Making and Maintaining Bleaches for E-6 Process

[Rudeofus]

Thank you.
In theory, things seem to look good. Let's see how it works out in practice. I've placed the order, so I'll probably have everything I need by tomorrow.
I assume I should start with the EDTAs when dissolving everything, right?

You'll be fastest if you dissolve the EDTAs into a mostly neutral or even somewhat alkaline solution. Don't be too high with pH, otherwise Ferric Hydroxide will precipitate, which may be difficult to get back in. I suggest you build a buffer around pH 5 with Ammonia and Acetic Acid, then add the Ammonium Bromide, then the Sodium Ferric EDTA and the Sodium EDTA. Only then bring pH down to 4.5.

 

[Josaw98]

So, unless I made a mistake somewhere (with the help of AI), I would need about 65 g of Sodium Ferric EDTA.3H2O. It seems the only inconvenience will be that I won't be able to make a concentrate (solubility in water: 75 mg/ml at 20°C), but on the other hand, it will be inexpensive and there will be no problem sourcing the ingredients.

Hi, I can finally answer. I had problems logging into my account.

I'm sharing my experience using this product. In my country, it's sold as a 13% iron chelating agent. Does it work? Yes, it does, but the processing times are very slow. For color negative film, you'll need processing times between six and eight minutes. For color positive film, you'll need between 12 and 14 minutes.

A problem is that when left to stand and cool, a crystallized precipitate forms at the bottom of the container. I was using 120 g per liter of solution, and it needed heat to dissolve. The crystallization I mentioned earlier was perhaps a result of using sodium bromide. I never tried this compound using potassium bromide or ammonium bromide. Since I didn't like the long processing times for the film, and I wasn't entirely satisfied with that crystallization, I decided to return to EDTA ferric ammonium .

This message isn't meant to discourage you from using this method, but I wanted to share my experience. As I mentioned, the product works, and if you don't mind long processing times, this is a good alternative.

 

[lamerko]

Thanks for sharing your experience.
First of all, I should clarify that all these efforts are aimed at making an E-6 bleach, which simply isn't sold here.
Ideally, it would be best to use Ammonium Ferric EDTA, but unfortunately the available options are very limited and quite expensive. That's why I was happy to find convenient and inexpensive sources of Sodium Ferric EDTA (13% Fe-EDTA).
You mentioned using 120 g per liter, but the datasheets indicate a solubility of 75 g per liter at 20C. The crystalline form (.3H2O) in which it is sold should have slightly higher solubility, but it still exceeds the limit - so it's normal for it to crystallize once it cools down. My calculations showed that I would need around 65 grams. I'm planning to compensate for the speed issue by using ammonium bromide.
I ordered 2 kg of 13% Fe-EDTA two days ago, but the shipment seems delayed - hopefully it will arrive tomorrow. I already have ammonium bromide on hand.
If I get the EDTA by the weekend, I'll run a few tests and share the results.

 

[Josaw98]

Yes, it was quite surprising to me to see, that one could replace Fe(NO3)3 * 9 H2O powder gram for gram with Ferric Chloride 40% w/w solution, but the numbers do add up quite accurately.

There is a slight excess of EDTA compared to Ferric content, that's quite intentional. One of Ron's patents specifies that EDTA excess to be somewhere around 1%, and Ron was quite adamant about that this was really important to make bleaches work well.

Adding to this, I've found another economical way to obtain a working iron source for creating the complex. Ferric sulfate can be used; it's a slightly cleaner way to form ferric ammonium EDTA. However, where I live, the price of ferric sulfate is similar to that of ferric nitrate. Luckily for me, I discovered that ferrous sulfate is very inexpensive, $1 per kg, and can be oxidized using persulfate, preferably in its ammonium salt form, but the sodium salt works just as well. Here's the reaction:

2FeSO4 + (NH4)2S2O8 → Fe2(SO4)3 + (NH4)2SO4

The process is as follows:

92.1 g of ferrous sulfate are dissolved in 200 ml of water, and separately, 40 g of ammonium persulfate are dissolved in 100 ml of water. The ferrous sulfate solution is heated to 40°C, and the persulfate solution is added dropwise. The reaction will generate heat and reach a temperature slightly above 60°C. A slight excess of persulfate is used to ensure that all the iron(II) is converted to iron(III).

112 g of acid EDTA are dissolved and neutralized with ammonia until a pH of 6.8 is reached. Then the ferric sulfate solution is added little by little to create the complex. The pH will gradually decrease. When it drops to 5.5, ammonia is added drop by drop to reach pH 6.8. This process is repeated until the ferric sulfate has fully adhered and the pH is adjusted to 6.3 for a negative color and 5.8 for a positive color.

 

[Josaw98]

Using sulfate instead of chloride ensures the solution is free of halides other than bromide. Although ferric chloride works excellently, I haven't noticed any visual difference between the two. I'm offering another alternative for those who want to formulate their own bleach, and let everyone make their own decision.

 

[Josaw98]

Thanks for sharing your experience.
First of all, I should clarify that all these efforts are aimed at making an E-6 bleach, which simply isn't sold here.
Ideally, it would be best to use Ammonium Ferric EDTA, but unfortunately the available options are very limited and quite expensive. That's why I was happy to find convenient and inexpensive sources of Sodium Ferric EDTA (13% Fe-EDTA).
You mentioned using 120 g per liter, but the datasheets indicate a solubility of 75 g per liter at 20C. The crystalline form (.3H2O) in which it is sold should have slightly higher solubility, but it still exceeds the limit - so it's normal for it to crystallize once it cools down. My calculations showed that I would need around 65 grams. I'm planning to compensate for the speed issue by using ammonium bromide.
I ordered 2 kg of 13% Fe-EDTA two days ago, but the shipment seems delayed - hopefully it will arrive tomorrow. I already have ammonium bromide on hand.
If I get the EDTA by the weekend, I'll run a few tests and share the results.

I'll be waiting, best of luck!

 

[lamerko]

I'll be waiting, best of luck!

Thank you!

 

[Rudeofus]

Using sulfate instead of chloride ensures the solution is free of halides other than bromide. Although ferric chloride works excellently, I haven't noticed any visual difference between the two. I'm offering another alternative for those who want to formulate their own bleach, and let everyone make their own decision.

I am not exactly sure, why an extra halide should be a detriment to bleaching ... whereas the sulfate is known to reduce emulsion swelling and therefore reduces diffusion speed, which translates into a loss of bleach speed.

If you have results showing, that the chloride does something the sulfate doesn't, then I would love to hear details.