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  1. #1

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    Color negative developer near to C41

    Here we go again…

    With some curiosity I checked different websites for colour negative developer formulations and some time ago I’ve posted (a bit cheeky) variations of developing solutions (which aren’t very well…). Very most public formulations are suspicious similar to formulations can be found in various patents by Kodak and Fuji concerning stability / speed / amount of concentrates of colour developers solutions. These formulations include typically CD4 0,015mol /Litre (4,38g/L) 1,3g NBR, 12mg KJ and a Ph of 10.00 (of course Potash ~30-37,5g, HAS ~2g, Sulphite ~4g, and chelating agents are present too)
    Developer of that kind is (in my eyes) only for research and meant as a comparative to set a stable basis. They do work, but not as a genuine C-41 developer should work. Even if the densitometer’s readings for speed and contrast for blue and green are partway OK, the red channel suffers badly. Taking some time to burrow through these scripts and search for changes in D.min/max under different formulations will show that too.

    Problems and Pitfalls:

    The bottom red sensitive, cyan coupling layer(s) do need more developing agent as usually listed.
    The middle green sensitive, magenta coupling layer(s) behave quite well but:
    The top blue sensitive, yellow coupling layers tend to be underdeveloped.


    Increasing the amount of CD4 in increments till 5,9 g/Litre (max. 6.2g) leads to an overall rise of density and contrast in an undesired manner. (You may remember, that’s the “photo techniques” formulation, all other found formulations are wrong as well (4.4/ 4.5/ 4,7/ 4,8 and 5g CD4))

    Than the spec. density of the solutions came into my mind, the usual 37.5 till 38 g /ltr. Potash leads (in my eyes) to an excessive diffusion pressure of alkali into deeper layers.

    The ph, with it’s most magnitude of influence has to carefully adjusted, usually at about 10.00 +/- 0.05 at 25°C (in the research /comparative formulations). For non chemists, equipped only with a quite simple pH meter, this is not a fun!!
    Forgetting the factor of maybe insufficient measuring equipment, I suspect this pH of 10.00 is too low.

    The amount of bromide is very important too, it does affect the first layer(s) more than the middle or bottom layers, which stay under influence of bromide, released by developing the surrounded layers. Bromide concentrations usually are given in mol/Litre. Be aware that KBR has to multiply by 1.16 due the different molar weight, if NBR is requested in a formulation!!

    Iodide (KJ) is till now 12mg/ltr. From former experiments with E-6 homebrew I know that blue-yellow axis can be controlled (within limits) via the iodide concentration in the FD, as well as in the CD. Maybe that’s typical only for E-6, and having read in PE’s valuable posts that the interimage effect and as a result sharpness is affected by iodide too, I’m till now a bit reluctant modifying the KJ dose.


    By the way, I’m doing tests with dry prewarm and wet prewarm /prewash. Since ever I’ve done a prewash, goanna stop this now. Diffusion speed for developing agent / alkali is increased for the cyan and magenta layers, R-G show an observable shift.

    So this is a funny game between pushing and pulling components, diffusion speed, and pH. At least the temperature stay’s constant…

    My last tests (No.19 – 22) were encouraging, the colour curves match well, exception still a slight but quite constant decrease of red. If using a prewash the results are very close to a former probe, developed with Flexicolor (prewashed too) but still different from my “reference minilab”. Maybe this is mainly the difference between rotary tube and leader card / or continuous developing machines, never have checked that before.

    … a week later…

    Anyway, after some nights in the dark, some thinking, spreading sheets of paper all over the flat, I’ve found a formulation that works VERY WELL.

    Very well means he colour curves shift not more than 0.09 from the green base. This is for the white pattern (HD) from the “Jobo test Chart” that one with 6 grey levels, RGB and CMY Patterns. This nearly reaches my minilab DIY reference.

    Density of HD is good, film speed either.
    I’m goanna try to load a scan of my densitometry values, but be aware, this is no conventional C-41 plot, I do it the way I do it for chromes too… values in braces are absolute, the other RGB values for field 1 till 6 are already subtracted from Dmin…






    This is the VERY BEST result so far, works much better than all other formulations I’ve ever tested. I call it C-25, for test run 25

    Here the formulation so far. In order to avoid the subsequent pH correction with sulphuric acid or KOH (which is a must-do in all formulations) I will try to include a carbonate/bicarbonate buffer system at the next run, but this may take some time...


    800ml Tab water
    1 ml Orwo A905 (wetting agent, can be omitted)
    2 g Calgon
    29g Potash (28 till 34 g are OK)
    4g sodium sulphite
    1.5 g potassium bromide
    12mg Potassium iodide
    2.5 HAS
    5.2 CD4
    Up to 1 Litre
    pH adjusted with KOH or sulphuric acid to 10.11 at 25°C
    Spec. gravity reads 1.035

    As you may see it would be make sense to increase CD4 in a very small fraction (maybe 0.1 till 0.15 grams, than maybe reducing the ph carefully to maintain HD at about 1.00

    If you are in some homebrewing, try this, you will not regret it.


    Comments welcome,
    Regards from Germany,
    Stefan
    Last edited by stefan4u; 10-13-2008 at 06:17 PM. Click to view previous post history.

  2. #2

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    There is a typo in the above formulation,
    1.2mg KJ has been used, not 12mg!!

    Regards,
    Stefan

  3. #3
    AgX
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    Congratulations!

    Quite a laborious experiment.

    -) it is always fine to have a working formula at hand from which to deviate for specific experiments.
    -) for those of us who undergo difficulties in obtaining industry C-41 chemistries, a formula for a homemade developer could be a solution
    -) some may consider doing so just for cost-effectiveness



    But keep in mind that Flexicolor sets the standard to which other companies have to design their films as long they want them to be processed with good results in chemistries who follow this standard.
    Thus films are optimized for a given process.
    (In theory there might be a C-41 film being processed in a custom made developer bearing even better result than Flexicolor.)

    You however designed a developer for a given film.
    It could be that with another film your results would not be that much in line with Flexicolor.
    Thus any comparative tests should be done with several types of C-41 films being processed.
    (I do this remark as you did not state how you ran your tests. Perhaps you already did so.)


    Seemingly this is a one-shot process at the moment.
    Are you thinking of doing several runs (time compensated or replenished) in future?

    How do you do the `dry pre-warm´? Just by letting the drum with film rotate for a while in the warming bath? Or do you use temperated air?

  4. #4

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    Dear AGX !!

    Definitely I do now that Flexicolor sets the standard, and I love it very much. Developers of other brands tend to give more contrast, this may be well in some situations, but gave me often difficulties during enlarging.

    I’ve done all this only to satisfy my curiosity about possibilities and probabilities of ingredients. Further there simply waits some stuff to be used .

    You are absolutely right, this is only for this type of film tested, and others may behave different. It’s only a hobby; I don’t have to earn my bread and butter this way.

    It’s used at a one way developer till now, just to reduce the variables. Replenishment seems not to make sense in the home darkroom, because of the lack of regular usage / regular “tank turnover” and intensified oxidation during drum processing.
    But the developer is not specially designed as one way, it’s not a “thinner one”, so reuse for one run should be OK with slightly prolonged time (~3:25 min.). As usual, use at least 200 - 250 ml for one film (135/36) and at its best at least 500 ml for better Temperature consistency in one run.

    That leads to your other question, the prewarm. As mentioned above I measures surprising differences in colour curves when using the prewetting/ wet prewarm. These differences are not stringent visible in a print, but one of the fluctuating influences I would like to skip. So a proper dry prewarm in temperate water / in the Jobo processor for about 20 min. in low volume clip developing conditions (200 ml) is necessary. As the volume of the developer increases it’s stability against temperature loss will increase too. Shorter dry prewarm times should be possible then …




    By the way “C-26” is on schedule with three changes :

    Minor decrease of sulphite to allow the lower densities so develop a touch more (from 4 to 3.5g).
    Minor increase of KBR (1,5 g to 1.7g) and KJ (1.2mg to 1.4 mg) to limits highlights
    The amount of CD4 stays at 5.2g , this is quite well working.
    Some buffer capacity for easy pH calibration is planned by adding
    bicarbonate. Readjust amount of potash for that…

    Regards from Germany,
    Stefan

  5. #5
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    IIRC, the pH is correct at 10.1, but the bromide seems too high, but I may be wrong. I have forgotten too much!

    All salts in the Kodak formula are Sodium salts and no potassium salts are used except for KI (KJ in German). So it is Sodium Carbonate and Sodium Bromide, etc..... Calgon is no longer used. Kodak uses Quadrofos or Dequest.

    I think the carbonate is low in your formula. That would cause low contrast.

    PE

  6. #6

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    Dear PE !!

    Thank you for „logging in“ , the ph at around 10.1 really works better than a ph above 10.00 or10.05. That’s something I couldn’t believe at first but looks proven now… The used bromide is potassium bromide, 1.5g are roughly equivalent to 1.3g sodium bromide.

    The usage of more effective anti chelating agents, like quadrofos or other EDTA salts, as you mentioned, will be better for sure. But we live in a region with quite soft water (haven’t delimed my teakettle for years) and longer shelf life of mixed product is not indented anyway.

    About the carbonate….
    This is something still mysterious, I’m still testing. But adding nearly 40g Potash alone plus all the other ingredients will inflate the gravity of the developer. I’m aware that data sheets are more intended to keep secrets, but there are a few things in common if you put some side by side.
    Flexicolor SM claims to have something about 18 till 22 g potash/litre combined with bicarbonate 3.6-7.4g7Litre. Flexicolor developer replenisher is stated with 22 -26g/Litre (diluted working tank solution), then next a “one phase” colour developer (Prime?) is stated with 23 g/L potash and 6,6g bicarbonate (all potassium). Is this coincidence that the amount of alkali salts is given at about 30g/Litre ??

    Anyway, I brewed up a solution with 24g potash (which was in fact low in contrast) and with 34 g potash/ Litre, wich was fine). Each half of unused solutions was mixed together that’s why “C-25” does have 29g Potash; the difference is measurable but marginal.

    Just this moment the Jobo fires up, prewarming the next batch, which do have 32 and 33g potasch/Litre and 1.5g sodium bicarbonate. Personally I do prefer more a soft working developer, the last edition was very close to desired.

    Well’ see what happens…

    Regards from Germany,
    Stefan

  7. #7
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    IDK why, but the NaBr is still high to me, but again, I may be wrong here. I also know that a carbonate series in the developer gives a contrast (gamma) series in the 3 layers. It is a matter of buffer capacity in the bottom layer making the cyan drop off faster. I seem to remember more carbonate than that. I'll have to test one of my patents, but IIRC, the carbonate in C-22 and C-41 were almost identical.

    PE

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    Hello again!

    “C-26” was a partway success , setting the pH with a combination of Potash and sodium bicarbonate works well so far.

    To be concrete:

    1ml A905
    2 g calgon
    32 g potash
    1.5 g sodium bicarbonate (has to be weigh out accurate!!)
    3.5 g sulphite
    1.7 g KBR
    1.4 mg KJ
    2.5 g HAS
    5.2 g CD4

    leads to a pH of about 10.12

    Increasing the Potash to 33 g/Litre gave me a pH of 10.14/10.15 .

    Because of working densitometer but rather “budget” ph meter with gel electrode, not approved for reductive photo chemicals, I do settle a measured ph of 10.14/15 at 25°C as my “aim”.

    Here is the bad news: Increasing the KBR and the KJ leads to the wrong direction, although reducing the sulphite, I lost about 1/3 stop (0.05 D). Balance of the Colour curves is untouched and still very good.

    Anyway, will use the residual “C-26” solution and do some more testing for slightly increased dev. Time and maybe again a prewash. The formulation is as close that I dare

    “C-27” with (again) slightly reduced KBR / KJ and maybe slightly upscaled CD4 (with necessarily upscaled potash) will follow…

    Regards from Germany,
    Stefan

  9. #9

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    Yesterday I brewed another batch, “C-27” and it turned out to be very close, I don’t think home brewing can get any closer!



    CD4 was increased to 5.3 g. Because of more acidic developing salt potash has to be increased as well to 34 g/ litre

    Potassium bromide was reduced in increments, 1,4 g/Litre seems to be the optimum amount.

    Potassium iodide was reduced again to 1.2 mg/Litre.

    Compared to “C-26” HAS was reduced to 2 g/Litre, and again a pH adjustment was necessary (grumble…) This time I increased the Sodium bicarbonate (Baking Soda) in increments up to 1.9g/litre lo maintain a pH of 10.16

    Developed clips where near perfection, high density regions as well as low density regions. Full film speed is reached, with steady going range of contrast. Because of beneficial influence of KJ in an amount of 1.4mg/litre in a former run, I just topped again 0.2mg/litre to the existing 1.2mg.

    The Jobo is prewarming now, but because of excellent former clips I dare to jump into the cold water and have filled a tank with 5 Films 5 x 135/27exposures (equal to 4 x135/36 exposures)

    This is my final developing solution: “C-27”

    800ml tab water
    1 ml A905
    2g Calgon
    34g Potash
    1.9g Sodium Bikarbonate
    3.5g Sodium Sulphite
    1.4 g Potassium bromide
    1.4 mg (!) Potassium iodide
    2g HAS
    5.3g CD4

    Up to 1 Litre,
    Measured pH is 10.16 at 25°C.
    As stated somewhere above the ph meter is a cheap one, so there may be a variance, suppose it’s around .03 till .05

    BUT whatever you do, pH has to be above 10.11 (measured with my unit 10.13), there is absolutely no chance to get a proper developed film with lower pH! Red will suffer badly!

    Therefore be accurate if scaling the ingredients, especially Bicarbonate and Potash, HAS and CD4. This formulation is intended to work without pH adjustment, that’s why I included the bicarbonate buffer. If proper ph measurement is available you may vary a bit, but have to readjust the ph again.


    Hours later...
    Uuups … Just measured the 5 films out. There seems to be a temperature inconsistency. It’s a different about 2/3 stops weather multitank 2 (with its volume of 270 ml) is used or the multitank 5 filled with a whole litre. Seeing this, I remember why I preferred the wet prewash for so long time…



    Anyway, a multitank 2, combined with a dry prewarm and about 250 ml (one film) of developer works definitely fine. The processors water jacket temperature is set to 38.4°C since ages; have to measure the difference of the temperature, after a minute or so, direct in the drums. Sadly my holidays are over, prints have to wait too.

    Regards from Germany,
    Stefan
    Last edited by stefan4u; 10-16-2008 at 04:50 PM. Click to view previous post history.

  10. #10

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    Really don’t want to bore anybody, but some words to disclose that …

    Because of the (always again) surprising influence of temperature drop during dry prewarm, versus inertia of bigger volumes I looked up through my negatives to find more comparatives.

    I’ve found films developed with Tetenal at 30°C for 8 min. which show a stronger overall colour deviation, that means colour cross over (magenta/green cast in the greyscale). But I’ve been able to enlarge quite good prints from these films, adapting the filtration that way these colour errors are more in the dark aereas…

    The time I’ve got Flexicolor in my hands, time of experiments began again. I tried different times (actually not too different, in the region of 3:20 till 3:30), dry and wet prewarms, all at my usual 38.4 °C . All data can’t be recovered, but consistency increased with bigger volumes, the last 2 years I always took as much as possible developer (~1Ltr/ for 5 or 6 Films).
    Worth remarking is that my usual proceedings (Drum processing, Flexicolor at 38.4°C jacket bath temp. for 3:20 min with a wet prewash gave me wonderful negatives. But the overall error is surprisingly higher (!) than with my actual home brews. For the most part this will be the influence of prewetting, (next to exceeding temp). But the error is not visible in, let’s say most prints (I’m attempted to say it’s not visible at all).

    If you want to try “C-27”, decrease temp about 0.5°C for amounts bigger than 250 ml (that is exact the temperature it should have) and maybe better use always the same drum / same number of reels / same amount of developer to get everything in control.

    Regards from Germany,
    Stefan

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