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The photographic news
- Bandzählung
- 29.1885
- Erscheinungsdatum
- 1885
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- Englisch
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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. 1395, May 29, 1885
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 29.1885
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- Register Index III
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Band
Band 29.1885
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May 29, 1885.] THE PHOTOGRAPHIC NEWS. 341 fication anl reduction combined,” some may say; “ why the one is the reverse of the other, and undoes it—addition and substruction, multiplication and division—they negative one another.” It is very easy to show, both experimentally and theoretically, that probably in every case reduction does not simply reduce, and that unless special precautions are taken, intensification does not simply intensify ; but that in both cases the proportional density of the negative is changed, and its character is therefore no longer the same. This change of character in a plate is very annoy ing unless appreciated, but it gives the photographer a power that many are not aware of. If we intensify by putting two particles of silver where- ever one exists, or by changing every atom of silver for an atom of mercury or a proportional amount of any sub stance that is more photographically opaque, then we get a simple case of intensification. By such an operation the density is increased, but the proportional densities are not changed, so that the character of the plate is not changed. Suppose, for instance, that the densities of the original negative are represented by the figures 1, 2, 3, 4, 5. the densities on the intensified plate may be 2,4, 6, 8, 10, or 3, 6, 9, 12, 15 ; an increased range of density, but the pro portions unchanged. This simple intensification can only be produced (the writer believes) by causing the intensifier to act right through the film—that is, the intensifier must act till its action is complete. A proportional reduction must also act right through the film, and so entirely remove theimage ; any reduction short of this is not proportional— that is, the densities do not bear the same ratio to one another that they did before the operation—and so the character of the negative is altered. It is obvious that in the development of a gelatine plate the image is produced first on the face of the film, and penetrates tothe back more or less according to the density of the part. The detail in the shadows is the last to appear, and penetrates ihe film to a less extent than any other part of the image, so’that we may consider the densities referred to above as in the figure which represents a section through —1,2—34 5 ------ -- “ 3%529*6wta — ■ --“SSE“Zggg"-.. Class the film. Any solution that acts upon the image will pro duce its effect first upon the surface of the film, and then gradually through it according to its penetrating power. If a single solution intensifier is used which can give a double density, by the time it has penetrated one-fifth through the film, the part marked 1 will be fully intensi fied to a double blackness, but the part marked 5 will be increased in density only to the extent of one-fifth, and the numbers which represent the densities will be 2, 3, 4, 5, 6, instead of 1, 2, 3, 4, 5. The effect (if the negative had no clear glass) would be much the same as if a sheet of translucent material were put over the negative: print ing wouldbe retarded, and the resultingprint not improved. But if the intensifier penetrates two-fifths through the film before its action is stopped, a further intensification takes place except at the thinnest part, and the resulting densities read 2, 4, 5,6,7; that is, an increase of contrast in the thin parts, the shadows, but no increase of contrast in the denser parts, the lights; and this effect has been produced without any local application of the solution. If, therefore, it is desired to intensify so that the pro portion of densities shall not be changed, the intensifica tion must be thorough, and a reagent must be selected that will, after thorough action, give the required amount of intensification ; for example, the uranium intensifier is useless for producing a slight effect. But, on the other hand, if a negative has been produced of (say) a castle and foliage, and the detail in the foliage is buried in printing before the detail of the castle is sufficiently brought out, a short application of the uranium intensifier will probably improve matters, by giving more vigour to the foliage, without appreciably altering the denser parts of the nega tive. Sometimes the local application of the intensifier by means of a brush is vastly superior to the use of tissue paper, because the intensifier not only retards print ing like the tissue paper, but also gives more vigour. Reducers, of course, can never be allowed to act tho roughly, or the image would be entirely removed ; unless, indeed, the reducer be of such a sort that it merely alters the colour of the image. One would expect reducers to cause increased contrasts, and certainly they do so unless their action is prolonged. The reducer acting from the surface will remove the uppermost layer of the image, so that the detail in the shadows may be even entirely dissolved away, while the chief effect upon the rest of the negative is, that it will print more rapidly. One may often, by suitable reduction, remove a general fog without injuring any detail of the image. By a suitable combination of reduction and intensi fication, many improvements may be made. For example, two negatives of the same subject were sub mitted to the writer, both fogged, but one much more fogged than the other, and at the same time less dense in the shadows. This negative, the thinner more fogged one, he intensified with mercury and sulphite and then reduced with potassium cyanide, and by that means produced a plate with very much less general fog and greater density in the lights than the originally better negative. The intensification was done first for two reasons ; it avoided the use of hypo with the troublesome washing, &c., that it involves ; and there was no fear of getting the detail in ths shadows so thin that the intensifi cation could not give enough density. It is no doubt possible to modify the results indi cated ; but one cannot doubt the truth of the princi ples laid down. It is a grave mistake to work for density at all hazards, trusting to reducers to give what is required. Intensifiers and reducers are not the handy, universally useful reagents that the rule-of-thumb photographer con siders them to be, though when used intelligently they will produce effects perhaps not attainable in any other way. FRENCH CORRESPONDENCE. M. BALAGUY’s Carbonate of Soda Developer—Prin ciples or AXTIPLANATIC Lenses—Gelatino-Chloride of Silver Paper—Typographic Printing Block or a Fusible Alloy—Trades Exhibition—M. CHENXE- VIERE’s Pellicle Dark Slide—Banquet or the Photographic Society or France. M. Balaguifs Carbonate of Soda Developer.—M. Balaguy has made some very conclusive experiments on a developer with carbonate of soda (common soda) as basis. The following solutions are made :— No. 1.—Water Carbonate of soda No. 2.—Water Sulphite of soda ... No. 3.—Pyrogallic acid ... Alcohol at 40 per c ... 1 litre ... 200 grammes ... 250cubic centimetres ... 50 grammes ... 10 grammes ... 150 cubic centimetes Take 250 c. c. m. of No. 1 solution in a bottle, and add 2 grammes of bromide of ammonium. For instantaneous pictures pour into a glass— Water ... ... ... ... 50 c. c. Sulphite of soda solution 5 „ Pyrogallic acid ,, 5 „ Moisten the plate for a few seconds with this solu tion, then add in the glass 10 c. c. of the non-bromised soda solution and 2 c. c. of that containing bro mide. Mix well together, and pour the whole over the plate. Should the image be slow in showing
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