Donald Qualls
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When my darkroom was last set up, I had processed a few rolls of C-41 film in homebrewed Dignan two-bath C-41 developer, using Kodak Flexicolor bleach/fix and stabilizer; the results were encouraging (I did it this way because "kits" were too expensive for the amount of film I'd process during their storage life, and Flexicolor developer used a starter/replenisher system that depended heavily on high volume processing).
Now it seems it's gotten hard to get even the blix and stabilizer for Flexicolor online, chemistry kit prices seem even higher, and I'm looking at alternatives to finish homebrewing the process, for both C-41/CN-2 negative films and E-6 chromes.
For chromes, I'll need to mix a single-bath color developer, since two-bath depends on dry film to soak up the Bath A -- or else I'll have to dry the film between first dev and color dev (light fogging is one thing, but hanging the film for a couple hours at that stage might result in enough overexposure to go over the peak of the curve and make the halide lose density). That doesn't seem difficult; there are formulae online and I don't recall them requiring any exotic chemicals; CD-4 was readily available last time I checked and it seems Formulary and another chemical provider still have it.
However, the other step is the harder one -- bleaching. Common fixers work fine on color film stocks (I'd likely end up using two-bath fixing with plain hypo, because it's easy and cheap), but one needs to either remove or rehalogenate the silver first, or wind up with a "bleach bypass" look in negatives and extreme overall density in chromes.
"Correct" color process bleaches for C-41 and E-6 use an iron EDTA which is fairly hard to come by, but there are multiple other methods I know to bleach developed silver: potassium dichromate in sulfuric acid, hydrogen peroxide in citric or acetic acid (or as a two-bath, multi-pass process), potassium ferricyanide with a halogen donor such as potassium bromide, or iodine and potassium iodide. The first two directly remove the developed silver, the latter pair rehalogenate for later or simultaneous fixing. Iodine/potassium iodide is problematic because silver iodide is relatively difficult to fix away, so I don't seriously consider that bleach system. Potassium dichromate is toxic, carcinogenic, and handling the acid is a safety concern (not to mention availability of sulfuric acid in these times).
That leaves two processing I've never attempted (on color film).
Hydrogen peroxide is apparently fairly commonly used to bleach between developers in B&W reversal; with the acid catalyst, it dissolves the silver, which then precipitates in the solution in a form that can redeposit on the film or paper, causing yellow/brown silver staining (which I've seen in video of reversing in-camera paper negatives for direct positive). This can seemingly be avoided by ensuring the emulsion isn't up in the bleach solution. There are other concerns with this process, however: one is that high strength peroxide (9%, 12%, or even 35%, for dilution to working solution) becomes hazardous to handle, and is a feedstock for certain improvised products that might lead to a visit from polite people in dark suits with a bulge under one arm, or very impolite folks with shotguns, battering rams, and body armor. Another is that peroxide is a well known bleach for organic pigments and dyes, and might damage the desired image dyes in color film stocks. I haven't been able to find any reports of anyone attempting to bleach color films with peroxide.
Potassium ferricyanide, either directly mixed with fixer or with a halogen donor, is a long-standing process for B&W; Farmer's Reducer and bleaches for color toning and for sepia/sulfide toning depend on this chemical. Kodak apparently once specifically called it out as an alternative bleach for their own color process (it's been rather a long time, though; this might have been for C-22 films). The primary concern with this process is that I've read that specifically Fuji films may experience a reaction that causes the base or one of the filter layers to turn a strong purple when exposed to ferricyanide bleach. This might be compensated with filtration for negative films, but obviously isn't acceptable for chromes.
And now we come to the question: has anyone here actually use either a ferricyanide or hydrogen peroxide bleach process on color films, to be able to report success, failure, or limitations?
Now it seems it's gotten hard to get even the blix and stabilizer for Flexicolor online, chemistry kit prices seem even higher, and I'm looking at alternatives to finish homebrewing the process, for both C-41/CN-2 negative films and E-6 chromes.
For chromes, I'll need to mix a single-bath color developer, since two-bath depends on dry film to soak up the Bath A -- or else I'll have to dry the film between first dev and color dev (light fogging is one thing, but hanging the film for a couple hours at that stage might result in enough overexposure to go over the peak of the curve and make the halide lose density). That doesn't seem difficult; there are formulae online and I don't recall them requiring any exotic chemicals; CD-4 was readily available last time I checked and it seems Formulary and another chemical provider still have it.
However, the other step is the harder one -- bleaching. Common fixers work fine on color film stocks (I'd likely end up using two-bath fixing with plain hypo, because it's easy and cheap), but one needs to either remove or rehalogenate the silver first, or wind up with a "bleach bypass" look in negatives and extreme overall density in chromes.
"Correct" color process bleaches for C-41 and E-6 use an iron EDTA which is fairly hard to come by, but there are multiple other methods I know to bleach developed silver: potassium dichromate in sulfuric acid, hydrogen peroxide in citric or acetic acid (or as a two-bath, multi-pass process), potassium ferricyanide with a halogen donor such as potassium bromide, or iodine and potassium iodide. The first two directly remove the developed silver, the latter pair rehalogenate for later or simultaneous fixing. Iodine/potassium iodide is problematic because silver iodide is relatively difficult to fix away, so I don't seriously consider that bleach system. Potassium dichromate is toxic, carcinogenic, and handling the acid is a safety concern (not to mention availability of sulfuric acid in these times).
That leaves two processing I've never attempted (on color film).
Hydrogen peroxide is apparently fairly commonly used to bleach between developers in B&W reversal; with the acid catalyst, it dissolves the silver, which then precipitates in the solution in a form that can redeposit on the film or paper, causing yellow/brown silver staining (which I've seen in video of reversing in-camera paper negatives for direct positive). This can seemingly be avoided by ensuring the emulsion isn't up in the bleach solution. There are other concerns with this process, however: one is that high strength peroxide (9%, 12%, or even 35%, for dilution to working solution) becomes hazardous to handle, and is a feedstock for certain improvised products that might lead to a visit from polite people in dark suits with a bulge under one arm, or very impolite folks with shotguns, battering rams, and body armor. Another is that peroxide is a well known bleach for organic pigments and dyes, and might damage the desired image dyes in color film stocks. I haven't been able to find any reports of anyone attempting to bleach color films with peroxide.
Potassium ferricyanide, either directly mixed with fixer or with a halogen donor, is a long-standing process for B&W; Farmer's Reducer and bleaches for color toning and for sepia/sulfide toning depend on this chemical. Kodak apparently once specifically called it out as an alternative bleach for their own color process (it's been rather a long time, though; this might have been for C-22 films). The primary concern with this process is that I've read that specifically Fuji films may experience a reaction that causes the base or one of the filter layers to turn a strong purple when exposed to ferricyanide bleach. This might be compensated with filtration for negative films, but obviously isn't acceptable for chromes.
And now we come to the question: has anyone here actually use either a ferricyanide or hydrogen peroxide bleach process on color films, to be able to report success, failure, or limitations?