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
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-186800009
• PURL: http://digital.slub-dresden.de/id1780948042-18680000
• OAI: oai:de:slub-dresden:db:id-1780948042-18680000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

270 THE PHOTOGRAPHIC NEWS. [June 5, 1868. First, then, I believe that the importance of perfect dry ing is as yet being only begun to be understood by some of the most experienced dry-plate workers. To this source I am disposed to ascribe the uncertainty commonly attributed to dry-plate work, which uncertainty quite disappears when a perfect method of drying is used. I can say that having dried hundreds of plates by my own method I have never- seen one turn out insensitive. M. de Constant, an experienced dry-plate worker, writes me that he has succeeded in tracing up cases of at first most puzzling non-success to a deposition of dew upon plates transferred from a colder to a warmer and damper atmo sphere. This is the same thing in another form. A dry plate must be dry. And when a photographer takes with him a dozen imperfectly dried plates, and finds spots, stains, and irregular development, he should have known that he was preparing for himself nothing but disappointment. Dry plate work, properly conducted, is singularly free from stains of all sorts. Again, the ordinary methods of drying leail directly to imperfect results, unless, perhaps, where the operator places his plates in an oven, and so applies a steady, dry heat. Few persons, however, have conveniences of that sort, and most photographers will very decidedly prefer to dry their plates in the dark room. This leads directly to placing the plates in a dark closet to dry, a method of the most imperfect character, and liable to several grave objections. First, the whole air of the closet becomes damp by the evaporation, which is consequently checked. The last portions of damp ness are those most difficult to expel, and it is just when the plates have reached that stage that the atmosphere becomes most incapable of finishing its work; in fact, the tendency in such a case is to establish a sort of equilibrium of mois ture, the plates reaching the same stage of half dryness as the air, and then ceasing further to dry. It is not surface dry ness that is wanted, but through and through dessication. Another defect of closet drying is, that the plates are rested on blotting-paper, which keeps up moisture at one end and tends to irregular drying, which is always accompanied by irregular sensibility, leading to unsatisfactory results ; and if the closet be left a little open to change the air, we then run the risk of dust settling on the moist surface. In a close box some of these evils are avoided, but no satisfactory drying can possibly be effected unless there is present a substance that energetically absorbs moisture. So far chloride of calcium is the only substance that has been used ; very few, however, have been willing to use it. It rapidly liquefies, and then must either be rejected as worth less, or else must be evaporated down to dryness, and then be fused in the fire. There is yet another objection to this method, that if a particle of dust of the chloride should get on a plate it would adhere, liquefy, and cause a ruinous stain. I avoid these difficulties, one and all, by the use of sulphuric acid. However inappropriate this substance might at first seem, it works so well as to leave nothing to be desired. Sulphuric acid has long been used in analytical chemistry for dessicating, and it may most advantageously be introduced into photography. The mode of employment consists simply in placing it in a pan or basin in the drying-box. The plates to be dried either have a corner set in one of a series of tumblers ranged round the sides, or else arc set in a frame which is placed in the drying-box. Now, one great advantage of this method is that its cost is absolutely nothing. Sulphuric acid is so cheap, that even if, after it had performed its office, it was rendered worthless, the cost would not be great. But there is not even this drawback. A considerable quantity of sulphuric acid is wanted in the photographic laboratory for cleaning plates, so that the method here proposed for drying works in most conveniently with the method of cleaning with bichromate of potash and sulphuric acid which I introduced some years ago. The sulphuric acid, after it has absorbed so much moisture in the drying-box as to be no longer useful, is as good as ever for cleaning with. As the acid augments continually in bulk, by reason of the water which it absorbs, the photographer will do well to bear this in mind in the selection of a vessel to contain it. Ordinary photographic porcelain pans are not very suitable, even the deep ones, on account of the danger of spilling when they are lifted out. Basins about three inches deep are better. Good porcelain will stand sulphuric acid inde finitely ; bad will not. Glass is excellent; common glass finger-bowls will do very well; several should be placed in the box with half a pound to one pound of sulphuric acid in each. After the acid has swelled to double its original bulk it should be replaced with fresh. Although I had used this method for a long time, and with regular and unvaried satisfaction, I did not care to publish it without making a careful comparative test. Some might imagine that plates which had been in presence of so powerful an acid might, though very well dried, exhibit less sensitiveness than plates managed in the usual manner. To be able to reply positively to any such objection, the fol lowing comparison was made ;— Two plates were prepared under circumstances absolutely identical. One was dried by the new method ; the other was set in a dark closet, resting against a large bottle of very hot water ; after drying, both received an equal expo sure, and were developed side by side in pairs. The plate dried over sulphuric acid proved the more sensitive of the two. It seems of interest to make the remark here, that im perfect drying always diminishes the sensitiveness. For example, the lower end of a plate is always the last to dry. If a plate be exposed before the lower end is dry, that part will be found to give a thinner image than the rest. My own experience points to twenty-four hours as being the proper time in the drying-box. At least I find that if plates be prepared at night, and be used the next morning, there is danger of finding the lower corners insensitive from incomplete dessication. Of course, when plates are dried by heat, the time may be greatly shortened, but I have never liked this mode. When a plate is dried horizontally, spots tend to dry more slowly than the rest, and these cannot fail to show themselves in the development. If the plates be reared up, resting partly on a hot tin and partly on their own edges, these edges need blotting-paper under them, and this must tend to irregular action and cloudiness. Plates dried as here recommended, in a box with sulphuric acid, are very free from all faults that can be ascribed to irregular drying. PICTORIAL EFFECT IN PHOTOGRAPHY; Being Lessons in Composition and CIAROsCURa for PHOTOGRAPITERS. BY II. P. ROBINSON. Chapter XIX. 6 Peculiar toil on single forms bestow, Then let expression lend its finished glow.”—Du Frexiiny. “ We must not omit to speak of the hand as an instrument of expression. Formal dissertations have been written on this ; but were we constrained to such authorities, we might take the great painters in evidence, since by the position of the hands, in conformity with the figure, they have ex pressed every sentiment. Who, for example, can deny the eloquence of th e hands in the Magdalen of Guido; their expression in the cartoons of Raphael; or in the Last Supper, by Leonardo da Vinci ? We see there ex pressed all that Quintilian says the head is capable of expressing. ‘For other parts of the body,’ says he, ‘assist the speaker ; but these, I may say speak themselves. By them we ask, we promise, we invoke, we dismiss, we threaten, we intreat, we deprecate, we express fear, joy, grief, our doubts, our assent, our penitence ; we show moderation, profusion ; we mark number and time.’ ”—Sir Charles Bell. Portraiture—continued. Portraiture may consist in the representation of a single figure, or of a group of persons. We will first consider the composition of a portrait picture in which one person only is represented. Long experience will show that the two sides of every face iffer. This is very evident in many faces, and in all, how-