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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 216, October 24, 1862
- Digitalisat
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Zeitschrift
The photographic news
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Band 6.1862
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- Register Index 619
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Band 6.1862
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October 24, 1862.] THE PHOTOGRAPHIC NEWS. 509 * From the Intellectual Observer. failures in printing, since I have only taken the proof in a state of perfect readiness for the toning process, and the suggestion that foreign salts are formed on the surface that interfere with toning, only strengthens this theory, since electricity will only form deposits on clean surfaces. PHOTOGRAPHIC DELINEATION OF MICROSCOPIC OBJECTS. nr GEOnGE s. BRADY, ar.n.c.s.* To be able to produce with rapidity and faithfulness repre sentations of such objects and phenomena as are visible in the field of the microscope, is a matter of great importance to the labourer in almost every branch of natural science. Some observers are content to discard all adventitious aid, and to draw from the microscope in the same way as they would from an unmagnified object, relying for success on their own skill as draughtsmen. But though this method LIGHTING THE SITTER. Sib,—I do not wonder at the perplexity felt by those unacquainted with art, at the conflicting statements that appear in the various journals devoted to photography, respecting the lighting a glass room, or in other words, lighting the subject. To artists generally, there can be no difficulty attending it, it being well known to them, that the most beautiful effects are produced by the principal light falling on the object at an angle of 45’, or there abouts, on the side-front. Want of time only, prevented me writing in confirmation of your remarks. No. 3 of the reply to questions put by “ H. G. B.,” in the September 19th number of the PIOTOGRAPMIC News. After thirty years practice in giving lessons in drawing and painting, and in rooms as variously lighted as the residences entered, I am quite prepared to say that a front light will never produce a pleasing effect, any more than light falling particularly from the top will do it. It will be easy for anyone, however uninstructed in art, to satisfy themselves, at the cost of a shilling or two, laid out in the purchase of a moderate sized plaster bust, and placing it where the sitter should be, and trying it in various positions, lighting it in various ways, and occasionally hanging a white blind or sheet at a little distance from the shaded side, to give reflection. It is a pity, with such easy means at disposal, that so much uncertainty should prevail. In a paper I read on the subject, when a member of the Green wich Photographic Society, I illustrated what I am now advancing, by shading in chalk, on a large scale, a ball, a cube, and a cylinder, in three characters of light and shade, viz., front, top, and side-front light ; and it required no other confirmation than comparing one with the other, to show that the light falling on the side-front, at the angle mentioned, was the most pleasing, as well as the most effective. I hope I have been sufficiently plain in what I have written, for, in pity to the bewildered, I would do all I can to help them; and as I think, if one can make himself un derstood, the less verbose the better, I will conclude, hoping the subject will be satisfactorily determined by each one for himself.—Yours truly, Buchanan Smith. Blackheath Park. [We cordially endorse the advice of our correspondent. Let readers try the experiment for themselves. Wherever the attempt is at all practicable, no matter whether in chemistry or art, our advice is : make the experiment, and inform yourselves of the result. But remember, that in matters of art, the eye wants educating. The eye can only see that it brings with it the power to see. But this is a reason for perseverance, careful observation, and art culture; not for indifference or despair.—Eu.] ELECTRICAL THEORY OF TONING. Sib, When we seek for an explanation of many of th® most common, but little understood phenomena attending photographic operations, we find it difficult, if not impossible, to explain them by any known action of chemical affinities or decompositions. Were we, however, to pay more regard to the many careful observations of skilful experimentalists, i would be less difficult to trace a more intimate con- ’ lection, than is at present admitted, between the electrical tod chemical sciences. ; It is to the first of these sciences, that I have long believed 1 Je owe the success of that part of our operations, known as “toning,” in those cases where the tone is obtained by the ‘eposit of a metal, and the facts recently brought forward to your excellent journal seem to me as so many proofs lending to a confirmation of this opinion ; that what we call "toning ” is not, as is usually stated, a process of substitu- fon, hut is really a process of electro-gilding, in which the Sold of the toning bath is deposited by electricity in a "inutely divided state on the ready formed image of Wife silver. This would, I believe, explain the fact that to addition of free acid, or solution containing free acid, Nnews the action of the toning bath, by setting up anew jtoelectrical current, which has been gradually overcome % the addition to the bath of a negative element, for though the bath may appear neutral to such tests as we Assess, experience teaches us that the effect of adding Ukali is not so immediate as the test paper would lead one lobelieve. To point out all the known facts that would appear to lead to a confirmation of this view, would occupy much of your valuable space; but it will be remembered tot with the old hypo bath and the sei d’or bath, in which to acid was rarely, if ever, neutralized, we never had so "any difficulties in toning proofs, to any desired tone or Slour, evidently showing, with recent observation, that the Pssence of free acid in some form is an important element "easy toning, and which will, I believe, be found to arise " the power possessed by acid solutions of conducting Dents of electricity. . The addition of an alkali I take to be simply a means of .Ming or regulating the rapidity of the deposit, for if ., acid be in excess and the gold, consequently, deposited 'to great rapidity, it will be found that the lights as well Ushadows of the proof will become coloured, and this in is where there cannot possibly be any sulphur present. But "there be an alkali present, the deposit will take place only । those parts where the electrical affinities are strongest, 65 on the shadows of the proof, and the photograph will be " c d before the feeble affinities that may exist in the lights Overcome the presence of the detergent.—Yours respect- % E. E. L. । 8—By this theory also we may explain one of the most I blesome amongst the numerous difficulties that beset the M'ss. We well know, from experience, how hard it is to cntain intact the tone and strength of the proof until it I have passed through the process of fixing. C°w, currents of electricity passing through solutions in- wably decompose some small portion of the fluid through I . ey pass into their orginal elements, such action taking MRin the gold solution would set free minute quantities q9xygen, hydrogen, chlorine, &c. Chlorine and silver, # J n g such strong affinities, the small portion of the former 66Dee (and it would be freed in proportionate quantities (| v , ctivity of the bath), would seize on the equivalent of 1 Anea not yet acted on by the toning, which would be in , - atmeasure the lighter tones of the proof, always last to 1 ‘eqed on by the gold bath, and would form with this un- 1 6ov 81 i ? ’ chloride °f silver; and as every photographer now > " 8 chloride of silver being soluble in hyposulphite of , M' Ve can easily perceive why the proof suddenly loses , ■ v,on immersion in the fixing bath. 1 "efemay .observe that this theory does not in any way e with the many suggested or proved causes of
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