> > Hello all,=0A=0AI've been experimenting with various alternative formulas f= > or black and white developing that involve non-toxic household chemistry bu= > t I am curious if anyone has done so for color film?=A0 =0A=0A=0AAlso, why = > and how do onions work as a fixer?=A0 How do you prepare them to do so?
Okay, B&W process is easy. Single layer of emulsion, it's got silver halide compounds in it. Light strikes them, knocks electrons off, they get charged. You put it in a developing agent which converts the exposed crystals to metallic silver. Then you put it in a fixing agent which removes all the free halides. There are millions of developing agents out there, and a lot of them are mentioned in Mees' "Theory of the Photographic Process." There are several different ways that they work. Most of them like to work in alkali solutions, some (like pyro) like acid solutions. Among the things that kind of work for development are coffee. Since catechin is a weak developer, a strong cup of tea might also work. You can look through Mees and see some of the various possibilities. For fixing, just about any reducing agent will kind of work. Thiosulfate is nice because it combines the all the various halide compounds rapidly and well and the end products are very soluble. Sodium cyanide works even better, but it's nasty stuff. My inclination is not to try using anything but standard thiosulfate fixers unless you really know what the end products of the reaction are and how soluble they are. I know onion and table salt seem to work, but you can't necessarily know what they're leaving behind in the emulsion and you won't know what they have left for a decade or two, possibly. And no, the Kodak Hypo-Check kit is basically a test for residual thiosulfate ions in the emulsion, it won't detect whatever is left over from onion fixing. > I know an extreme salt solution (extreme as in you put in so much salt the = > water can't take it anymore) will work too but it takes a long time (2 days= > I heard). How long do onions take? Same as with any other fixer.... twice as long as it takes for the film to clear. The one time I tried it, it was all afternoon. >=A0 Isn't the real danger from fixer the= > metallic silver that needs to be properly disposed of? Yes. Except that it does not need to be disposed of, it needs to be sold because silver is increasingly worth money. Don't waste it, ask your local print shop who does hypo disposal for them! >=0A=0AFinally, has a= > nyone come up with a good substitute for r-9 or r-10 bleach in the bw rever= > sal process.=0A=0AThanks=0AKathryn=0A=0A=0A=0A_____________________________= The reversal bleach needs to be something that will dissolve metallic silver without affecting the unexposed halides. R-9 is the traditional sodium ferricyanide bleach, it works very well and it's not really all that toxic unless it is combined with an acid. R-10 is a mix of potassium permanganate and sulfuric acid that produces potassium persulfate in solution which is what does the actual job. I don't know of any easy natural sources for any ferricyanide or persulfate compounds, but I know that sodium ferricyanide was known in the 18th century and is used in making prussian blue dye. My suspicion is that to do a proper bleaching job you will need something from one of those two chemical families. ANYWAY.... to answer your original question, Kodak process color films all have most of the complicated stuff built into the film, not into the processing. There are three individual layers of B&W emulsions, each sensitized for a given range of light colors, and each with a dye material in the emulsion itself. (Yes, I am oversimplifying this in the case of the yellow layer but I've already gone on too long). The first step is a conventional developer that generates a conventional silver B&W image on each of those layers. You can use whatever developer you want, including coffee or Acufine or whatever gives you the look you want. The second step is where all the fancy stuff goes. The color developing agent connects those dyes up to the metallic silver in each of those emulsions and since the dyes are in the layers when the film is made, each layer gets connected to dye of the proper color. This is the fancy stuff, and there is no substitute for the color developing agents. I believe they can both be ordered in small quantities from Photographer's Formulary. If you try and order CD-3 from Kodak their minimum order is a barrel. Then it's just a matter (for negative film) of washing out the unneeded dyes, bleaching out the silver image, and cleaning up any residual undeveloped halides. You can, in fact, leave out the bleach step and leave the silver image and the color image behind together, which gets you a more contrasty image with less saturation. This used to be a standard trick for press photographers working in low light. Aside from the color developing agent and the bleaching, the color process is very much the same as the B&W process. This whole thing is ingenious as hell especially when you compare it with Kodachrome or Agfachrome. --scott _______________________________________________ FrameWorks mailing list [email protected] https://mailman-mail5.webfaction.com/listinfo/frameworks
