C41 Formulas

Photo Engineer said:

I myself don't mix from scratch! My time is more valuable than that and I prefer buying kits off the shelf. I understand why some prefer mixing and do it yourself, but if you factor in your time and other minor (or major) glitches that might take place, it really isn't worth it.

There probably will be a firestorm over this one.

PE

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Never be afraid of firestorms PE.
As I have noticed from the past you may have a very well funcioned "firewal" against it.
I've to install this to.
Because firestorms came allways on you if you are not prepared to them.

with greetings

Photo Engineer said:

Ferric Hydroxide does not react with EDTA at room temperature and pressure. It requires a quite elaborate method of manufacture...

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Photo Engineer said:

... I don't know if Ammonium Bicarbonate could be used. I never tried it...

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Well, I did some experimentation regarding Ferric Ammonium EDTA synthesis and things are looking good. I started by precipitating EDTA free acid from EDTA 4Na, using sodium bisulfate. I also precipitated ferric hydroxide from ferric chloride hexahydrate using sodium carbonate. I noted the ferric chloride quantity I used, because the resultant sludge can't be weighed in order to get a precise amount. All of it would be used as is. Tiny scale experiments confirmed that ferric hydroxide can react with EDTA free acid, but the solution must reach the boiling point. Anyway, I loaded the ferric hydroxide sludge to a borosilicate glass beaker and added some water. I heated it to loosen the clumps and most of them were gone. At that point I added the EDTA I'd have to use and started stirring. As the mixture was getting close to the boiling point, the rusty bits of ferric hydroxide seemed to disappear slowly. At that point I added what ammonium bicarbonate I'd have to use and it fizzed vigorously. In hindsight, that's probably not the right thing to do.

I probably should have let all the ferric hydroxide react with the EDTA and even add more EDTA if some bits remain for a long time. Then I'd have to add the ammonium base, be it bicarbonate, or ammonia solution. I used ammonium bicarbonate and this was probably not that good an idea as I thought it was. You see, ammonium bicarbonate decomposes at 41,9°C, so adding it to a very hot solution makes it fizz a lot. So, this gave me the impression that even more ammonium bicarbonate was needed. Anyway, to cut a long story short, I added an excess of it and probably an excess of EDTA, but all the ferric hydroxide was gone at the end. I also boiled the solution a bit, in order to drive any dissolved ammonia off the solution. After it cooled a bit, I filtered it with a coffee filter, but nothing was caught there. The solution had a deep ruby red colour and it was very clear, although rather hard to judge as can be seen at the following photo:



Based on my calculations, this has about 12% w/v ferric ammonium EDTA dihydrate. After the solution had reached room temperature a pH measurement revealed that in was nearly pH neutral. At this point I used some of it to make 50ml of a bleach solution. The formula I used was the one in (there was a url link here which no longer exists) by Heinz Anderle, but with some modifications. I didn't add any EDTA 2Na and didn't use nitric acid to adjust pH. 60% acetic acid was used instead. For a bleaching test I used a scrap leader of Tri-X. At 26°C it took about 6' to completely bleach the film (fixing for about a minute in Agfa 304 cleared the film). I don't know how good a bleach it will be for C41 or E6. Lacking an accelerator*, it means that it might not be as good as a commercial one. But still, it was fun and a very educational experience.

* The formula by Heinz doesn't have one either, but the pre-bleach solution does.

I'm sorry to say that the reaction did not go for me. The solubility product for the hydroxide is so high that the complexation is difficult to achieve. Have you checked your film for stain? What I did get to "work" caused a high stain to remain in the film due to iron.

However, I'm happy for you if it all works out.

PE

No stain as far as I can see PE. It has the normal gray tint that the base of Tri-X has.

I'm surprised that they reacted at all. Keith and John (holders of the patent for making bulk NH4FeEDTA) had the same problem until they used high temp and pressure. Best of luck. I'm glad I was wrong. It opens up a lot for people.

PE

Photo Engineer said:

I'm sorry to say that the reaction did not go for me. The solubility product for the hydroxide is so high that the complexation is difficult to achieve. Have you checked your film for stain? What I did get to "work" caused a high stain to remain in the film due to iron.

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The reaction wouldn't have happened with dry Ferric Oxide/Hydroxide, but it does seem to happen with very hydrated Ferric Oxide/Hydroxide. There are procedures for making Ferric Ammonium Oxalate, which also start with fresh and wet precipitate. The same reaction occurs only extremely slowly (think: years) with dry Ferric Oxide.

Rudeofus said:

The reaction wouldn't have happened with dry Ferric Oxide/Hydroxide, but it does seem to happen with very hydrated Ferric Oxide/Hydroxide. There are procedures for making Ferric Ammonium Oxalate, which also start with fresh and wet precipitate. The same reaction occurs only extremely slowly (think: years) with dry Ferric Oxide.

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Did you try boiling the mixture? Some reactions need elevated temperature to take place.

Anon Ymous said:

Did you try boiling the mixture? Some reactions need elevated temperature to take place.

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I have not heated the mixture, wanted to look how long it takes at room temperature.

RPC said:

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.

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Just to get more sure as sure - or let me
say I am interested in addition to your
experience.
So let me ask : The fixer concentrate shell live should be more then one decade ....with a little luck (in unopened
original containers)...you got from your
lab.
How long (perhaps estimated) should be
the shell live of your deluted working fixer solution when you have it used only one time or twice?
Is it indeed also to many years like bw
fixer ?
I know this is an older thread but never
mind aboud. ....your experience to
shell live is also a little more.

with regards

Photo Engineer said:

I'm surprised that they reacted at all. Keith and John (holders of the patent for making bulk NH4FeEDTA) had the same problem until they used high temp and pressure. Best of luck. I'm glad I was wrong. It opens up a lot for people.

PE

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Well, you were right about ferric oxide not reacting under normal pressure. I bought some red ferric oxide and tried to make NH4-Fe-EDTA, but failed miserably. Unlike the hydroxide, it's practically useless. Meanwhile, I found the US patent 3767689 and it really is interesting for anyone who'd like to synthesize NH4-Fe-EDTA. One of the patent holders is John J. Surash of EK. The patent mentions that ferric hydroxide can be used (but it's a rather messy and laborious task), but some forms of ferric oxide (brown and yellow) can be used with a bit of difficulty. Sadly, the "rouge" variety isn't one of them. The most surprising thing though is that ferroso-feric oxide (Fe3O4, black iron oxide) is the ideal form of iron oxide for this purpose. It reacts easily and at below boiling point temperatures. Now, many might wonder about the iron(II) content in the resultant product, but this can be oxidised to iron(III) by bubbling air through the solution, in the same manner that a bleach is aerated periodically.

Rudeofus said:

... You can make EDTA free acid from EDTA Disodium Salt by dissolving as much as possible in a liter of water, then adding a strong acid like Sulfuric Acid or Hydrochloric Acid...

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Hello Rudeofus

I've tried the EDTA 4Na + sodium bisulfate method in the past and worked nicely. I wanted to try precipitating EDTA using hydrochloric acid, mainly because of the quantity and solubility of the byproducts, so bought some from the super market (no chemical retailers nearby). It was supposedly a 16% w/w solution, but a quick density measurement revealed that it's more likely a 7-8% w/w solution. Anyway, I used an excess of HCl for the EDTA 4Na I used, but got no precipitate whatsoever. The solution was highly acidic, in the 1 to 2 pH range. Any idea why it failed?

HCl should go much lower in pH than 1-2, and so should EDTA in its free acid form. You may have underestimated the amount of HCl you need to precipitate the EDTA. But even at pH 2 you should already see some precipitate ...

One of my observations was that precipitation did not happen all at once, it's almost like you need some seed crystals to precipitate EDTA in quantity. Maybe this takes longer with HCl. You could try adding just a bit of your Sodium Bisulfate, then add Hydrochloric Acid in sufficient amount to get pH below 1.0. All this is pure speculation, though, I have so far avoided HCl due to its pungent stench.

Rudeofus said:

HCl should go much lower in pH than 1-2, and so should EDTA in its free acid form. You may have underestimated the amount of HCl you need to precipitate the EDTA. But even at pH 2 you should already see some precipitate ...

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Oh, the combined EDTA-4Na + HCl had a pH of 1 to 2, not HCl alone.

Rudeofus said:

One of my observations was that precipitation did not happen all at once, it's almost like you need some seed crystals to precipitate EDTA in quantity. Maybe this takes longer with HCl.

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Yes, I've noticed that too. There has to be a nucleation site for crystallisation to happen and it takes some time to kick off, but it starts in less than a minute when using bisulfate. When I tried HCl, I left the combined solutions for more than 15', but still nothing had happened.

Rudeofus said:

You could try adding just a bit of your Sodium Bisulfate, then add Hydrochloric Acid in sufficient amount to get pH below 1.0. All this is pure speculation, though, I have so far avoided HCl due to its pungent stench.

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Funnily enough, I had added a pinch of bisulfate after EDTA precipitation failed and it produced some precipitate almost immediately.

By adding solid, you create nucleation sites that accelerate the precipitation process. You can do the same thing sometimes by scratching the sides of the container with a glass rod.

PE

Photo Engineer said:

By adding solid, you create nucleation sites that accelerate the precipitation process. You can do the same thing sometimes by scratching the sides of the container with a glass rod.

PE

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Just had another try with HCl today and added a tiny bit of EDTA free acid to the final solution. It seemed to help crystal formation, but the whole process was more like a crawl. Then I thought about cooling the solution and it did seem to make quite a difference. Definitely not as fast as adding sulfuric acid or sodium bisulfate, but in the end it seemed to produce the amount of precipitate that it should (by eyeballing it that is). Treating the leftover precipitate in the beaker with some sodium carbonate solution made it dissolve, just like EDTA would. Addition of water alone didn't dissolve it.

So, it seems that EDTA free acid was produced after all, but it's not a very convenient method. I'd stick with sulfuric acid, or sodium bisulfate.

Anon Ymous said:

Oh, the combined EDTA-4Na + HCl had a pH of 1 to 2, not HCl alone.

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I realize that, yet pH > 1 looks odd to me. When I mix my bleach from EDTA, Ferric Nitrate and increasing amounts of NH3, pH starts somewhere at 0.9. This is the pH you should be aiming at with your HCl.

Anon Ymous said:

Funnily enough, I had added a pinch of bisulfate after EDTA precipitation failed and it produced some precipitate almost immediately.

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If you suspect that the Sulfate anion accelerates precipitation of EDTA, you could verify this by adding either Sodium Sulfate or plaster of Paris.

Rudeofus said:

I realize that, yet pH > 1 looks odd to me. When I mix my bleach from EDTA, Ferric Nitrate and increasing amounts of NH3, pH starts somewhere at 0.9. This is the pH you should be aiming at with your HCl...

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Let me clarify things a bit...

In cases like that, I'm too lazy to actually grab the pH meter, I just use some indicator paper strips. I don't recall the actual colour, it was few weeks ago, hence the 1-2 pH range. It might as well be <1, these things aren't very accurate anyway.

The C41 formula in the OP makes use of DTPA 5Na as a chelating agent, something that the average hobbyist can't source. Am I right in assuming that not using any of it, or substituting it with hexametaphosphate will result in a significant pH mismatch?

I would certainly assume so, especially given how much of this compound is listed. In case this helps: acid dissociation constants for DTPA are pKa1 = 2.14, pKa2 = 2.38, pKa3 = 4.26, pKa4 = 8.60 and pKa5 = 10.53. The pentasodium salt of DTPA is therefore very alkaline. About possible substitutes:

• The values for EDTA are pKa1 = 1.99, pKa2 = 2.67, pKa3 = 6.16 and pKa4 = 10.16, therefore I would expect a good match between Na5-DTPA and Na4-EDTA. EDTA will properly sequester Ca2+ and Mg2+ at the pH of C-41 CD, but it is known to not prevent Fenton reaction with Iron/Copper impurities, so you should expect shorter shelf life with EDTA than with DTPA.
• Hexametaphosphate is more or less neutral, so a pH adjustment will be necessary. Hexametaphosphate is also known to hydrolyze in alkaline environment, so shelf life will be poor. It also doesn't help with Iron or Copper impurities.
• Suvatlar sells Etidronic Acid under some Fotoplex name, this compound is compatible with photographic developers and it stops Fenton reaction. It does lead to white precipitate in hard water, therefore formulas based on Etidronic Acid use another sequestering agent for water hardness (IIRC it was EDTA). Obviously a pH adjustment will be necessary, but with Etidronic Acid plus EDTA you should get comparable shelf life properties to DTPA.

Rudeofus said:

I would certainly assume so, especially given how much of this compound is listed...

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And a 1% solution of it has a pH in the range of 11 to 13 from what I've found...

Anon Ymous said:

And a 1% solution of it has a pH in the range of 11 to 13 from what I've found...

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Which nicely lines up with the pKa5 of this compound. pH is not the only thing, though, I'd guess that even 0.01% solution would have at least pH 11. You need to look at buffering, too, and at 8 g/l compared there will be a noticeable effect, even if the soup contains roughly five times the weight and about 20 times the ion count in carbonate.

As long as the final pH is the same, there should be no problem.

PE

Photo Engineer said:

As long as the final pH is the same, there should be no problem.

PE

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And what about substituting Potassium salts with equimolar amounts of Sodium salts?

That might give you a different result.

Hello all...

I made a modified version of this C41 developer formula lately and used it to process a roll of Kodak ColorPlus 200. I substituted potassium carbonate and bicarbonate with equimolar amounts of sodium carbonate and bicarbonate. Likewise, I used potassium bromide instead of sodium bromide. Sodium hexametaphosphate (2g/l) was used instead of DTPA-5Na. This caused a large pH mismatch, IIRC 9,7 instead of 10, so I had to use about 1,1g/l NaOH to correct it. I shot several frames of a gray card with progressively increased exposure (EV -3 to +5) under daylight and took density readings of them with my scanner. As we can see from the characteristic curve, it seems that the red channel lags behind:



Of course, my equipment isn't that good and my data should be taken with a grain of salt, but the red channel contrast mismatch is probably real. To be honest, I've done the same with the Rollei Digibase C41 kit (supposedly made by Fuji) and commercially processed film and all of them showed the red channel lagging behind to some extent. This may be a concern if you print with an enlarger, but it's IMHO not a big deal if you're scanning. My scans from this film look nice (always IMHO) and a sample can be seen below: