same direction. The fact that the iron developer yields cleaner and brighter results when it contains a trace of a persalt is not new, but has long been held by the majority of the practical photographers. Mr. McLachlan's somewhat roundabout mode of securing the oxidation of the iron salt does not, so far as we can at present see, possess any advantage over the simpler known methods.