The photographic news

• Bandzählung: 13.1869
• Erscheinungsdatum: 1869
• 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-id1780948042-186900000
• PURL: http://digital.slub-dresden.de/id1780948042-18690000
• OAI: oai:de:slub-dresden:db:id-1780948042-18690000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Bemerkung: Heft 545 (S. 73-84), Heft 547 (S. 97-108), Heft 589 (S. 599-610) fehlen in der Vorlage. Paginierfehler: Auf Seite 444 folgt Seite 443
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

April 30, 1869.] THE PHOTOGRAPHIC NEWS. 213 result. It will thus be seen that large-sized plates must be coated and immersed individually. After coating each plate, the lip of the bottle must be cleaned; and, should any sediment be present, it is ad visable to use two bottles alternately. Should the film after a time commence to tear away in the operation of coating, the collodion must be thinned with a mixture of ether and alcohol, which should be at hand. Some operators pour from one bottle and off the plate into another, filtering and thinning the latter before using it for coating again, and this ensures greater uniformity. Before putting the plates into the third vessel, and again upon removal after soaking, it is my practice to give each a quart of water on the surface. When all are immersed, pour away what remains of the collodion, filter the tannin bath into clean flat dishes, and have the drying box and rack at hand. The tannin bath I use consists of— Tannin 15 grains Gallic acid 5 ,, Grape sugar ... ... ... 5 „ Alcohol 1 drachm to the ounce of water. The tannin should be filtered separately before adding the alcohol, otherwise the resinous part would be dissolved. The gallic acid may be dissolved in alcohol or boiling water. Many modifications of the above may be used—some with advantage, as I shall describe hereafter. The plates, after immersion in the tannin bath, should drain, preferably on a rack, and then be placed in the drying box, there to remain undisturbed till dry. I am inclined to consider a good drying box one of the elements of success in a “ dry ” process, the object in view being that the plates should dry quickly, without sudden varia tion of temperature, and out of the reach of dust and light; and, further, that some provision be made for carrying off the vapour. When the plates are dry, the backs should be coated with some pigment of a non-actinic colour. This effec tually prevents blurring under any circumstances. A con venient medium is annatto laid on with a brush. The addition of a little glycerine or sugar prevents the annatto getting too hard when not in use, and likewise renders its subsequent removal from the plate with a wet cloth easy. The use of collodion containing colouring matter as a backing is to be avoided, on account of the difficulty of subsequent removal and of the danger of a portion getting round to the front of the plate. I may mention, in passing, that the backing furnishes a ready means of recording thereon with a pencil or style any circumstances connected with the preparation or exposure of the plate, as a guide in development. The plates, being prepared and stowed away, will re main unimpaired for years, if the ordinary precautions be adopted in keeping them. One difficulty which is sometimes encountered in pre paring collodio-broniide plates consists of a mottled appear ance of the film. This appearance operates the more detrimentally from the fact of the film being equally sen sitive throughout its entire thickness. The fault is not inherent in this process, and various causes have been assigned for it. Its removal may, I think, be effected by one or more of the following remedies:— 1. When thinning, do not use too much ether with the alcohol. 2. Pour on from one bottle and off into another. 3. Pour plenty of collodion on the plate, do not go twice over the same part, and do not keep it on the plate longer than necessary. 4. A collodion containing an excess of the cadmium salts becomes gelatinous, and may produce the evil. It has been suggested by Mr. Bolton and others to use magnesium or to employ ammonium exclusively, but with what success I cannot state. 5. The evil may, doubtless, be corrected, to some extent, in the development, by bringing out the details of the image quickly, and fixing while yet faint and on the surface, and then intensifying with silver. I have alluded to modifications in the composition of the tannin bath. Within certain limits an increase of tannin gives a resulting picture possessing more contrast, while gallic acid confers softness and greater sensitiveness. The grape sugar prevents any tendency which these crystalliz able bodies may have to become brittle, and likewise assists in promoting a speedy development; and they all act mechanically in keeping the pores of the film open, without which the dry film is impervious to the developer, and insensitiveness results. With this latter fact in view, I have been led to try the action of gum on the film, with such favourable results that I strongly recommend its adoption; and, since then, I learn that its good effects have been appreciated by other workers in this process. Four solutions were prepared:— No. 1.—Forty grains gum arabic) to the ounce of „ 2.—Fifteen ,, gallic acid ( water, adding ,, 3.—Twenty ,, grape sugar one drachm of „ 4.— „ ,, tannin ) alcohol. Ten plates, having been coated and washed, were treated as follows :— No. 1.—Original tannin bath, before described. ,, 2.—Twenty-grain tannin solution. ,, 3.—Old tannin bath, washed, and then gum solution. ,, 4.—■ „ unwashed, ,, ,, ,, 5.—Gum solution alone. „ 6.—Gallic acid, and washed. ,, 7.—Old tannin bath, washed, and then grape sugar. ,, 8.— ,, unwashed, ,, ,, and gum. ,, 9.—Old tannin ,, „ then gallic acid, and washed. ,, 10.—Old tannin ,, „ ,, ,, washed, and finally grape sugar. They were exposed consecutively under a pair of stereo, lenses, and developed as nearly as possible under the same conditions. No. 1 developed steadily and well. „ 2 came out slowly and short of detail in shadows. „ 3 quickly and well—not so intense as No. 1. „ 4 quickly and intense. ,, 5 developed rapidly and intensified readily. The gum plates, upon moistening, assumed an opaque, porous, and creamy appearance—developed almost like wet plates, and the deposit was of a peculiar non-actinic colour. The remaining plates developed as I expected— the gallic acid lacking intensity, possibly from over-expo sure, the grape sugar coming out in half the time, and readily acquiring density. I have made a new tannin bath on my old formula, adding thereto 20 grains of gum to the ounce, and hope to report further on another occasion. Meanwhile, I would say to those who have not yet adopted our process—Give it a trial; and to those who have—Try gum. orrespouence. OWNERSHIP OF NEGATIVES. Sir,—In the case of ownership of a portrait negative, the matter seems to me to lie in a nutshell; for when the person desirous of a dozen O.D.V.’s or a cabinet portrait asks what you charge, you tell him, it may be, perhaps, six shil lings, or it may be twelve. He orders (say) a dozen O.D.V,’s. [ You supply him, and, I take it, the matter ends there.