Silver Gelatin Emulsion
Basic Recipe: Unwashed Emulsion
This is an extremely simple but highly effective recipe. It produces a very slow emulsion (<~ISO 4 - 12). It works well for contact printing, or use in a camera in FULL sun -- it seems to have a sensitivity rather like Kodak 7363, or HiCon, which I shoot outside all the time. The usual advice about using slow films applies: if you want to use it in a camera, bear in mind that it seems to work optimally in sunlight, and the equivalent amount of tungsten light probably won't work. We haven't tried it with HMI lights or fancy fluorescent lights; let us know if you try it! You might also need to undercrank. To make a faster emulsion takes more work. For that, have a look at our research site ; making a faster emulsion is one of the questions we're trying to answer. For a slow film, however, it works well, so well, in fact, that it doesn't seem necessary to make anything more complex.
For everything that follows, use distilled water, and rinse all implements with distilled water before use. Cleanliness is essential!
Mix seperately (in normal room light):
|Gelatin (Knox brand (or equivalent) plain, unflavored food gelatin, from the grocery store||10g|
|Add the gelatin to the water and allow to swell. Put the container (preferably stainless steel, like a 2-reel still film developing tank) into a water bath and raise the temperature to 50°C. Add the potassium bromide and stir or swirll continuously until both ingredients are dissolved.|
|Dissolve the silver nitrate in the water by stirring or swirling, again, in a stainless steel container (a processing can for 35mm still film is ideal), and raise it's temperature to 40°C in a water bath.|
The next steps must be conducted under a red or amber safelight!
Stirring continuously, add solution B to solutionA in small, regular quantities, so that the addition takes 10 minutes to complete -- about 5ml every 30 seconds. Some say that you should filter the finished mixture through cotton or glass wool or a loosely woven cloth like cheese cloth (making sure to thoroughly rinse the filter material with distilled water first), but I stopped doing this because of the extra step and mess, and I don't do any filtering at all at this point.
The emulsion is now finished and ready to use! Store it in a ligh-tight container -- a daylight spool box works well. Make sure to label it so as not to open it accidentally in white light! To use, heat so that the gelatin melts -- 35°C might be a good starting point, but the consistency will depend on the temperature, and so this will be a matter of personal preference. Refigerate it in the meantime.
As to coating,it sticks well to cleared acetate film that retains it's commercially-given gelatin coating, and seems to stick well enough to uncoated acetate, the clear leader you can buy in bulk. This will require some experimentation on your part. Coat on strips of a manageable length -- say, about 4 feet. Dry in total darkness, and be aware that it is light-sensitive film!
Expose generously -- either outside in the sun if you're using it in a camera, or a flashlight seems to work well for contact printing. It will require some testing in either case to figure out what the right exposure should be, but if you keep the development time constant, this will be the only varialble so this won't be hard.
I like to use a very soft brush that picks up a lot of emulsion, and to redip it frequently. Multiple coats are fine, and help build up enough thickness so that the maximum density of the final image is extremely high. You have to beware, though, too much thickness, which can make the film impossible to fix completely. Bear in mind that this is art, not science! If you want regular results, use commercial film and send it to a lab, but don't send hand coated film to a lab!
Develop in a standard developer and fixer. Use cold water for rinses, and make sure no solutions are over 20°C, otherwise the emulsion might come off. Bear in mind that the wet emulsion is very fragile and scratches easily, and that it is susceptible to veiling, running, and reticulation -- all of which make working with hand-made emulsion exciting. You really should use a hypo-clearing agent at the end, as it is a silver image and will degrade if left contaminated with fixer, but the longer it's in any solution, the greater the risk of falling off, so use your own judgement. If you're just using it as an image source from which to print back onto regular film, this isn't an issue.
One developing method might be:
|Developer D-19||20°C||3 minutes|
|any standard acid hardening or non-hardening fixer||~20°C||until all milky areas are gone (or as gone as possible); ~2 minutes?|
|any Hypoclearing agent||20°C||2 minutes, if you dare!|
|final rinse||<20°C||5 minutes, or as long as you're willing to risk it.|
Hang to dry