The photographic news

• Bandzählung: 29.1885
• Erscheinungsdatum: 1885
• 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-id1780948042-188500006
• PURL: http://digital.slub-dresden.de/id1780948042-18850000
• OAI: oai:de:slub-dresden:db:id-1780948042-18850000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

550 THE PHOTOGRAPHIC NEWS. [AUaTST 28, 1885. “ The average of the highest figures of all the plates developed by the develcper’s table No. 1 is 20'81. In table No. 2 it is 20'80. In table No- 3, 21'56. “ It will be seen here that there is really very little difference between the average figures got from the three tables —that is to say, that the result of altering the quantity of pyro is neither to increase nor to decrease detail to an appreciable extent. It has, however, as I have already said, when increased, the effect of causing development to take considerably longer. In other words, pyro acts as a retarder, not as a restrainer. My impression on first looking at the plates was that those deve loped with the larger quantities of pyro showed a little less detail than the others ; but this general impression is shown by the precise figures given to have been wrong. “ The other averages that I have worked out are not the results of the one of absolute quantities of ammonia and bromide, but of relative quantities. Thus, I have taken all plates deve loped with ammonia and bromide in equal quantities of ammonia and bromide in the ratio of two to one, and so forth. The results are as follows :— “With bromide 4, 1, the average figure is 17'66. With bromide 2, ammonia 1, it is 19. With bromide and am monia equal, it is 20'66. With bromide 1, ammonia 2, it is 21'72. With bromide 1, ammonia 4, it is 22'23. With bromide 1, ammonia 8, it is 22-16. With bromide 1, ammonia 16, it is 21'33.” It will be seen that here detail increases very decidedly till the ratio of ammonia to bromide becomes as 2 to 1. It then farther increases slightly between that ratio and the next—viz., 4 to I—after which it falls off with farther relative increase of ammonia. It will, of course, be understood, that the figures given are relative, not absolute. Thus, under “ ammonia 1, bromide 2,” are included plates developed with quarter grain bromide and half minim ammonia, those with half grain bromide and one minim ammonia, those with one grain bromide and two minims ammonia, and those with two grains of bromide and four minims ammonia. The total increase by altering the ratios of bromide to ammonia from four bromide to one ammonia, to one bromide four ammonia, will be seen to be less than five figures. Cer tainly an amount of compensation for over-exposure—-which the thing practically resolves itself into—is less than I should have expected. Having got out so much more than I expected by developers when the ratio of bromide was so high as compared with ammonia, I tried the effect of developing for a great length of time with the following somewhat peculiarly constituted developer :— Pyro J grain Bromide ... ... ... ... ... 4 grains Ammonia ... } minim Witter up to 1 ounce This developer was allowed to act for the whole night on a plate exposed with the others, at the end of which time the figure 20 was visible, and the density was ample, although the image was of a peculiar orange-brown colour. You, in America, have led the way in the adoption in practice of various alkalies, besides the caustic ammonia, still, as I have said, almost universally used here. I tried a set of experiments some time ago, using caustic soda, caustic ammonia, caustic potash, and the three corresponding carbomates. I failed to perceive any particular advantage in either the caustic potash or the caustic soda. In fact, after giving a very fair trial with various brands of plates, I concluded that, if a caustic alkali is to be used, it had better be our old friend, ammonia. The carbonates, on the other hand, offer, in my experience, a very great advantage for certain work. It is more easy by their use to get density cr pluck than with ammouia. On the other hand, they are considerably slower in their action. One, for example, who has been accustomed to the use of ammonia, and who adopts carbonate of ammonium, is likely at first to conclude that from the carbonate no good will come at all. By the time that development would have been complete with am monia, the carbonate has produced only a thin phantom image of the highest lights of the picture. It is, however, extra ordinary how steadily density continues to increase with the carbonate, till, before long, it has become greater than could have been got with ammouia through any length of time. Of course, in many cases, it is no advantage to be able to gain excessive density. For example, where slow plates aroused on lan iscape subjects, and in portraiture with suitable plates, density is, as a rule, gained with the greatest care, using ammonia, and I can sec no particular use in replacing it with the carbonate. It is when we have to use plates of excessive rapidity, for instantaneous or other work, when, as all know, the difficulty in getting density is usually the greatest we have to contend with, and when subjects deficient in contrast have to be treated, that the carbonates become useful. The following are the relative quantities of the three car bonates mentioned, which are necessary to produce solutions of the same alkalinity : — Sodium carbonate (cryst. as washing soda) ... 1'0 Potassium carbonate (cryst.) ... ... ... 6'1 Ammonium carbonate... ... ... ... 3'36 Using of the washing soda 25 grains to the ounce, and of the other carbonates quantities giving the same alkalinity to the solution, I found sodium carbonate to bo considerably the most rapid in its action ; next to it potassium carbonate, and slowest of all ammonium carbonate ; that is to say, using in each case no restrainer at all. The ultimate density which could be gained I found to be inversely as the rapidity of development; that is to say, the slow carbonate of ammonium would, if time was allowed, give a denser image than any of the others. For this reason I prefer to use it when I use a carbonate at all; that is to say, when I know that with ammonia there will be difficulty in getting density. I fear that I am making a statement which will appear hereti cal to some of you when I say that Icu recognize no advantage arising from the use of any additions to the developer beyond the simple pyro and carbonate of ammonia, except such small quantity of acid as may be necessary in the pyro stock solutions to preserve it. It is true that by using sulphite of soda, sulphurous acid, or one of the various other substances which have been from time to time recommended, 1 might be able to dispense with the alum baths ; but I very considerably prefer the slightly greenish image got by the use of the simple pyro and carbonate developer, followed by the alum bath, to the pure black image got when sulphite is used. As I have said, I believe a better print is got, and one reason of this is, I believe, that without the sulphite a greater range of light is correctly registered on the film. BED PRINTS FOR THE DRAFTSMAN. An innumerable quantity of red photographs are made daily in the city of New York. These red prints are termed silver prints, and although they in reality do not deserve to be called silver-prints par excellence, there is a certain reason or excuse for that generally adopted name. Hardwich’s theory of substitution—-that is, gold substituting the silver of the photograph in the toning process—Moes not find any application here, as the prints in question are simply silver proofs, fixed, without being toned, in a pure and plain solution of hyposulphite of soda, washed, and dried. A majority of the illustrations of our daily newspapers, trade journals, price lists, and various other publications, when printed on the ordinary press from relief plates or zinc etchings, have for a base the photographic silver, or red prints. Such prints, taken from the ordinary negatives, are placed in the hands of a drafts man, who reduces the photographic half-tone, or stipple—in fact, breaks up the original photograph into a system of lines, de stroying its original character altogether. The photograph, having so far served the purpose of being a sketch to the finished picture, is now removed from the paper. A strong solution of bichloride of mercury is poured over it, and in the manner of the so-called magic photographs, the silver deposit on the paper is bleached out, leaving visible only the India ink work upon a white ground. Such pictures are, or ought to be, a correct representation in like manner of the photograph employed. In portraits the likeness can be kept well, and in landscapes, in machinery, and other inanimate objects, the most intricate details can be rendered sharp and distinct as in the original photograph. The drawing in its present condition is handed now again to the photographer, who reproduces from it a negative of ex tremely strong intensity, fit to make from it a relief plate, or to print it on a bichromated albumen or asphaltum film upon a zinc plate, preparatory to the etching process.