Recommendations of books on how to make C-41 chemistry?

While a difference in amount of acid molecules would certainly make a difference to the formula, there would be no significant difference if Kodak used a different counter anion than we assumed here. That's the beauty of the molar notation!

Also note, that the 1 CD4 + 1 counter anion version would be even weaker than the 2 CD4 + 1 counter anion version we all assumed, so my bets are firmly on 2 CD4 + 1 counter anion.

I just received permission from Stefan Lange (aka stefan4u, the creator of C-27) to post excerpts from his private communication to me. I contacted him some time ago after having issues with his C-27 soup - I always got rather high b+f in my negatives.

Here are his statements from several email exchanges, summed up and refactored to make them (hopefully) more readable:

1. Stefan warned be about incorrect pH readings of common pH meters in reducing bathes such as photographic developers. Apparently only special pH electrodes provide accurate readings in these environment. Adjusting a developer to published pH values may not give the correct soup despite proper pH meter calibration.
2. C-27 was optimized for a development regime in which the film tank was only preheated, but without prerinse. Tank temperature was therefore somewhat below 38°C/100°F during development. Stefan achieved optimal conditions for C-27 with 38.4°C water jacket temperature of his rotary processor.
3. Stefan freely switched between sodium and potassium salts of ingredients, adjusting only for number of mols. This is in stark contrast to (there was a url link here which no longer exists) that original C-41 CD contained only sodium salts except for Potassium Iodide.
   
4. Stefan created a C-29 version of his developer, targeted at film processing at correct process temperature. This version requires a water jacket temperature of about 40°C and effectively develops at 38°C/100°F:

Stefan's C-29 recipe for one liter of working solution goes like this:

A905 wetting agent	1ml
Calgon (Sodium Hexametaphosphate	2g
Potassium Carbonate	34g
Sodium Bicarbonate	2.1g
Sodium Sulfite anhydrous	2.8g
Potassium Bromide	1.6g
Potassium Iodide	1.4mg
Hydroxylamine Sulfate	1.8g
CD-4	4.6g

Rudeofus said:

Stefan warned be about incorrect pH readings of common pH meters in reducing bathes such as photographic developers. Apparently only special pH electrodes provide accurate readings in these environment. Adjusting a developer to published pH values may not give the correct soup despite proper pH meter calibration.

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Hi, I had mentioned something along these lines some time back. For many years the Kodak-recommended pH electrode was the Corning triple-purpose pH electrode, priced at near $200 US dollars, as I recall, back in the 1990s(?). I spent years as the QC manager in a large outfit including an in-house chem lab; we had access to levels of manufacturer support that few people would have, so these recs may not be commonly known. We literally "wore out" several research-grade pH meters over the years, to give an idea of how many readings we took.

I don't think these electrodes have been available for years, and the current recommended pH electrode is some version of a "Ross electrode," I think. Info should be available in the Kodak H-24 doc in the link below.

See my post #16 in this thread: (there was a url link here which no longer exists)

I was wrong about the Tosyl salt. IIRC it is one acid to one PPD.

Sorry.

PE

Update- after taking a look back at the H-24 document, I realize it may be hard to find the pH related info. So in my link to the 03 section of H-24, search for method "ULM-191-2," starting on about page 275 of the pdf file.

It looks like I was mistaken about Ross electrodes; the actual rec for "Glass pH electrodes" is Corning 476024, glass, rugged bulb, with a VWR part number given.

At EK, we used standard electrodes and if needed adjusted for concentration based on a chart supplied by the electrode manufacturer.

PE

PE, we always used the Corning triple-purpose pH electrode, alternating daily between two of them (a third, new one, was held in reserve). We were licensed users of Kodak formulary manuals, and pretty much followed the "bibles." We used literally thousands of gallons of replenishers daily, and with tight production schedules we didn't take any chances with the production work. We were also reading several dozen processor tank samples every day, and the seasoned samples are much more difficult to get stable readings. At any rate, we always stuck with the spec electrodes.

As a separate note, my only experience with "cheap meters:" back in the day when our company had a chain of 1-hour labs, our lab-supply rep came in with one of the early affordable portable pH meters. His idea was that we could equip our team of traveling field techs to assist their troubleshooting. I said, "let's see," and we compared a couple of developer samples with our high-grade meter vs his portable unit. I don't recall how different they read, but it was enough to be useless for us, and he was thoroughly embarrassed, saying he'd had no idea how bad it was.

Photo Engineer said:

CD4 comes in as many as 4 salts. One is 2 CD to 1 H2SO4, one is 1 CD to 1 H2SO4 .
PE

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PE, do you know the pKa for each acid form, or maybe relate a way to dissolve a bit of the CD in water and deduce by pH what form we have.

I have no idea. Sorry.

There are presumably melting point tables for them in Merck.

PE

Rudeofus said:

I just received permission from Stefan Lange (aka stefan4u, the creator of C-27) to post excerpts from his private communication to me. I contacted him some time ago after having issues with his C-27 soup - I always got rather high b+f in my negatives.

Here are his statements from several email exchanges, summed up and refactored to make them (hopefully) more readable:

Click to expand...

Thanks for the new formula. I'll comment:
1. I'm not sure of the extent of that effect. In general it is not easy to measure pH better than .05. Basic buffers go off when exposed to CO2 in air. The cheaper glass electrodes get a shift when in carbonates. I use ISFET electrodes which don't have the problems of glass. They still have a reference electrode that gives trouble with age though. I believe in making sure there is a good mix of carbonate and bicarbonate, so the solution is buffered and can be reproduced without a pH meter.

2. 38.3 to 38.4 deg C is what I use with 2 30 sec pre-wets at that temp. My bath is a bit hotter. This is the correct temperature and works properly with commercial developer according to control strips. I remember Stefan had some problems with low density when not pre-wetting. I have extreme precision mercury thermometers accurate to less than .1 deg. and calibrated a platinum RTD digital thermometer to the same accuracy which I mostly use for convenience.

3. Not sure if potassium vs sodium matters. The patent looked about like our formulas in that respect. The commercial one I have uses all potassium salts.

4. I'm not sure about this "correct" formula. Maybe he is running a bit hot now. If I try it I think it will give too low a density.

sfaber17 said:

3. Not sure if potassium vs sodium matters. The patent looked about like our formulas in that respect. The commercial one I have uses all potassium salts.

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There is some difference in ion diffusion speed between Na+ and K+. While the former is smaller by itself, it is more hydrated in solution and therefore less mobile, especially in gelatin. Companies selling concentrate solutions obviously prefer the latter, since in most cases the potassium salts are more soluble.

sfaber17 said:

4. I'm not sure about this "correct" formula. Maybe he is running a bit hot now. If I try it I think it will give too low a density.

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When it comes to "correct formula", I always have to think of Mr. Bill's comment #19 in (there was a url link here which no longer exists). There could have been some "correct C-41 CD" in Kodak's research lab, and there may be different "correct formulas" for home user kits, and there may have been yet another formula for labs with replenishment, trained lab rats and tight process control. As far as small volume home brewers are concerned, the most relevant formulas are somewhere in between KRL's soups and kit soups.

@sfaber17

High there… I‘ve done quite a lot testing when doing these homebrews, the C-27 is a quite close approach, or better, simply a good working composition.

But the usual pitfalls are remaining… Consistency of temperature is one of them. In the past I’ve used always two warm prewashes (still do it for E6), but remarked not only a slightly risen contrast but an increased error in R-G. When omitting the prewashes things got more harmonic, but the real processing temp. in the drum dropped.

To be concrete: I use an old Jobo Autolab 1, doing all this in the cellar at about 18°C surrounding temp. There is probably a greater temperature loss through the tubes/mechanic of the machine. Weight of one Spiral is about 70g, haven’t used film for the tests. Temperatures are measured with an electronic thermometer, pt100 electrode, 15 seconds after filling the drum and 3 minutes after filling. There are some errors in my setup for sure, but a tendency is visible.


Jacket bath 38.4°C, Developer 38.0°C

Multitank2, filled with 210 ml, one Spiral, 5 min. dry prewarm

After 15 sec. 36.0°C, after 3 min. 36.0°C
-----------------------------------------------------------------
Multitank 2 , filled with 330 ml, 2 Spirals, 5 min. dry prewarm

After 15 sec. 36.2°C, after 3 min. 36.0°C
-------------------------------------------------------------------
Multitank 5, filled with 640ml, 5 spirals, 5 min. dry prewarm

After 15 sec. 35.9°C (?), after 3 min. 35.5°C (??) something went wrong here…
----------------------------------------------------------------------
Multitank 5, filled with one liter, 5 spirals, one hour(!) dry prewarm

After 15 sec. 37,6°C, after 3 minutes 36,7°C (?)
---------------------------------------------------------------------
---------------------------------------------------------------------


Jacket bath 38.4°C, Developer 38.0°C, double prewash

Multitank2, filled with 270 ml, one Spiral, prewash

After 15 sec. 36.9°C, after 3 min. 36.5°C
-----------------------------------------------------------------------
-----------------------------------------------------------------------

Jacket bath 40.0°C, Developer 39.5°C

Multitank2, filled with 210 ml, one Spiral, 5 min. dry prewarm

After 15 sec. 37.8°C, after 3 min, 37.8°C


Multitank2, filled with 400 ml, two Spirals, 5 min. dry prewarm

After 15 sec. 37.6°C, after 3 min. 37.4°C


Multitank 5, filled with 640ml, 5 spirals, 5 min. dry prewarm

After 15 sec. 37.9°C, after 3min. 37.6°C




C-27 works pretty perfect at real processing temp. about 36.3°C, just half a degree more increases density about 2/3 stops and increases processing errors slightly.

So this soup is “stronger” than a “real” commercial C41 machine developer, but gives me perfect results under my special (undertemperature) conditions.


C-29, the successor of C-27, C-28 a, b, c, etc….

is less active and desperately NEEDS a proper process temperature of about 37.6°C-37.9°C. (Real temp. in the drum, NOT just filling temperature, but NO prewash!) Fine tuning belongs to you and your very special surrounding, but for me it works pretty perfect too… I would propose to use 400 till 500 ml for two films.

The formulation Rudeofous gave you for C-29 is nearly correct, but please decrease KBR to 1.5 g/L

All the best, stefan

sfaber17 said:

PE, do you know the pKa for each acid form, or maybe relate a way to dissolve a bit of the CD in water and deduce by pH what form we have.

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I have no pKa values for CD-4, but I have some numbers from T. H. James's "Theory of the Photographic Process 4th edition, page 317) for you, from which we can at least get some likely estimate:

1. CD-1 and CD-2 differ by an additional methyl group which CD-2 has on the ring right next to its unsubstituted amino group. Their pKa values are very very similar.
2. T-32 and CD-4 follow the same pattern: CD-4 has this extra methyl group, which according to PE provides extra dye long term stability.
3. Strangely, James lists only one pKa value for T-32, 6.90, while listing two values for PPD, ADMA, CD-1, CD-2 and CD-3. While the second pKa value varies quite a bit (6.20 - 8.14), the first one lies in a very tight range between 2.56 and 2.70.
   
4. With these things in mind, I would put the pKa values of CD-4 at 2.5-2.7 and the second one at about 6.9.
5. These pKa values differ a lot between reduced and oxidized form (pKa2 of T-32 goes from 6.90 ---> 8.90), and not always in the same direction: PPD pKa1 2.70 ---> 1.50, pKa2 6.20 ---> 5.75

stefan4u said:

@sfaber17

High there… I‘ve done quite a lot testing when doing these homebrews, the C-27 is a quite close approach, or better, simply a good working composition.

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Hi Stefan,
Thanks a lot for the data. I did similar tests with Multitank 2 but then have been developing with a 1500 series tank.
I'm using a Jobo ATL2200, which I would think would have similar effects as yours. I set the Temp to 38.4 but the water bath is then 39.0 due to a probably intentional offset, since that is what it takes to maintain the chemicals at the 38.4.
It could be I'm colder than I thought. After all, the developer has to be at or below the 38.4 C at the beginning. I became less interested after getting good results (with test strips) with the commercial developer at that point and may have standardized on a bit lower temperature, but I'd be surprised if it were 36.3 C. I'll look into it.
Could you share your source for CD-4 and if you know the exact form of the salt you have?

Regards,
Steve

Rudeofus said:

1. With these things in mind, I would put the pKa values of CD-4 at 2.5-2.7 and the second one at about 6.9.

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Thanks a lot Rudi. I'll try a pH test and see. Maybe I'll do a redox titration with iodine to get an equivalent weight also.

Every single product listing I ever saw for CD-4 used Sulfate as the anion. This leaves us with two likely options: the hemisulfate (CAS 28020-34-0, mol weight should be ~ 486, but is always listed as ~292) and the sulfate (CAS 25646-77-9, mol weight ~ 292). If CD-4 follows a similar pattern as CO2/HCO3-/CO3--, then I would expect pH of free base/hemisulfate/sulfate to be around 8-10/4-5/2, which should be trivially distinguishable even with pH strips.

CD-4 appears to see much more use in concentrate kits than as powder, and since these concentrate kits use the sulfate version to keep pH low, I would be surprised if anything but the 1:1 sulfate version would have ever been offered to anyone here.

Titration with iodide sounds like a difficult task to get right, since CD-4 has more than one stage of oxidation, and the oxidized form can couple with the reduced form or do other crazy stuff.

Kits are often made from the free base with sulfur dioxide added during manufacture to form the sulfite adduct. The alternative is to use one of the sulfate salts and add the SO2. This is all done under nitrogen. Much like making HC110.

PE

Photo Engineer said:

Kits are often made from the free base with sulfur dioxide added during manufacture to form the sulfite adduct.

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This is not what the respective MSDS say, even the Kodak supplied ones aimed at minilabs list the 1:1 sulfate version. Same thing is true for Tetenal.

Photo Engineer said:

The alternative is to use one of the sulfate salts and add the SO2. This is all done under nitrogen. Much like making HC110.

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The big difference between CD part 3 concentrate and HC-110 is their respective pH values. While HC-110 is quite alkaline and accepts SO2 without any issues, CD-4 1:1 sulfate has very low pH and won't chemically bind SO2, nitrogen atmosphere or not.

This patent lists components for a Kodak C-41 CD concentrate kit, and it appears that CD concentrate part 3 is made from CD-4 (sulfate or hemisulfate not specified), Sodium Metabisulfite and Sulfuric Acid.

I'm sure that technology marches on, and the process of using SO2 gas might have been difficult or might have yielded less favorable shelf life. I do know that this method was first used in B&W for HC110 and by another manufacturer for a liquid color kit. It was used by EK in color kits in the 70s.

PE

Dear sfaber17.

My old ATL1 does not have this kind of offset; it’s basically a CPP2 with ATL head mounted on. If I’m dialing 38.4°C I get 38.4°C in the jacket bath. The temperature in the chemical bottles is about half a degree Celsius lower…

CD1, CD2 and CD3 I bought from German suppliers (where I live), some of them from former East German companies.

CD4 was bought in Canada. Simply because it was a LOT cheaper, all taxes/shipping included, I will never understand such things…

I think it was JD Photochem, but they stopped selling CD4 some years ago… It is / was 4-(N-Ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine sulfate, Cas:25646-77-9.

India or China would be the places of my interest, if I have to refill my freezer again for a reasonable price.

All the best, stefan

Rudeofus said:

CD-4 appears to see much more use in concentrate kits than as powder, and since these concentrate kits use the sulfate version to keep pH low, I would be surprised if anything but the 1:1 sulfate version would have ever been offered to anyone here.

Titration with iodide sounds like a difficult task to get right, since CD-4 has more than one stage of oxidation, and the oxidized form can couple with the reduced form or do other crazy stuff.

Click to expand...

Yes, I that makes a lot of sense. I tend to agree it almost has to be the acid sulfate version, which means the MW of 292 should be right. Maybe the iodine would work, it worked OK for ascorbic acid which does complicated things also.

As far as I know CD4 used in “usual” C41 formulations is always xyz-methylaniline sulphate. But it must be kept under low pH (about 2) to keep it stable in a solution. “Usual” formulations are the three part mixes.

The one part formulations (Prime for example) do have a much higher pH and use the free base as developing agent. The free base will be won through mixing CD4 with a 50% solution of NaOH and diethylene glycol. A precipitate will fall down and filtered out. Et voila, there is the free base

All the best, stefan

And the free base darkens and turns to tar very rapidly. I've done that with CD1, CD2, CD3, CD4, CD5 and CD6! (Surprise, there was a CD5)

But then that is why single part kits are not very useful IMHO. They would tend to go bad.

PE

This has been a great thread. The patent reference, Arcus high pH formulations, C-29, revisit tank temperature and pre-wet. I mentioned before I used 38.4 deg. C, but found lately I'm set down at 37.8. After measuring the tank temperature of the 1520, it is 37.2 at 15 sec and 37.3 at 3 min. My previous tests also showed the tank maintains its temperature well or increases slightly. If I kept the 38.4, I'd be at the right temp. My commercial high pH Arcus formula developer might react differently than the 10.1 pH formulations to temperature and pre-wet. I wonder if the 1520 tank has lower effective agitation than a 2800 series due to the diameter difference. Maybe I'll get some 35mm reels for 2800. I only have 4x5 with 2800 series.

I made some C-29 to compare to C-27 using test strips. The C-27 was 2x pre-wet at 37.2 deg tank temp. The C-29 was 1 hr pre-warm, no pre-wet. 37.8 deg tank temp. The C-29 has substantially less CD-4, closer to some other formulas like Dignan. It has less sulphite and only a bit more bicarbonate, which leaves the developer substantially more basic than C-27 due to the lower amount of acidic CD-4. The C-29 has an increase in the green channel over C-27, which is an improvement, but it suffers from too high a blue contrast on the Fuji, although the Kodak is OK and a bit of an improvement overall over C-27. The C-29 Dmin is a little better but the contrast is more important I think. The values in parenthesis indicate the control limit was exceeded.

C-27 C-29
Fuji r,g,b r.g.b
Dmin 3,2,(8) 2,-2,5
LD 0,-5,(15) 1,7,(12)
HD-LD -7,0,7 -4,5,(13)

Kodak
Dmin -7,-5,0 -9,-8,-3
LD -1,-6,(11) -1,3,(9)
HD-LD -2,6,-3 1,2,5

pH 10.12 22C 10.38 21.3C


The Fuji test strips/film are more sensitive to blue. The Kodak strips had an anomalously high Dmin on the standard strip, so they show lower values than they should I think.