The photographic news

• Bandzählung: 27.1883
• Erscheinungsdatum: 1883
• 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-id1780948042-188300004
• PURL: http://digital.slub-dresden.de/id1780948042-18830000
• OAI: oai:de:slub-dresden:db:id-1780948042-18830000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

APRIL 6, 1883. ] THE PHOTOGRAPHIC NEWS. 221 ON GELATINO-CHLORIDE EMULSION IN THE CAMERA. BY ALEXANDER COWAN.* The only apology I can offer in bringing before you this evening, the subject of gelatino-chloride emulsion is the fact that, whilst on all hands the beauty of the process is acknowledged, yet there somehow exists the idea that it is of necessity a slow process, and only useful for contact-printing from negatives of the same size as the positive required, and is not available for artificial light or for reduction in the camera. That this opinion does exist, and has often been expressed, I know ; and in proof of this I should like, for a moment, to quote a paragraph from an article in the British Journal of 23rd February last, in which the Writer says:— “ Where negatives are specially taken of the required size, and when contact-printing consequently is possible, nothing can exceed the beauty of the results producible by means of collodio- bromide, carbon, Woodbury, or gelatino-chloride, with ferrous- citrate or citro-ferrous-oxalate development; but unfortunately these methods are too slow, as a rule, for employment in the camera when reduction is necessary, so that the wet-collodion process continues to be used by the majority of makers of lantern slides.” Again, a little further on, the writer of the article, after remarking on the beautiful tones that the gelatino- chloride plates are capable of producing, says: “ However, as I have said, gelatino-chloride is too slow for camera work, at least for the majority of amateurs.” Every one who visited the exhibition at the Society of Arts was struck with the beauty of the transparencies by the gelatino-chloride process exhibited by Dr. Eder, and the sight of them no doubt induced many besides myself to try the process. I believe the article, as published by him in the Year-Book of Photography for 1882, contains all the information required for any one at all conversant with emulsion-making. For convenience, however, I will give the exact formula and mode of working in English weights and measures, and I should like to add at this time that I can tell you nothing original, but all that I can tell you has been begged or borrowed from every available source at command. The proportions for emulsions such as these pictures have been printed on are the following :— Silver nitrate ... ... ... ... 950 grains Sodium chloride 480 „ Gelatine (Heinrich’s) 960 „ Distilled water ... ... ... 30 ounces The silver is dissolved in 10 ounces of the water ; the chloride and half of the gelatine in 15 ounces, and the other half of the gelatine in the remaining 5 ounces of water, after having been allowed to swell for some time previously. All the vessels are heated to about 120°, or sufficiently to thoroughly melt the gelatine, and are then removed to the dark room, and the silver solution mixed with the gelatine, and then slowly emulsified into the gelatine and chloride ; this is then poured out into a flat dish and cooled rapidly with running water, and, when tho- roughly set, washed in the usual manner. This makes from 40 to 50 ounces of an exceedingly fine emulsion, and very slow —just the thing for making transparencies by contact-printing and development by ferrous citrate or ferrous citro-oxalate, but for camera work is certainly, under ordinary circumstances, too slow. I will now hand round some slides taken in the camera, and give the formula used to make the emulsion. I should like to say, before doing so, that, as far as I have experimented, I have not tried to obtain the extremely warm tones on plates exposed in the camera, for reasons which 1 will explain further on. For the emulsion for quick plates the same proportions are taken, with the addition of 40 minims of a 10 per cent, solution of hydro chloric acid; but only one-quarter the bulk of gelatine is used ; half of this is mixed with the chloride, and half with the gela tine as before, and the remaining three-fourths left to swell in water. As soon as the silver and chloride are emulsified together, the vessel is removed to the boiling arrangement and boiled for fifteen to thirty minutes or longer, according to the rapidity required, and then the remainder of the swelled gelatine at once stirred in, a leaf at a time, put by to set, and washed in the usual way. The developers used in the experiments I am about to detail were—the ordinary ferrous oxalate; the ferrous citro- oxalate of Captain Abney ; the ferrous citrate of Dr. Eder. • Read before the Photographic Society of Great Britain. The first plate I hand round is printed out direct on citro- chloride after Captain Abney’s formula; but as I have as yet had so little experience with it, I have no remarks to make. The other two contain a series of transparencies printed in contact by gaslight, and developed by {various modifications of the developers I have mentioned ;. and as they are all numbered, I can give any information respecting any one of them if required ; but as I propose to show you some others of which I have noted more exactly the conditions observed in each case, I will pass them on without any further comment. The two slides of group are the first trials I ever made in the camera, and were exposed to reflected light from a bright sky for forty- five seconds ; and one developed with ferrous citrate without any restrainer, and the other with the addition of a trace of ferrous oxalate. The next series are printed by gaslight on slow plates, and will be explained by those that follow. I have not found, when using the ferro-citrate-oxalate developer, that the length of exposure has any effect on the colour of the image, and I think the following experiments will illustrate this:—Six plates were exposed to the same light, viz., three inches from a gas flame, each plate having one-half more expo sure than the other, the first having forty seconds, and the last 303 seconds ; and I think you will see that there is no difference in tone, but only an increasing depth of the same colour ; the whole of them are developed for the same length of time, viz., thirty seconds. The first of the series of comparative experiments I propose to show you contains six exposures made in the camera on a very dull day, with varying exposures from five to ten minutes, and developed as the last, with varying proportions of the same developers; but the remarks I have to offer further on will explain any differences that may be noticed in them. With ferrous-citro-development I have been able to get a variety of tones, as the examples handed round will show ; the majority of these plates have been exposed to artificial light, as being more constant when experiments have to be taken up at any leisure moment. The first plate was exposed for sixty seconds, 3 inches off gas flame, and developed with ferrous citrate (made with liq. ammonia) for ten minutes. The next plate treated exactly the same; but the developer was made with carbonate of ammonia, and gives an image of double the density. The next plate had only half the exposure, and was treated the same, and still gives a denser picture than No. 1, thus proving to my mind that the developer made with the carbonate is much more powerful than that made with liq. ammonia; so for all subsequent experiments I have used the carbonate. In the next plate, No. 4, I gave eight times the exposure of the last, and developed for only one quarter the time (24 minutes), to see what effect long exposure had on the colour of the image, and to my mind it conclusively proves that great al teration in colour is not to be gained by great differences in exposure when using a constant developer ; but I think that the further examples will show that, with very prolonged exposures and same developer powerfully restrained, a great variety of tones may be produced. The next plate, No. 5, will, I think, explain this, as it was treated in all respects the same as the last, but with the addition of one grain of chloride of sodium added to each ounce of the developer; this plate took forty minutes to develop, but you will notice a very distinct change of colour. In the last plate on this series, only half-a-grain of restrainer was used, and only fourteen minutes’ time of develop ment, and I think these last two examples show the great re straining power of the chloride. In the next series I determined to test this point more tho roughly, and, as the exposures to gas-light would be tedious, I made the next six plates by daylight, giving the first one five seconds, and using two grains of chloride as restrainer, and deve loping ten minutes; this, although a great over-exposure for an unrestrained developer, was not enough, so the second plate was given twenty seconds to daylight, and developed the same time, and proved about the right exposure, although, from the experi ence gained by the previous series, the exposure was twenty times more than would be required by the same developer with out any restraining chloride; but the colour of the image is totally different. In the next plate, No. 3, I again doubled the exposure, giving forty seconds, and doubled the chloride, using four grains to each ounce of developer, and developed for same time—ten minutes—the result being a distinct change in colour. Up to this stage I should say that I had entirely used slow plates ; but