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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. 220, November 21, 1862
- Digitalisat
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Zeitschrift
The photographic news
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Band 6.1862
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- Ausgabe Ausgabe 73
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- Register Index 619
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Band 6.1862
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November 21, 1862.] THE PHOTOGRAPHIC NEWS. 555 2. lakes ghth dry ■ will pure para- train ite of more con- iht of Id be coni’ this; quire umi* 8'75. er or ture, ising con- sufi- lbu- utity iduce suits Iting find e, is, vorth t the same ving 1 do lbu- it is vey pt di ride; iur is oride ribu- the otiod ially This d al 111 and izing itiOOi coD- hi»S not olain cod- base the acies will lon 1S ndef s re- been as of * No. 13, pag c ,-,23. aldthat it cannot be, and never is used in albumenizing Aaper; however, the opinion that the nitrates do, in some ay or other, affect the colour, appears to be daily gaining pound; if it were not so, why the use of two chlorides ? Those who use barium in conjunction with ammonium, do ’’because they say it renders the tone blacker; and, as far Mmy own observation goes, they say so with truth ; but what Possible effect does a modicum of chloride of sodium have, ’ken added to that of ammonium ? I fear, that if those who •bus employ it, were asked their reason for so doing, their ply answer would be, because they thow/hi it had some ■feet; but they could not tell you what had induced the klief. J hi Mr. Hart’s Formula: (Bourquin’s Albumenizer)* we find '’t grain in every eight is chloride of sodium ; this substi- ttion of one grain, cannot be because it is an easier way of Cueing the quantity of chloride of silver, than by taking "s equivalent of ammonium ; as the reduction, by using one Pain of chloride of sodium instead of ammonium is only ’■15th of a grain, which is but l-80th of the quantity that "ould be produced by eight of ammonium. If the chloride “sodium be employed with the idea that the nitrates affect ecolour, the nitrate of soda must be believed to have a ypowerful colouring property. Taking the atomic weight iehloride of ammonium at 54, nitrate of ammonia at 80, tloride of sodium at 60, and nitrate of soda at 86, I find le nitrate of soda is but the 38Z,th part of the conjoint itrates. chemical comtnnation with the albumen? 5th.—Are there two separate compounds of silver formed by sensitizing a chlorided albumenized paper, viz., the chlo ride and the albuminate, and do they act independently of of each other ; or, is one joint compound formed? if I may use such an expression. It is, perhaps, scarcely necessary to say, that reasons should be given for the holding of an opinion upon these subjects, and not mere assertion, even though it be backed by the authority of names well known to fame. I have lived long enough to have learned that it is unwise and un safe to accept as facts the assertions of any man, hoxcever high may be his rank in the particular art or science which he has made his study ; and very many of your readers can no'doubt supply, from their own reading, numerous instances where a thing has been declared upon high scientific autho rity, to be either an impossibility, or not the truth, which almost every little, ragged, uneducated urchin now knows to be a fact. The chloride of sodium, is said to give a cold tone, and Gat of ammonium a warmer one; we can, therefore, easily Anagine how, if any preference be given to sodium for any p 1 ® whatever, that an equal quantity of chloride of ammo- Im added to it, may render the tone perceptibly warmer, ind yet not destroy the particular colour it may give, as in larion’s formula ;t but I must candidly confess my own ability to conceive the good of one of sodium to seven of Smonium, and strongly believe that the addition is more , \ frncied improvement than a real one. When the chlo- of barium is used in conjunction with that of ammo- m, it has, in every case coming under my cognizance, n in equal proportions, as in Maxwell Lyte’s formula.]; .The theory which attempts to explain the formation of I " image, by the decomposition of the chloride of silver, I 44 the recomposition of additional chloride by the libe- Bted chlorine seizing upon the silver in the free nitrate, is ed upon the manner in which chloride of silver acts when in totally different circumstances to what it is in Pitive printing. It is well known that altered conditions many cases produce totally different combinations ; are • 'then, warranted in holding this theory, when in print- p the circumstances are that a mere film is formed and M on a sheet of paper, which film is said to consist of Uloride of silver in conjunction with the albuminate, and ph the addition of free nitrate; the said chloride is, /"’fore, placed under peculiar conditions. Has it ever been । ^'ed that the chloride and albuminate of silver produced 1 Sensitizing a chlorided albumenized sheet of paper, arc in „lity two separate compounds, and not a double, salt, "ich for distinction’s sake I will term the chlor-albumi- In taking leave of the subject for the present, I can only I that should I even be proved to be wrong in every tticular respecting the tables I have given, and it should qdlead to a profitable discussion, by which a single fact is nded to our imperfect knowledge, I shall console myself |the words of Burke, who tells us, that “ a man who works eond the surface of things, though he may be wrong him- ty ’ Yet clears the way for others, and may chance to make Ahis errors subservient to truth.” | flow me, in conclusion, to recapitulate the subjects which h t ' ln ^ worthy, of discussion, and on which I invite your ous talented readers to give an opinion. PHOTOGRAPHIC PORTRAITURE. BY M. arc. A. GAUDIN. Photographic portraiture has become an important branch of industry, which improves daily, amid a host of difficulties which still prevent its attainment to perfection. These difficulties are of many kinds; the greatest are those resulting from duration of the sitting, which does not yet permit of our rendering that instantaneous expression, without which life cannot be manifested. From this im possibility of rendering instantaneous expression, it happens that the most satisfactory portraits are those taken in profile, where the eyes are fixed on an object, a portrait with a natu ral expression is obtained, which photography, in its present state, renders in perfection. But the public desires something more than this, it requires a “ full face ” portrait, without shadows, which accumulates all the difficulties of the artist operator. For the present I shall say a few words about a fact which is not usually taken into account, but which acts with more or less intensity everywhere; it results, from this general principle, that photography operates under the influence of the invisible chemical rays rather than under the influence of the rays most luminous in appearance. Thus it is that light loses a great part of its photographic power by simply passing through a sheet of very thin glass. By an analagous reason, reflected light never produces a photographic effect in proportion to the light it sends to the eye. For example, if an operating room be entirely hung with yellow, red, or green drapery, the greater luminousness resulting from the employment of yellow drapery, in proportion to that result ing from green, would lead us to believe that much greater rapidity of exposure in the camera might be obtained from the yellow than from the green. Experience, however, does not confirm this hope; with the employment of draperies of these three colours, the chemical rays of light will be almost wholly absorbed; only the direct light will be efficient, consequently the model will be wholly deficient in chiaroscuro. Unless then, the operating room be hung with white, or, better still, with light blue drapery, to diminish the day light, I say that the photographic picture will never repre sent the model as it appears to the eye, in consequence of the transformation of the reflected light, which greatly increases the intensity of the shadows, and this is partly 1st.—Which of the three compounds of silver plays the most important part in positive printing upon albumenized paper ; the chloride, albuminate, or free nitrate. 2nd.—Is the free nitrate of silver a principal, or only an accessory in the formation of the image ? 3rd.—Is the enormous excess of free nitrate of silver, indicated in Table No. 2, necessary I and if so, why? 4th.—Is the albumenizing solution a mere mixture albumen and chloride, or does the chloride enter into a f No. 14, p. 522. + No. 6, p. 522.
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