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

November 18, 18G8.] TRE PHOTOGRAPHIC NEWS, 547 The cause of these variations in the results obtained are not in any way to be traced in a scientific manner by analysis or otherwise, and we have, therefore, no remedy but that of patiently bowing down before our tormentor. It is not my intention on the present occasion to make known an infallible remedy for the cure of this evil, which we all bear with more or less resignation ; I desire only to indicate to my readers a method which has done me good service from the first, in order that any one who wishes to experi ment with the same may do so if he deem it sufficiently worthy of trial. My collodion is a compound of three collodions. No. 1 is made up of the undermentioned ingredients :— Rectified ether ... ... ... 70 grammes Alcohol... ... ... ... 30 „ Gun-cotton ... ... ... 1 gramme Iodide of cadmium ... ... 0-5 „ Iodide of ammonium ... ... 0-5 „ Bromide of cadmium ... ... 03 The above formula produces a liquid and perfectly colourless. No. 2 is thus compounded:— Ether ... Alcohol Gun-cotton Iodide of cadmium ... Iodide of ammonium .. Iodide of potassium ... Bromide of cadmium ... Bromide of ammonium of thick consistence, GO grammes 40 1 gramme 0-5 „ 05 „ 0'3 „ 0-2 „ 0-2 A small quantity of sublimed iodine is added sufficient to give a pale yellowish tint to this collodion, which is more strongly iodized and bromized than the former, and likewise more liquid, on account of the large proportion of alcohol which enters into its composition. No. 3 collodion is thus made up :— Ether ... ... ... ... 55 grammes Alcohol... ... . ... 45 „ Gun-cotton ... ... ... 1 gramme Iodide of ammonium ... ... 0'8 „ Iodide of cadmium ... ... 03 „ Bromide of ammonium ... 0 5 ,, This last formula resembles that of M. Inglis, which is a very quick-acting material; it is indispensable for the pro duction of children's portraits, so beautiful when they prove successful, so detestable when they are failures. The mixture of these three collodions is made at the time of their employment, equal parts of each liquid being taken, excepting when working under certain conditions, as every photographer will understand. Thus, in very cold weather, a somewhat larger proportion of No. 1 is used, which contains one-third of alcohol to two-thirds of ether; in very hot weather I augment the proportion of No. 2, in which the large amount of alcohol prevents the too rapid evaporation of the ether; and finally, in dull and rainy weather, or when children are to be photographed, the pro portion of No. 3 is increased by reason of its greater rapidity, and of the larger amount of bromine in its composition. It is regarded by many as a foregone conclusion—without, indeed, the existence of any absolute proof—that bromide of silver is more sensitive to weaker rays of light than the iodide of the same metal. Everybody may have his own opinion on this subject, pending a positive solution of the problem : and wo are inclined to believe that the sensitive ness is due solely to the presence of iodo-bromide of silver with an ammoriacal base, produced by means of a double decomposition. The third formula employed by itself presents all the characteristics—both advantages and dis advantages—displayed by preparations in which iodide of ammonium predominates. Eor the purpose of comparison in a practical manner, I prepared a collodion of the pro portions above indicated, so as to participate equally in the three formula), but the liquid thus obtained yielded unsatis. [ factory results, whereas a mixture of the three compounds prepared separately continued to work wonderfully. The explanation of the fact I have mentioned reminds one of the elaborate scientific researches which have been made for the purpose of obtaining wider information in respect to the formation of the photographic image. The action of light upon iodide of silver, the existence of an invisible image upon the sensitive plate, the action of the reagents which render the picture visible, all these are problems not yet solved. Notwithstanding the ingenious theories put forward by such men as Monckhoven, Poitevin, Davanne, Vogel, Carey Lea, and others, the phenomena are still unexplained. It is for this reason, on account of this black screen placed against the horizon of photography, and completely shut ting out the view beyond, that no formula for a collodion can be recommended as practically and theoretically good. The mathematician, by calculating the details of his work, is able to obtain a very correct idea of the total, as the partial inaccuracies on one side or the other mutually destroy one another. The mixture of the three collodions is based upon this principle, and it gives, we repeat, the best results. ON THE SENSITIVENESS OF PHOTOGRAPHIC PREPARATIONS* When the approach of autumn warns us that the fine weather and the long, bright days are coming to an end, and that we must prepare ourselves for the dull and feeble light of winter, it is a source of regret to those among us who do not possess an open, unconfined studio, that our pre sent process of negative-taking necessitates so lengthened an exposure. It seems quite superfluous to make any re marks upon the great value of short exposures, and if, on a recent occasion, an English gentleman has stated that he prefers results obtained with long exposures to those taken with shorter periods, on account of the less astonished and less forced expression of countenance exhibited by such portraits, we can only regard such statement in the light of a joke, for, as a matter of course, as soon as an efficient, in stantaneous process has been discovered, no extraordinary skill will then be requisite on the part of the operator to secure any desired facial expression. We believe that it is matter of importance, now that we are enabled, after some experience, to obtain pictures of any description we may wish, whether vigorous or soft, sharp or bold, to turn our attention to this subject, andgto commence researches which shall have for their end the devising of a method for increas ing the sensitiveness of our photographic preparations. Researches in this direction are the more desirable inasmuch as very recently great improvements have been made in pho tographic optics, and we are now in possession of lenses which, in regard to depth of focus, sharpness, &c., are some thing perfectly wonderful, although, unfortunately, a longer exposure is necessary by their employment. One need not be a very great enthusiast in order to pro phesy a warm and eager reception to a thoroughly practical, instantaneous process; every photographer who has essayed children's portraits will admit this. It would then be scarcely necessary for an artist to expose in his studio the usual notice, worded something like the following:— • Cartes-de-visite, ten shillings per dozen. Children pay double." When we remember that the long exposure which was necessary in the early days of photography was considerably shortened, first by the introduction of collodion, and after wards by the employment of iron development, and that during the last ten years very little has been done, except in a slight degree (by more strongly iodising the collodion), to increase the sensitiveness of the negative, although the subject was one that photographers have con tinually hoped to improve, we must admit that our progress * notographisclies Archie.