Gelatin Silver Bromide emulsion is na ordinary emulsion sensitive to UV, violet, blue and blue / green, of a sensitivity evaluated aproximatly to 1 ISO.
As this emulsion is not sensitive to all the colors of the visible spectrum, the evaluation of the parameters of the shooting will have to be tamed. Indeed, these will vary according to the color temperature of the lighting and the tone of the subject itself.
You will see that there is really nothing complicated to make the emulsion if you stay clean and careful (is much easier to put into practice than collodion).
They are developed under red safe light, by inspection, which is a great advantage.
The gelatin silver bromide emulsion is extensively explained and exemplified on the Disactis website (Lionel Turban), in its article “Emulsion Noir et Blanc au Gelatino-bromure d'Argent (http://disactis.com/gelatino/gelatino.php) , so the whole description I'm going to make of this technique is the one executed in this article.
Material needed:
2,5gr Silver nitrate
2,0gr Potassium bromide
8,0gr neutral food gelatin sheet (or photographic gelatin)
100gr demineralized Water
Pipette or graduated test tube
Precision scale
Plastic containers
Spoons and plastic knife
Plastic flat bowl
Plastic baguette
Large glass jar with lid
Plastic utensils are recommend because this material is not likely to act with the salts that we use. It is the same for demineralized water.
This is the formula for 120gr of emulsion:
Solution A: I weigh 60gr of demineralized water at room temperature, to which I add 2g of potassium bromide and let the bromide dissolve completely. When the bromide is completely dissolved, I add 8gr of gelatin.I leave this solution A on a corner of the worktop, so that the gelatin is liquid and squeezes.
Solution B: I weigh 40gr of demineralised water, in which I dissolve 2.5gr of Silver nitrate. (Warning, Silver Nitrate is corrosive to the skin! Wear gloves ...)
Now place both solutions in a water bath at a temperature of 40/45 ° C. In this bain-marie, the gelatin ramoly will melt in brominated water. This temperature also has the effect of acting on the speed of the final emulsion. Indeed, the moderate heat increases the general sensitivity.
From now on, ALL operations will take place under RED safety lighting
When both solutions are at temperature, I take with my pipette, a quantity of solution B Silver nitrate and I add this amount slowly and regularly to the brominated solution by actively mixing, adding all of the Solution B in the brominated solution A. (Precipitation). The emulsion has become milky, of perfect whiteness. Once the silver solution has been added to the gelatina halide solution, the sensitivity of a simple bromo-iodide emulsion can also be increased by a process called ripening: the hot emulsion is kept at a constant temperature to promoteb the growth of large silver halide particles that are more sensitive to light than smaller particles.
I pour the hot emulsion into a flat bowl in a sheet of a few millimeters thick, so that it cools and sets into a gelatinous mass and then put your emulsion on the fridge (the faster the setting in mass will be, the better it is for the emulsion). Do not forget to never subject it to any light!
When the emulsion has set, I cut it into small squares using a plastic knife and, under a few millimeters of cold water, I take off the small squares with the blade of the knife. I pour everything into a glass jar with its lid.
It will now be necessary to wash the emulsion. Indeed, the combination of Silver Nitrate with Potassium Bromide produced a precipitation of silver bromide. If our light-sensitive halosel is present, the fact remains that the chemical reaction also naturally produces another salt, Potassium Nitrate, which is useless or even harmful to the emulsion. Fortunately, this salt is solubilized in water, unlike silver bromide. I will be able to eliminate this salt by successive baths of cold water.
The elimination of Potassium Nitrate will be done in 10 successive baths of 30 minutes to 1 hour each. Now it is necessary to drain the water without losing the emulsion.
I recast the emulsion in a water bath at 40°C (digestion)- this is another opportunity for the silver halides to grow by heating the emulsion for a given period of time.
And the emulsion is now ready for use!!!
For a 18x24cm plate size, Lionel Turban take 16ml emulsion,depositing the emulsion on the left side of the plate and when all the quantity is poured, quickly spread the emulsion in the left corners of the plate using a thin plastic rod never leaving the surface of the plate (in the document, all this technique - the most difficult part for me - is well exemplified with photographs).
I use a syringe to spread the emulsion and while I'm depositing the emulsion I go with the syringe itself spreading the same through the glass.
This emulsion can be used for both shooting and printing.
It can adhere to virtually any medium. I have experience of using this emulsion in materials such as paper, cloth, canvas, wood, metal, bitumen wall. In some surfaces, it is necessary to make previous treatment with gelatin or varnish. I present in my gallery of "other materials" some of the work made by me.
After having emulsified the materials, It must now be allowed to mass and dry in the dark, especially in the shelter of dust.
According to Lionel Turban, some of the commercial developers may damage the image obtained with this homemade emulsion, for which I use the developer also made by him:
1l water + 2gr genol (developer- detail) +35 gr sulfite sodium (preservative) + 5gr hydroquinone (developer, contrast) + 25gr potassium carbonate (reaction accelerator) + 1gr potassium bromide (anti-fog).
Use 1+1. Development for 3 to 10 minutes (visual control of the development).
(I also have good results with the Kodak D49-like homemade developer:
500ml water at 50º + 3gr metol + 45gr sodium sulphite + 11gr hydroquinone + 45gr sodium carbonate + 2gr potassium bromide
+ water up to 1 liter)
As fixer, I use my homemade fixer:250gr sodium thiosulphate + 600mL water 50ºC + 2drops acetic acid 28%
(we can add sodium sulfite - reaction accelerator - and sodium metabisulfite (preserves the fixer)
Important sites:
http://disactis.com/gelatino/gelatino.php Disactis - Emulsion Noir et Blanc au Gelatino-bromure d'Argent.
http://thelightfarm.com/Map/DryPlate/Osterman/DryPlatePart4.htm Mark Osterman's Dry Plate Emulsion Recipe
https://www.timlaytonfineart.com/making-simple-silver-gelatin-emulsion-osterman.pdf Making, Coating and Processing a Simple Gelatin Emulsion Mark Osterman, (This piece was written as a chapter for The Book of Alternative Processes, 2nd Edition, Christopher James, 2008)
For those who wish to do a more in-depth study:
My album "dry Plate" on Flickr:
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