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

THE PHOTOGRAPHIC NEWS. Vol. XII. No. 534.—November 27, 1868. CONTENTS. PAGE Fogging of Developed Prints.—New Remedy 565 Amateur Criticism 566 Posing, Phrenologically and Psychologically Considered. By John Beattie 567 Rapid Development Printing Process. By J. W. Waterhouse 568 Experiments, Intentional and Otherwise. By Ed. Seeley 668 Photography in Upper Egypt. By Dr. Vogel 569 Pictorial Effect in Photography. By II. P. Robinson 570 On a New Series of Chemical Reactions Produced’by Light. By John Tyndall, LL.D, F.R.S., etc, 571 Micro-photography. By M. Jules Girard 572 On the Formation of Peroxide of Silver by Ozone. By M. F. 572 Correspondence—Photographers’ Relief Fund—Amateur Criti cism—Proportion of Salt in Albuminized Paper—Paper turning' Brown on Development—Mr. Bovey’s Method of Toning—Portraits upon Graves—Printing Formula 572 Talk in the Studio 575 To Correspondents 576 FOGGING OF DEVELOPED PRINTS.—NEW REMEDY. We have recently been engaged in some experiments for the prevention of fog, or the general browning of the paper during the process of printing by development, and, so far as we can at present judge, the remedy we propose promises the highest success. The fogging of paper prints during development is by no means uncommon. On another page we print a letter which describes this difficulty in a form not unfrequent, we believe, with begin ners in this mode of printing; the example accompanying the letter being one of a class which often reaches us, with anxious enquiries for a remedy. The print, instead of possessing pure lights and deep shadows of brown or black, possesses dull-grey whites and weak-brown shades, whilst by transmitted light the whole presents a mottled- brown effect. The silver salt, in short, instead of being reduced in the exact ratio of the action of light in forming the image, is reduced in some degree throughout the whole of the paper, and a dirty, foggy, imperfect picture is the result. Before proceeding to speak of our experiments, we men tion two or three of the most common causes to which this defect may be referred. One of the most frequent is the action of diffused light. It is difficult to bring the novice who has been accustomed to the ordinary process of print ing fully out, in which the action on the paper of a feeble light is not regarded, to believe that in printing by deve lopment, light should be as carefully excluded from the prepared paper as from an excited collodion plate. And hence a little white light being permitted to reach the paper at some stage of the operations, degraded whites or general reduction is the result. It is probable that the corre spondent to whose letter we have referred, who is an expe rienced and ingenious photographer, would scarcely neglect proper precautions in this respect, and, indeed, an example of good results, obtained by the same formula as the failure, suggests that no white light had been permitted to enter the dark room in its production. But there are two or three causes to which the defect in question may be due. In the first place, the formula employed, whilst it is one which will doubtless give great sensitiveness, is one which will also very readily give fog the moment any of the conditions necessary to success cease to be present in the precise form. Uis paper is prepared with a salting solution containing about 17 grains of iodide of potassium, and under 6 grains of bromide of potassium in an ounce of water, and excited on a 60-grain nitrate bath. There is no acid in either the salting or exciting bath. Compare this with a formula recently given in our pages, described as giving very rapid and excellent results. In the latter formula we find the salting bath contained about 4} grains of iodide of potassium and 18 grains of chloride of potassium, together with 7 or 8 drops of lemon-juice and 9 grains of tapioca, in an ounce of water; whilst the silver bath, which is a little weaker than our correspondent’s, also contains about 5 grains of citric acid to each ounce. In the latter formula everything tends to lessen the chances of fog or abnormal reduction— the decreased quantity of iodide, the large proportion of chloride, and the free use of citric acid. The comparison of the two formula; will be so suggestive to all working in this direction that we need not enter into lengthened comment on the matter. Another cause of this fog, or abnormal reduction, arises from the paper being kept after it is excited. It is always desirable that paper should be exposed and developed as soon after exciting as possible. Most printers are fami liar with the fact that in any kind of excited paper which is long kept there is a tendency to decomposition in the compound formed between silver and the size of the paper, and if this decomposition be only incipient, it will inevi tably be completed in the process of development. Another cause of discoloured lights, and a general dirty yellow, mottled effect being produced throughout the print, is imperfect fixation. Either from carelessness, or with a view to improve the tone, some photographers place the, developed print in the hypo at once, either with very little washing, or none at all. If the hypo be weak or old, the paper, saturated with nitrate of silver and gallic acid, causes a decomposition in the hypo, which sulphurizes the print, or, worse still, leaves it with undissolved hyposulphite of silver in the body of the paper, which, decomposing, pro duces the dirty yellow, mottled effect familiar to some who have failed in enlarging by development printing. The remedy for some of the defects we have mentioned is obvious enough : it is simply to avoid the causes we have indicated as operative in producing the defects. There is a remedy for the fog caused by neutral and excessively sensitive conditions, which, in relation to development printing, has never, we believe, been suggested, but which, from recent experiments, we have reason to think will be very effectual, and will especially meet the case of the correspondent whose letter appears on another page. His especial difficulty is that the same conditions which at times give him perfect prints, at other times—without, so far as he knows, any change in causes—yield only fogged prints. We have repeated the experiment, and have been able to produce at will, without any change in the materials used, either clean prints, or prints utterly fogged, and have traced the cause and remedy. The cleanness or fogging depends on the presence or absence of an unconverted haloid salt in the paper. If the paper be floated sufficiently long on the silver bath to con vert the whole of the iodide or bromide into silver salts, the