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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
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- SLUB Dresden
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- Public Domain Mark 1.0
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- urn:nbn:de:bsz:14-db-id1780948042-186800009
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- http://digital.slub-dresden.de/id1780948042-18680000
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- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 500, April 3, 1868
- Digitalisat
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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
Band 12.1868
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- Titel
- The photographic news
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HE PHOTOGRAPHC NEWS. April 3, 1868.] 165 importance, as in most dry processes. Common negative cotton is not suitable, but a powdery pyroxyline of the intense sort is necessary. That sold as “ Helion No. 1 ” gives very good results. It is curious that the intense pyroxylines which give the least sensibility with wet plates give the greatest with the dry. Of course, the collodion will be better after standing a while. To obtain a smooth plate with collodio-bromide requires more care than with plain collodion. Pour on plenty, commencing far up the plate. Get it quickly to the upper corners, and then bring it down as squarely as possible ; avoid the necessity, as far as practicable, of bringing it down first on one side and then on the other, and get it down as straightly as possible. To do this the supply must be abundant. Pouring off requires especial care, or else an uneven band will be formed across the upper end of the plate. To avoid this, raise the further end of the plate in pouring off very slowly and regularly ; give the plate a wide, slow, rocking motion. Attention to this will be found important. I should have said that the plate, before collodionizing, must have an edging of india-rubber dissolved in benzole. The variation upon this process consists simply in wash ing the plate after collodionizing, and before plunging it into the bath. This makes a great difference in the plate. Treated in this way, and with a moderate exposure, clear, bright negatives are got, resembling very closely those afforded by wet plates, and showing as positives by reflected light. The deeper shadows are represented by clear glass ; there is a complete absence of veiling, and brilliant pic tures are easily got; but the great sensitiveness of the plate is materially diminished, the exposure is prolonged (must be from one-half more to double), and the details in the shadows are not so well preserved. I prefer, therefore, as a general thing, the first-described system, in which the plates are plunged into the lead bath as soon as set, and without preliminary washing. And I would call attention to the fact that, so far as I am aware, no one has previously pro posed any method in which plates prepared in any other way, either with collodio-bromide or in any other form of the collodion process, can be sensitized without a previous washing. This new mode of operating has the double advantage of saving time and trouble, and giving a better result. It seems especially applicable for the preparation of dry plates in travelling, as the two greatest difficulties are done away with—the nitrate bath and the washing—for water with which to wash the plates made on a journey is apt to be scarce in quantity and of extremely doubtful quality. Another MODIFICATTON. An interesting modification of this process is one in which the lead and gallic acid are introduced into the collodion. For this purpose, add powdered acetate of lead to acetic acid in as large quantity as it will take up. Add 5 drops of this and 15 of a 60-grain alcoholic solution of gallic acid in alcohol to each ounce of collodion, using for this purpose the same collodion as above described, likewise sensitized with 10 grains of nitrate of silver to the ounce ; after stand ing, decant the clear portion into a measuring-glass, and add, first the lead solution, stirring well up ; and then the gallic acid. Collodionize, using the same precautions as before described. These plates, after collodionizing and setting, will simply need washing for about five minutes under the tap, and are ready for use as soon as dry. The negatives obtained re semble in all respects those obtained by that modification of the previous described process in which no washing is Hsed. They are very sensitive, and give soft pictures. All these plates are intended for alkaline development, respect- 'ng the proper application of which a few words should be said. Alkaline Development. The form of alkaline development which I have found most suited to those plates is as follows:— 1. Carbonate of ammonia in 20-grain solution. 2. Pyrogallic acid, 300 grains dissolved in 5 ounces of alcohol. 3. Bromide of potassium, 2 drachms in 5 ounces of water. I prefer to develop in pans, and take :— Water ... ... ... ... 6 ounces No. 1 4 ounce Nos. 2 and 3, each... ... ... ± drachm This quantity, placed in a 7 by 9 porcelain pan, conveni ently develops a 6} by 8} plate. The plate, after previous wetting, is left to itself in the solution for about half an hour. The dose of carbonate of ammonia is then trebled,, and intensity soon comes ; if it does not, the plate is left in. until it does. I do not recommend washing off and using silver and pyro, but finishing entirely with the alkaline; treatment. Management of Collodion. It is better, after adding the silver, to shake violently,, and repeat this once or twice in an hour or two, then let repose for twelve to twenty-four hours. In this way no filtering is necessary. After finishing a set of plates, add to the residue of the collodio-bromide I, 2, 3 or more ounces of the bromized’ collodion, enough to more than saturate all the excess of' silver (half as much fresh as what remains is plenty ; more- will do no harm) ; mark the quantity on the bottle, so that, in adding the next lot of nitrate of silver, it may be taken into account. Thus the operator may go on indefinitely, as Mr. Mawdsley has pointed out. It must be well understood that even after this addition, the collodion, though less sensitive, is still very much so, and must be carefully preserved from light, and should be kept in a cool place. Self-Developing Plates. I published lately a description of a method of pieparing plates which would spontaneously develop themselves in the dark slide, given rather as a matter of curiosity, however, than of decided utility. Continuing, from time to time,, my experiments with it, I obtained very irregular results,, especially in respect of fogging. By continued investiga tion, however, I have succeeded in ascertaining the sources; of these irregularities, and in getting rid of most of them. Of the fogging, which was the most serious trouble, I got rid entirely. I give here the results which I found. 1. A picture which will develop itself entirely and not need redevelopment will require a strong, bright camera- image, such as is only got with short-focus lenses and with large diaphragms. The exposure must be as long as for a common tannin plate. 2. But, with shorter exposure, a visible image can be got, which redevelops easily to any strength desired. 3 The images lose, to an unusual extent, in the fixing;, and therefore allowance must be made for it, or else the pictures will need to be returned to the developing bath for a few moments after fixing and washing. 4. Owing to the glycerine used, care must' be exercised) to rock the plate, though, thoroughly, otherwise crapy lines; will result. 5. The same cause, the glycerine in the collodion, dimin ishes the adhesion of the films to the glass, causing them to slip. This is avoided by using a substratum of albumen,, by the aid of which the plates will bear rough handling and rough washing with impunity. 6. Fogging.—This trouble showed itself in a very per plexing way. Sometimes films prepared with a large (com parative) excess of nitrate of silver showed no trace of fogging, whilst at others this result was precisely reversed. It was finally ascertained that the fogging depended wholly upon the condition of the collodion ; after fixing these con ditions with certainty, no difficulty was found in preparing films so entirely free from all tendency to fog that the plates,, after removing from the slide, could be left in plate-boxes for weeks without undergoing any change.
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