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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
- Lizenz-/Rechtehinweis
- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-186800009
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- http://digital.slub-dresden.de/id1780948042-18680000
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- oai:de:slub-dresden:db:id-1780948042-18680000
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- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Parlamentsperiode
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- Wahlperiode
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- Bandzählung
- No. 530, October 30, 1868
- Digitalisat
- SLUB Dresden
- Strukturtyp
- Ausgabe
- Parlamentsperiode
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- Wahlperiode
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
- Ausgabe Ausgabe 1
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- Ausgabe Ausgabe 613
- Register The Index To Volume XII 619
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Band
Band 12.1868
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- Titel
- The photographic news
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524 THE PHOTOGRAPHIC NEWS. [October 30, 1868. enlargements with very short exposure. The paper is pre pared as follows :— Rain water Tapioca Iodide of potassium .. Chloride of potassium.. Lemon juice .. 1 litre .. 20 grammes .. 10 .. 40 .. 250 drops The tapioca is first made into a paste by pounding in a small quantity of cold water, and the other materials are then added gradually, having been previously dissolved in the litre of rain water, which has been made to boil. It is kept heated during the adding of the tapioca, and until the liquid becomes clear. When cool, it is spread on the paper by means of two pieces of sponge, as in the prepara tion of arrowroot paper. If exposed to the atmosphere, this paper very quickly assumes a reddish hue, and marbled stains often show themselves on the surface ; but these de fects disappear when the sheets are sensitized. The silver bath is composed of— Rain water ... ... ... 1 litre Nitrate of silver .., 60 to 100 grammes Citric acid 5 ,5 The strength of this bath should be reduced if the negative be dense, and increased if the negative be soft. The exposure must be prolonged until the outlines of the picture appear on the sensitive paper. It is then developed in a solution composed as follows :— Rain water 4 ounces Saturated solution of gallic acid ... 1 ounce Immersed in this bath, the proof will there become gradu ally stronger, and will assume a sombre brown tone. It should be raised from time to time by the corners and ex amined. When it has attained sufficient strength it must be taken from the bath and made to float on a water bath, to prevent the gallic acid from sinking into the paper. After some minutes the sheets should be plunged into the water and well washed ; it is then toned in an old gold bath, and finally it is fixed in the ordinary manner. After the mounting the proofs may be treated with encaustic paste or varnished if brilliancy is required. PHOTOGRAPHIC PRINTING IN SILVER, THEO RETICAL AND PRACTICAL. BY W. T. BOVEY.* I have frequently been asked by photographers of tender conscience, how I contrive to tide over the evil which, say they, must arise from the presence of free acid that is borne by the prints from the toning to the fixing solutions. I reply, “If any scruples are entertained, by all means add a little carbonate of soda to the preliminary washing water ; it can do no harm. I doubt its power to effect good ; it may, however, neutralize all the free acid conjured up by your imagination.” In point of fact, it might be set down as a certainty that with the employment of the double salt of gold and sodium, together with an addition of free nitrate of silver to the bath, the toning solution is neutral; at least, with the most sensitive of litmus paper I have failed to detect acidity. Indeed, to add an acid in an appre ciable quantity is to inaugurate disaster. In my own prac tice I simply remove the prints from the toning bath to a tray of water when they are ready for fixing, which last operation demands our next consideration. Concerning the strength of hypo solution to be adopted for the proper fixation of silver prints, a diversity of opinion exists, and, as a natural sequence, each practitioner thinks his particular method the best. At a first glance over the matter it would appear a subject of small importance what strength of solution is adopted, as long as the unreduced * Continued from p. 511. silver is dissolved out of the paper. Nor would it occasion any difference if the fixation of the picture was the only condition to be considered. But allow me to point to an hitherto unrecognized fact, that the formation of blisters is frequently caused by the adoption of a fixing solution of excessive density—in other words, by the employment of an over-dose of hyposulphite of soda. Considering the matter by the light of common sense, has it never occurred to those who advocate such excessively strong baths that they over step the bounds of economy by using an amount of hypo altogether disproportionate to the actual requirements, as the amount of the fixing salt they provide would afford hyposulphurous acid sufficient to combine with a thousand fold more atoms of silver than the prints supply ? I readily admit that to consider only atomic combinations would, under the circumstances, be worse than dangerous, as the resisting power of the albumen and paper has to be provided against. But I contend that at the extreme outside, 3 ounces of hypo to an imperial pint of water are ample for fixing any number of prints that quantity of water can comfortably contain. With a paper weakly albuminized, no fear of blisters— even with the strongest of fixing solutions—-need be enter tained. It is when the albumen surface is raised above the paper by reason of its thickness—when the pores of the paper are sealed and rendered air-tight—it is then, and only then, blistering requires guarding against, and the avoidance of the evil depends on the density of the hypo solution, for the following reason. Up to the moment the prints leave the hypo bath, despite the handlings and washings the prints have been subjected to, they have failed to dislodge minute quantities of air imprisoned in the pores of the paper. Now with a slight coating of albumen, or when a coarse-textured paper is used, the outer portion of each pore remains open, so that, on immersing the prints into the final washing water, a quantity of air-bells forming on the surface of the paper go to prove that air is escaping ; but when that air can find no outlet, it stands to reason that any application of considerable force must separate such portions of the albumen as have no firm hold on the paper. Phy sical science proves that such force exists—a force that finds in the conditions provided by an albumen surface a fitting field for action. The agent in question is allied to capillary action, and is known by the outlandish name, end osmose, which in commonplace English may be interpreted as meaning that when two liquids capable of admixture with each other are separated by any surmountable obstacle, the lighter fluid makes a rush to unite with the heavier. On consideration, it will bo perceived how this force acts on an albumen print. The pores of the paper act as capillary tubes, through which the hypo solution enters as far as the confined air will admit it. So far there is no extra pressure; but when the prints arc removed from the hypo to the washing water, this last makes a rush on the hypo, and the hypo solution gives an extra squeeze to the air, which, in its efforts to escape, dislodges the albumen, and blisters result. The remedy is obvious: reduce the strength of fixing solution, and you do some thing towards removing the difference of density between the hypo bath and water. I have followod up some inter esting experiments in the direction here indicated, andI might say that I have produced blisters at will. Bear in mind I write of albumen surfaces, and on pure albumen surfaces only I experimented. As a wind-up to the subject of the fixing bath, I append the formul I adopt:— Pure hypo 2J ounces Water 1 imperial pint Time of immersion, thick paper, quarter of an hour; thin paper, ten minutes. And now for the final washings. What a deal of fuss ha been made about this and that washing machine I Wha horror of feeling has been experienced when it has been tel , of some careless brother, he puts his prints from the hyB bath direct into his washing trough 1 I freely confess my 861
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