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The photographic news
- Bandzählung
- 12.1868
- Erscheinungsdatum
- 1868
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 502, April 17, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
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- Register The Index To Volume XII 619
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Band 12.1868
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190 THE PHOTOGRAPHIC NEWS. [April 17, 1868. had had-the pleasure of examining the great book opened in Paris last year—he meant the International Exhibition—in company of four of the master minds of this country, of which Sir Charles Wheatstone was one, and they were painfully strack with the inferiority of this country in the arts of design : with manufactures which might enable us to clothe the world, we had yet much to learn in this respect. He hailed, therefore, with great delight every agency which should advance us in this respect, and enable England to maintain its position in the progress of art and industry, and preserve its superiority in our time, as it had in bygone ages. In answer to a member as to what were the essential features in this process differing from that of Sir Henry James, Mr. GEIGGS said that the essential point was the fact that he washed away the superfluous matter from the transfer with cold water, and Sir Henry James with hot water. By doing this Sir Henry James removed all the gelatine as well as the ink from the lights ; whereas he (Mr. Griggs) only removed the ink, leaving the gelatine, which gave him an advantage in transferring, the gelatine causing the print to adhere to the stone, without risk of moving, when passing two or three times through the press in transferring. His paper also received a preliminary coating of starch. In answer to Mr. Mayall, he thought that there would be no difficulty in transferring impressions on to a cylindrical rollers. Mr. Peter lb Neve Foster, in answer to some remarks, said that the essential distinction between the transfer of Mr. Griggs and Col. Sir Henry James was, that the latter removed everything, both ink and gelatine, from the transfer, and Mr. Griggs removed the ink only, leaving the gelatine in the lights. Mr. Mayall thought Sir Henry James’ process was excellent for maps, but it struck him as scarcely equal to Mr. Griggs’ for artistic purposes, the latter having more delicacy. Mr. Griggs did not wish to make claims to superiority, but his aim in leaving the gelatine was to support the fine lines, as when they were left in relief and all gelatine removed, they were apt to break down under the pressure of transferring. The Chairman, in a vote of very hearty thanks to Mr. Griggs for his interesting and practical paper, said that every one was indebted to Sir Henry James for having so early published his process in a blue book, and so prevented it being locked by a patent, which it would otherwise have been. The process of printing in various colours was, in his own estimation, of peculiar interest, on account of the nicety and mathe matical accuracy necessary in securing the register of the prints produced from such a number of stones. He felt sure they would heartily thank Mr. Griggs for his paper and for the valuable practical demonstrations. The thanks were expressed by acclamation, and were duly acknowledged by Mr. Griggs. The Chairman then read the following letter on the subject of Mr. McLachlan’s discovery :— “ Dr. Hugh Diamond, Honorary Secretary of the Photographic Society. “ Sir,—We have the honour to report that on the 12th February last we met Mr. McLachlan by appointment at the rooms of the Society of Arts, and that he then explained to us the principles of a scheme of photographic practice by which he claims to have excluded many difficulties and sources of failure in the production of collodion negatives. Mr. McLachlan attaches great importance to the selection of particular qualities of certain photographic chemicals, samples of which have not, however, been submitted to us. “ Without such aid to guide us, experiments were conducted at Woolwich with the ordinary materials, and we succeeded in realizing some of the conditions promised by Mr. McLachlan. “ The question as to how far the permanence of the bath and uniform working of the collodion and other chemicals may be guaranteed according to this plan must be left for future ex periment to decide.—We are, sir, yours &c., “ P. Le Neve Foster, M.A. “ London, April 8th, 1868. “ John Spiller, F.C.S.” The Chairman then said that Mr. McLachlan had come from Manchester that day purposely to communicate to the members of the Society his valuable discovery, but it was un fortunately too late to go fully into it. He would ask him to give them briefly some information as a preparation for the paper he promised to read next month giving fuller information. Mr. McLachlan said that as what he had to communicate was the result of almost a lifetime of experience to which almost everything else had been sacrificed, he could only very partially enter into the subject in the short time then possible. He had been led to examine the subject from his ex perience, which resembled that of all photographers, namely, that things would work well for a week, and then, for a week or two more, almost everything would go wrong. As they were using the same things it was clearly a question of condition of the chemicals, which, if kept in a proper state, ought to guarantee immunity from all failures except those of manipulation. After briefly stating the common practice in photography, and its uncertainties and troubles, he said his aim had been, then, to prepare his bath and his collodion so that pure iodide of silver would bo formed in the film in equivalent proportions, without the disturbing influence of acid, which tended to separate the iodide from its base. He had suc ceeded in preparing a bath without acid, which could not be charged in excess with the fatal source of pinholes—iodide of silver—which, while holding oxide of silver in solution, would not fog the plate. Then he prepared collodion to suit the bath, and for convenience he modified commercial samples. As usually sold, all collodions were made from cotton prepared with an excess of sulphuricacid: they contained an acid, not sulphuric acid, but something analogous to it; this caused streaks, brain markings, &c. It was held by photographers generally that nitrate of silver was not altered by light. Now he found it was altered, and this was an important element in his conclusions. His method was as follows:—He took crystallized nitrate of silver, not the recrystallized. By preference ho used a black- looking sample, which was generally rejected ; it seemed moist and dirty, and appeared to contain a good deal of the water of crystallization. Members could best judge of what he meant by examining the sample he now exhibited. With this ho made a bath, at the rate of one ounce to one ounce of pure distilled water. Taking six ounces of solution so prepared, and putting it out in a 40-ounce bottle to the action of light, he left it as long as he could. Ho preferred three months of the warmest and sunniest portion of the year; but one month, or even less, would do a good deal. If the water and silver were pure and neutral, no apparent change would take place ; if the solution were made either acid or alkaline, the effect of light was con siderably limited. Now, to test the change effected, he made a solution of caustic potash, 1 grain to an ounce of distilled water. If a drop of this were added to an ounce of the silver solution before it were sunned, a turbidity would be caused by the pre cipitation of oxide of silver ; but after the sunning, on adding the potash solution, the bath would have been found to have acquired the property of holding oxide of silver in solution; and although a considerable quantity might be formed, it was re- dissolved, and the solution remained clear after shaking up a little. Practically, he only added 1 drop of potash solution to 1 ounce of silver solution, so as just to secure a slightly alkaline condition. He then took 2 grains of iodide of potassium and dissolved in a very small quantity of water, say 10 minims; this he added to 10 or 12 minims of the strong silver solution, which was then diluted to the strength of 35 grains to the ounce, and, singularly enough, no precipitate of iodide of silver was formed on dilution, nor would any indication of the presence of excess of iodide of silver be present on working. After the lapse of a few days, however, a curious change took place : the iodide of silver was all precipitated suddenly, ami after that, no matter how much water was added to dilute the bath, no turbidity or apparent presence of iodide of silver was produced. This was the bath in perfect working order, slightly alkaline. He next prepared a suitable collodion ; and, for simplicity, he would mention one excellent sample of commercial collodion—he referred to Mawson’s. He would take this in a ripe, red, acid condition. If used in the bath as prepared, it would give brain-markings and stains, because ot the antagonism of conditions. It must bo made to harmonize with the bath. He therefore took the potash solution and added about 4 drops to a 5-ounce bottle of collodion; this neutralized the acid, making the collodion nearly colourloss ; and this neutral collodion employed in this alkaline bath would give clean brilliant negatives without a trace of fog, at once delicate and vigorous. Ho required, however, for the best result, a suitable developer. For this he preferred the common dark green dirty-looking protosulphate of iron. But as it was often more difficult to get this than the clean, pure, light green crystals, ho would describe his mode of making the developer with the pure sulphate. He took 16 ounces of a 12-gra1
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