Volltext Seite (XML)
THE PHOTOGRAPHIC NEWS. Vol. VII. No. 247.—May 29, 1863. CONTENTS. PAGE Recent Modifications in the Tannin Process 253 Scientific Gossip 25± A Plan to make Conservatories available for Photographic Pur- poses 255 Formic Acid in the Developer. By K. Staunton 256 The Diorama and Photography 257 Dry Collodion. M. Liesegang on Mr. Keene’s Process 228 Collodion : Wet or Dry. By M. L’Abbe Despratz 279 On Photography as a Fine Art. By W. D. Clark 259 Photographic Piracy 261 Proceedings of Societies 261 Correspondence—Foreign Science, &c 262 Photographic Notes and Queries 263 Talk in the Studio 263 To Correspondents 264 Photographs Registered during the past Week ............... ......... 264 RECENT MODIFICATIONS IN THE TANNIN PROCESS. The tannin process in its original simplicity rarely fails to give good results where the manipulations are conducted with reasonable care and the materials are moderately near the mark as to purity and exact formula. As modifications are introduced, difficulties begin to be felt, and it has generally happened that these difficulties have borne a somewhat definite ratio to the increase of sensitiveness gained. The more sensitive the flim becomes to light, the greater the tendency to fog and other troubles—such as want of intensity, &c. These conditions are not necessarily con fined to the tannin process, but appertain, in a greater or less degree, to all processes, wet or dry ; and we simply note the circumstance to remark that in proportion as improve ments in sensitiveness arc effected, in such proportion will precision as to formula and care as to the manipulation be come imperatively necessary. The increase in the proportion of bromide, whilst it gives increased sensitiveness and softness, renders necessary more care to secure other conditions of vigour. The use of ammonia in development, whilst it shortens the exposure, demands more care to avoid fog and stains. The use of hot water in development brings about similar results. The addition of honey or gum to the tannin, whilst it has in many, anus increased the sensitiveness, has in others injured the stability or keeping powers of the plates. The latter aids, the use of honey or gum, or the aid of heat in development have proved in Major Russell’s hands, of such doubtful value that he does not adopt or recommend them as integral portions or his process. On the other hand, we may remark that the most suc cessful rapid tannin photographs wo have seen, have been obtained by one or the other of these aids. The best rapid dry-plate picture in the late Exhibition was Col. Stuart Wortley's quasi-instantaneous “ Sun-set at the Island of Ischia.” This was obtained on a large tannin plate with a Dallmeyer's triple lens, highly-bromized collodion, and the aid of heat in development. With the aid of honey and other modifications, Mr. England has obtained some of the best and most rapid tannin negatives we have seen. His experiments are not yet completed, and as there is some probability that he will compete for the Marseilles prize, he does not at present publish his formul ; but we may state that on a recent visit to his studio, we saw a plate exposed which gave a moderately good and very soft nega tive, produced in a very bad light, with about double the exposure which would have been necessary for the wet pro cess. Other negatives we saw which had been produced in a good light, that had all the delicacy and general charac teristics of those obtained on wet plates. Wo are at liberty to mention so much of Mr. England s operations as may be suggestive to other experimentalists. A very large proportion of bromides is used, and in some cases an equal proportion of iodides. In the case of the plate we saw exposed, the collodion had six grains of iodide and six grains of bromide to the ounce. The plates were well washed and the preservative contained both tannin and honey, five grains of each in an ounce of water. After exposure, the film was moistened with common water; a solution of carbonate of ammonia, a grain and a half to the ounce of water was then applied, which brought out a phantom image. Next a mixture of this solution with a little pyrogallic acid was used, by which the image was fully developed ; but without vigour. It was now intensified with pyro and silver in the usual way. The whole operation of development did not occupy more than four or five minutes, was effected without any fog, giving an image very like that of a wet plate, and although the glass had no preparation except grinding the edge, there was not the slightest tendency to loosening of the film manifest. We have since printed the negative and although it looks unusually thin for a dry plate it prints well. Major Russell who has been indefatigable in establishing the conditions of success in working his process, has recently in answer to the queries of one of our correspondents, furnished us with copious and interesting details as the probable sources of certain difficulties to be met. And as the difficulties of one experimentalist are probably those of many, we shall give here a condensation of those of the corre spondent in question, and then add the information with which Major Russell has so kindly favoured us. Our Correspondent, who signs himself “ Tyro Tannin,” says:— I made my collodion exactly as in Major Russell’s formula. The plates were coated with a rather strong solution of gelatine put on warm. The bath was sixty grains to the ounce, satu rated with bromide of potassium, and slightly acid with nitric acid (is this right ?). The developer, six grains, carbonate am monia, one grain pyrogallic acid to the ounce. In the first place, I found the film tender in the bath, and easily torn or peeled off, and when it got through the washing entire on de velopment, in all cases rose into blisters. In one or two instances I have been able to get the picture to the proper intensity without fogging,but it has almost always fogged over when about half-finished, although I did not keep the developer long in and it always remained quite clear. On trying to finish the development, with the ordinary pyro-acetic acid and silver, having washed off the carbonate of ammonia, I found that the blisters caused spots. I have tried a few plates, from which the following appear to bo the results of different ways of developing : That newly mixed or old mixed developer, six grains am monia, one grain pyro, are equally good, and both fog the picture before completion. That development in a tray of the solution has no advantages in that respect. That an advantage seems to be gained by covering the plate first with a very strong solution of carbonate of ammonia , which starts the development, and on adding a few drops of a solution of pyro gallic acid, one grain to the ounce, the development proceeds rapidly. The process appears to be extremely good as to sensi tiveness. I tried a plate with part ten seconds, and other i parts twenty, thirty, and forty seconds respectively. In the ten
