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Processes - Gelatino-Bromide Emulsions

Gelatino-Bromide Emulsions 1875 - ... Discovery Earlier Processes From the 1850s until the mid-1870s photographers used glass plates coated with collodion, the collodion being wet or dry. Then experiments began, making the emulsion coating with gelatin, so creating gelatino-bromide emulsion plates. Gelatine had the advantage of being fluid when warm and a jelly when cold. Pioneers in the 1870s Pioneers of the gelatino-bromide process were Mr King, Mr Burgess and Mr Kennett who devised and patented a method of drying the gelatin to form a pellicle, that then needed only to be dissolved in water to be ready for use. WJ Gough experimented with the process and claimed to obtain greater density in his negatives by including a chloride as well as a bromide in his emulsion, but encountered some difficulties with fogging. [Article: Gelatino Bromide Emulsion by JW Gough in BJP: 8 Jan 1875; p.15] Accepted by the 1880s By the 188s, the Gelatine process had become well established. The ABC of Modern Photography, published in 1884 said: "We shall give instructions in printing, so as to enable the student to complete his picture. In fact our desire is to produce a manual of photography for beginners, on the assumption that the gelatine process is now the photographic process of the day." [ABC: Page 4] Process Advantages of the Gelatino-bromide Process Rev. AH Palmer spoke highly of the gelatino-bromide process in his communication to Edinburgh Photographic Society, written following his lecture to the society in January 1876. He described the process as reliable, simple, inexpensive and had the advantage of producing no fumes of ether. In this communication, he explained the processes he used. Others described their processes in the British Journal of Photography in the mid-1870s. Below is an account in 1875 from a contributor describing himself as 'Amateur'. To make 1 ounce of emulsion ... 1. Soak 15 grains of Nelson's patent opaque gelatin in a 2 ounce bottle of water for several hours. 2. Pour off the water and add 2 drachms of distilled water and 18 grains of bromide of potassium. 3. Place the bottle in hot water until the contents are dissolved While doing this ... 4. Dissolve 25 grains of nitrate of silver in 2 drachms of distilled water. Then take all into the darkroom, and ... 5. Add the silver to the bromised gelatine gradually, shaking well between each addition. 6. Add 1 or 2 drachms of methylated spirit. 7. Add sufficient water to make up the quantity to 1 ounce. Allow it to rest until the next day 8. Dialyse for 4 or 5 hours (following Mr King's directions) To coat the plate ... The plates should be coated as soon as possible (though in cold weather, the emulsion may keep good for 2 weeks). 1. Clean the plates well, particularly at the edges. 2. Guide the emulsion over the plates with a glass rod. 3. Place the plates on a level dry shelf to dry, covered by a board about 1 inch above, to protect them from falling dust. The plates should have dried by the next day, and "present a beautiful glossy and transparent appearance like opal glass. Develop, Fix, Intensify After exposing the plates they should be laid in a tray of water for a minute or two to soften the film. 1. Develop in a strong alkaline developer alone. 2. Fix the plate. Washing details before and after fixing are not given, except as below. If the plate needs to be intensified 3. Immerse the plate in a solution of bichromate of mercury until the picture appears distinctly as a positive by reflected light. 4. Wash 5. Apply ordinary alkaline developer without the bromide. Any shade from rich brown to jet black may be obtained. Modified methods 'Amateur' claimed to have tried almost every modification that he could think of, including the addition of an iodide and a chloride and an excess of silver with aqua regia, added both before and after dialysing the emulsion. However he found the plain bromised method, described above, to be simpler, more certain and as sensitive as any. Kennett's Pellicle method 'Amateur' claimed that Kennett's Pellicle emulsion method was more sensitive, but he had never been able to obtain proper density it, and found that it produced results that looked cold and more opaque. He added that if the emulsion described above could be obtained in pellicle form, "collodion might retire from the field". Using Kennett's Pellicle method avoids the need to follow steps 1 to 7 above. Instead the grains of the pellicle are dissolved in water, as was described by HP Palmer in his 1876 communication to Edinburgh Photographic Society. [BJP: 24 Sep 1875; p.462] HJ Palmer's Methods Further comments on the gelatino-bromide process, including advice on the safelight to be used can be found in Palmer's communication to EPS. [BJP: 20 Mar 1876; p.113] Result Short exposures are Possible One of the advantages claimed for the gelatino-bromide process was that it allowed significantly shorter exposure than war required for collodion dry plates. Rev. AH Palmer reported that on a bright January day he had exposed six plates for times ranging from 10 seconds to two minutes, using a Dallmeyer medium-angle rectilinear lens at the smallest of its five stops. The plate exposed for 30 seconds he described as 'perfection'.



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