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C41 Formulas

Photo Engineer

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Here is what I have found. I have 3 versions of what are reported to be C41 formulas. They vary quite a bit, so IDK if Kodak researchers are tinkering or what.

The newest fix contains Ammonium Thiocyanate to speed fixing. The newest films are harder to fix. This is the original fix.

The newest stabilzer uses only a biocide and a surfactant. In either stabilizer or final rinse, you can substitute Photo Flo for the surfactant noted.

These pretty much match the original formulas we used during R&D of C41 products in the '80s.


Enjoy.

PE
 

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Well, well, well. I know I put the bleach in there but it isn't there, so here it is!

The file was corrupted somehow. Twice!

PE
 

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Last edited:
Thanks. What about original E-6, K-14 and other kodak recipes?
 
Boy, that sodium sulfite is severely restricted in color formulae! Even after factoring-in the metabisulfite. Apparently there is a tug-of-war between the developer being able to do its job (without oxidizing) vs the sodium sulfite assassinating it. - David Lyga
 
That is what I said: it is restricted BECAUSE you cannot use large portions. Case settled. - David Lyga
 
The E6 exact formulas are not easily available. I'm trying to get them. The Kodachrome formulas are well known from the work here and in the patent.

PE
 
Yes the sulfite interferes with the dye formation. For the same reason sulfite must be kept to a low level in staining developers those using catechol or pyrogallol.
 
Photo Engineer said:
The newest fix contains Ammonium Thiocyanate to speed fixing. The newest films are harder to fix. This is the original fix.
Click to expand...

Ron,

Do you have the newer fix formulas?

Are these formulas suitable for modern films, such as Portra and Ektar?

Thanks in advance,
Flavio
 
Before B&H stopped carrying Flexicolor fixer I bought a five gallon size (about $50) and went to NYC to pick it up. a block from Penn Station. This was about four years ago. I am telling you that this concentrate is the best fixer Kodak ever made, and I use it for B&W as well as C-41. It does not smell and the concentrate stays clear, even after four years. - David Lyga
 
The fixer formula above should work for all films, but for C41, use 6 - 8 minutes at 100F as per the original EK instructions. The more modern fixer can cause blistering or reticulation when used with some 3rd tier films. This is due to the swell that can be induced by Thiocyanate in some gelatin - hardener combinations.

PE
 
I got a large quantity of C-41 fixer concentrate from the lab I work at when it stopped processing film in late 2009, and what I have not used is still as clear as crystal (stored in glass jars, filled). As others do, I use it for both both b&w and color.
 
I am surprised to see a combination of Ferric PDTA and Ferric EDTA in this C-41 bleach. Can you please tell me what's up with that? Would a bleach using Ammonium Ferric PDTA only have been too powerful for C-41 emulsions of that time?

Also, do you know the pH of this bleach? pH is listed for CD and fixer, but strangely not for bleach.
 
It is right there in the table, pH 7.05. The mix gives the bleach a tad more oxidation power.

PE
 
Photo Engineer said:
It is right there in the table, pH 7.05.
Click to expand...
The way this pH 7.05 is stated suggests to me that it applies to the Ammonium Ferric EDTA, not to the whole bleach. It would also be quite surprising if Kodak used a bleach near neutral pH.
 
Hmm, you are right, but then the blix and bleaches I know of are all about 6.5 so that would probably be a good starting point. I have no other information at this time.

PE
 

Thanks for the information, Ron. I'll be trying these formulas as soon as I can. I have most of the chemicals needed. I just have to source some stuff like PDTA and Ferric Amonnium EDTA.

Cheers,
Flavio
 
Photo Engineer said:
Hmm, you are right, but then the blix and bleaches I know of are all about 6.5 so that would probably be a good starting point.
Click to expand...
The few commercial bleaches, for which I found MSDS, show pH much lower than 6.5, something more like pH 4.2 - 4.5. Obviously you need pH 6.5 for BLIX, but for bleaches you can take advantage of the much higher activity of Ferric EDTA/PDTA at lower pH. Another advantage of bleaches at low pH is a great reduction in washing effort between CD and bleach, in many cases one can go directly from CD to bleach.
 
You are correct. Kodak Bleach III is about 5.5 though, and I know that pH 4.5 bleaches are possible. I have formulated them myself. Don't try to make a blix at that pH though! Oh, and remember that the dyes do not necessarily like wide pH swings.

PE
 
Photo Engineer said:
Oh, and remember that the dyes do not necessarily like wide pH swings.
Click to expand...
Wouldn't a stop bath, which you, too, recommend for C-41, typically operate at pH 4.5 or lower? Unbuffered Acetic or Citric Acid stop bathes would be substantially lower in pH.

The real lower limit for bleach pH, that I have observed, is solubility of chelating agent. EDTA, PDTA are only soluble in quantity above a certain pH. Both Ferric EDTA and Ferric PDTA bleaches will work at pH 4.5, though, at least from my own tests so far. I also vaguely remember reading a bleach III MSDS which stated pH 4.2 - 4.5. I'll try to locate this MSDS ...
 
Well, the replenisher is listed as pH 3.3 and the starter is pH 13. The working solution has been reported from 4.5 to 5.5 depending on version. I have at least 2 versions in my darkroom.

PE
 
PE,

Glad you talked about starter and replenisher.

The formulas you published are working solutions and should not be replenished, right? I mean, are these meant to be used "one-shot"? How many rolls would, let's say, one liter of developer would yield?

Do you have the Kodak documents for original C-41 process — which, at least theoretically, would apply to the formulas you posted?

Cheers,
Flavio
 
Flavio, I have published the EK process directions time after time. Sorry. As for the solutions I published, they are supposed to be one-shot.

PE
 
After trying a dozen or so formulas with test strips I was expecting this formula to have low activity, low contrast in red and blue due to the low pH of 10.05 or so. I just made some and ran the test strips and it did give similar results to one I ran earlier that had a similar pH and 4.75 g of CD-4. The results of this formula (substituting with KI and NaHCO3 equimolar amounts, and not using the PDTA) are:

Fuji strip: R,G,B
Dmin 0, -.02, +.06
LD -.05, -.12, +.07
HD-LD -.17, -.10, 0

Kodak: R,G,B
Dmin -.09, -.08, -.01
LD -.05, -.10, -.05
HD-LD -.10, -.01, -.20

From tests by Stefan and myself, it seems we need a pH of 10.2 to get good red contrast levels.
Interestingly, this formula has the same iodide, bromide and HAS concentrations as my best formula, but I had to increase the CD4 to 5.2g and run it at pH of 10.2. It seemed to help to also use the higher levels of carbonate and sulfite found in the phototechnologies formula. Stephan's best (C-29) is closer to this (OPs formula) in that it has fairly similar carbonate and sulfite and CD-4 levels but runs it at pH of 10.4 to get the contrast up to standard levels and balance. I use a commercial CPAC developer that is at least that high a pH and has an even higher concentration of CD4 I believe, and it has the best test strip results of any I tried, so maybe processes have evolved toward the higher pH.
 
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