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

54 THE PHOTOGRAPHIC NEWS. [May 28, 1869. purpose. Stir the mixture now with a glass rod, cover the jug with a plate, and leave it until quite cold. Immediately the water and acid are mixed, great heat is evolved, and the necessity for taking the above precautions will he at once evident, since any breakage of the vessel through the sudden and great heat to which it is subjected will be attended with the most destructive consequences to almost everything that the acid touches. Have ready three perfectly clean dishes arranged side by side. No. 1 must be of good porcelain, quite dry, and in size about 10 by 12 inches. Nos. 2 and 3 should be very deep, and holding not less than half a gallon each. Into No. 1 pour the mixture of sulphuric acid and water. Nos. 2 and 3 must be filled with pure water, and into the latter a few drops of solution of ammonia must be added. Now take the photograph (which must be quite dry), and, in the ordinary way, lay the picture side on the acid, taking great care to avoid air-bubbles; then instantly lift it up, and lay the plain side on the liquid. This will not be at all difficult, as the wetted surface curls slightly inwards^ the acid producing an opposite effect to that of water. Any part which is not covered with liquid is now to be gently pressed under with a glass rod or platinum spatula, and the sheet left immersed in the acid for a space of time varying between a quarter of a minute and two minutes, according to the kind of paper on which the picture has been printed. Canson’s thin paper will require about thirty seconds; Canson’s thick, one minute; thin papier Saxe, twenty seconds; Whatman’s and Turner’s, about ten seconds, if the size has been well removed; but if they still remain non-absorbent, two minutes will not be found too long. After the sheet has soaked for the proper time, gently raise one corner out of the acid, and, guarding the thumb and finger from in jury with a double fold of blotting-paper, lift it entirely out by means of this corner, and allow it to drain for a few seconds; then, with a quick motion, completely immerse the sheet in dish No. 2, and move it about in all directions, so as to remove the strong acid from the surface as rapidly as possible. Lift it perpendicularly out of the liquid, and plunge it in again two or three times consecutively, and then transfer it to dish No. 3, where allow it to remain until the whole number of sheets are completed, or it becomes incon veniently crowded. Dish No. 2 must be emptied and refilled with pure water, after about six sheets have been passed through it; and in dish No. 3 a piece of good blue litmus paper should remain, and as soon as this shows the slightest tendency to become reddened, a few drops of ammonia must be added, and the whole mixed well together; for if any, even the slightest trace, of unneutralized acid remain in the paper after coming from this bath, the picture will soon be inevitably destroyed; thus the necessity of keeping the liquid in dish No. 3 alkaline will be evident; at the same time experimentalists must not forget that long soaking in ammonia is prejudicial to the half-tints of the picture, and thus the excess of alkali must be but small. After coming from the ammonia bath, the sheets will want wash ing two or three times in clean water, and they can then be dried in any convenient way. The paper, when dry, will have an uneven, crumpled appearance, and will require either to bo carefully mounted or passed between rollers, to render it smooth again. THE USE OP INDIA-RUBBER IN PHOTO GRAPHY. When the common use of india-rubber as a mounting agent was advocated a year or two ago, we expressed a doubt as to whether the advantages promised would counterbalance the probable disadvantages involved in its use. Since then wc have given the subject careful attention, and have devoted to it considerable experiment and observation, in order to arrive at a certain conclusion. We have, from time to time, in answer to queries, felt it our duty to warn our readers against relying upon india-rubber as a safe mounting mate rial, and all subsequent experience has confirmed our con victions on the subject. It is certain, we think, that india-rubber is not a trust worthy material for mounting photographs; and, notwith standing its convenience as an aid to attaching prints in scrap-books and albums without risk of cockling, and the aid to permanency promised by its advocates in virtue of the waterproof character of the layer of cement, we think it unwise to use this material for mounting photographs in tended to last a dozen years. We have prints in our pos session which have been mounted with india-rubber some thing less than two years, which show no signs of deteriora tion ; but we have also some which, in the same period, have curled away from the cards. We cannot find one which has been mounted with this material for a dozen years which has not deteriorated and left the mount, leaving a brown, non-elastic, friable layer on thecard. Mr. Spiller— who, as our readers know, has given a good deal of atten tion to the effect on india-rubber by light and air, which he reported very fully to the Chemical Society a few years ago—recently called our attention to his experiences with india-rubber as a mounting agent, by which our own views are most fully sustained. In every instance in which his prints of some years ago were mounted with india-rubber, the elastic gum was changed into a brown, friable resin, facilitating decay rather than securing permanency. The change was found to be precisely of the same character as that he had formerly found in the thin india-rubber felt used for cartridges at Woolwich. A brief communication on the subject will be found on another page. Another important question arises in connection with this subject. If india-rubber is a perishable substance for mounting, is it safe as a preliminary coating for dry plates? It must be admitted, we fear, that it is doubtful. Bub at the same time, it must be conceded that the conditions under which it is used as a preliminary coating to those which obtain in relation to its use as a mounting material. In the latter case a sensible body of it is used ; however little may be used, it is applied in the form of a paste, and an appreciable layer must be present to secure adhesion; and it is, moreover, never protected from atmospheric action. When used as a preliminary coating for plates, the amount used is infinitesimally small, a solution containing one grain to the ounce being generally employed. It is protected from atmospheric action by the film of collodion and the final coating of varnish ; and oven if it finally change to a friable resin instead of an elastic gum, being on a rigid plate of glass the change would not necessarily be mis chievous. Except, therefore, the scarcely appreciable amount of injury which might result from the trace of india- rubber darkening under the action of light, we do not see any reason to anticipate serious results from the use of india- rubber as a preliminary coating to dry-plate negatives. As a layer forming part of a transferred negative, its dis use has already been recommended by Mr. Woodbury, and it is manifest that any change in a layer of india-rubber occupying such a position might be destructive of the nega tive. To protect the negative film from the action of the solvents in the coating of leather collodion applied as a means of transferring the negative, and supporting it after a film of india-rubber, seems at first sight the best possible appliance, as it not only so protects the film from the sol vent, but gives support and elasticity afterwards. But if, however slowly, the india-rubber be gradually changed fiom an elastic gum into a brown powder, it is clear that the value of the negative is much impaired, and its safety seriously perilled ; and that the risk of such a possibility is sufficient to destroy all confidence in the use of india-rubber in transferring negatives. EXHIBITION OF PHOTOGRAPHY, NATURE PRINTING, AND CHROMO-LITHOGRAPH Y IN GRONINGEN. We have received from the Committee of the Photographic Exhibition to be held in the Netherlands the following details, which will interest intending exhibitors. We may remark, that the liberal list of medals, and the facilities offered to English exhibitors for having their contributions forwarded without cost and trouble, afford inducements which will, we hope, be accepted by many of our readers, so that a good and creditable display of English photography may be made. The Committee for the Exhibition, referring to the articles 5 and 14 of the programme, has the honour to communicate to those interested— 1. That the Jury is composed of the following members:-. Mr. F. de Witt, Member of the Town Council, Groningen; Dr. M. Salverda, Professor at the University, Groningen; Dr. L. Ali Cohen, Sanitary Inspector, Groningen ; Dr. E. J. Asser,