Blix for ECN, C-41 and E-6

[The Black Pharaoh]

Praise Cthulhu!

Here's a Blix recipe that's worked for me with ECN, C-41 and E-6.

Distilled water - 700ml.

Amm Thiosulfate - 150g
Sod Carbonate - 8g
Na Fe EDTA - 58g
Sod Sulfite - 17g
PDTA - 13g
Mercaptotriazole - 100mg.

Distilled water to make 1000ml.

In my experience, the above formula has been bleach/fixing all the above mentioned films in 10mins @ 38c.
Try it out!

Thanks to @Rudeofus, PE, the usual suspects.

Please note, i do NOT have scientific instruments to test it fully. To my naked eye, i see no remaining silver left, even with Ektachrome.
I'll try and share pictures of film on a light table.

Cthulhu fhtagn!

 

[koraks]

I'm pretty hopeless when it comes to blix chemistry, so please correct me if I say something monumentally stupid. But isn't the optimal pH for EDTA and/or PDTA bleaching speed somewhere in the mildly acidic regions? Or is the ~pH6.5 of commercial RA4 blixes a compromise for other reasons, such as arresting development?

 

[The Black Pharaoh]

I have absolutely no access to RA4, but the ph was around 6-7.
I doubt Ra4 blix will work with slide films or even with negative films. I always end up with remaining silver or even iron.

Cinestill negative blix was around the same in my tests.
I do not have access to the reversal blix they offer.

I've tried a few blix recipes in and around 7 Ph.
It's the accelerator that matters. Please correct me if i'm wrong.

I don't know how paper works, but a blix capable of blixing slide film should blix paper no stress right?

My next test will be to skip the PDTA and just use EDTA. Will update.

Cthulhu fhtagn!

 

[koraks]

but the ph was around 6-7.

Oh, alright; I was thrown off by the little bit carbonate, but I suppose this isn't very significant in relation to the EDTA and PDTA.

I doubt Ra4 blix will work with slide films or even with negative films.

Yeah, it won't - or at least not very quickly at all. My remark was more about the chemistry involved - and again, I'm no expert by far in this aread.

I don't know how paper works, but a blix capable of blixing slide film should blix paper no stress right?

Paper is basically silver chloride, but there's not a whole lot of silver in it. Much less so than slide film. Moreover, slide film is a mix of (I think) silver bromide and silver iodide and particularly the latter AFAIK makes blixing a whole lot slower and more challenging. So a blix that's effective for slide film should blix paper without any problem, but the other way around will be problematic.

 

[The Black Pharaoh]

I'm guessing the carbonate is there to dissolve EDTA easily? i can actually get by with some NaOH.

 

[Rudeofus]

Bleaches become stronger at lower pH, so typical commercial bleaches operate somewhere between pH 4 and 5. These bleaches are typically followed up by a neutral fixer at pH 6.5, which makes this neutral fixer the last concentrated liquid to hit the film.

Many dyes are weak acids, and their exact hues are affected by their protonization state, i.e. they have different hue at low pH (with proton) versus high pH (without proton). Since we want well defined color hues, we need to make sure, that the last concentrated bath (which can influence the protonization state of the dyes) has a pH close to 6.5.

In case of BLIX we don't have this fixer bath, therefore the BLIX itself must have pH 6.5. This weakens the already weak ferric EDTA bleach part, but these BLIXes still work, because thiosulfate is a stronger counter anion than bromide.


Regarding @The Black Pharaoh 's BLIX formula: several decades ago Ilford published a patent for ferric EDTA based bleaches. Ilford discovered, that a slight excess of EDTA vs. ferric ion improved bleaching performance. Ilford put this excess at somewhere 5%. Kodak was caught cold by Ilford in this patent, until they made the lucky find, that 1% excess EDTA worked even better than the 5% patented by Ilford.

if you have pure ferric EDTA, some outer electrons of the ferric ion do not bind so well to the EDTA. These incomplete complexes tend to form clusters. These clusters are huge and poorly mobile, which leads to reduced bleach speed. The excess EDTA shifts the balance closer to ferric EDTA or ferric EDTA2 and thereby reduces the problem.

One more factlet: EDTA binds much stronger to ferric ion than PDTA, therefore ferric EDTA bleaches are milder than ferric PDTA bleaches. C-41 materials were at some point tweaked to handle the stronger ferric PDTA bleaches, but E-6 materials never were. Now if you add PDTA instead to EDTA, you may end up with some mixed complexes of ferric ion, EDTA and PDTA, and I would expect these complexes to be stronger oxidizers than ferric EDTA with excess EDTA. This is much less of a problem than all these popular ferricyanide bleaches, but at least you know, that you are somewhat out of spec for E6. C-41 should be fine, though.


Conclusions:

1. I would use Na2-EDTA or EDTA instead of PDTA, and I would reduce the amount to about 0.5g.
2. I would also reduce the Sodium Sulfite content of your BLIX to about 10 g/l. If you add more stuff to oxidizer+fixer, you reduce effectiveness of the bleach (search for "ionic strength")
3. I do like the 0.1g/l Mercaptotriazole, this amount matches my experience
4. If you reduce the 13g PDTA to 0.5g Na2-EDTA, then you can also reduce the amount of Sodium Carbonate in your BLIX.
5. EDTA is a very good buffer through a wide pH range, therefore you can adjust pH with NaOH instead of Na2CO3.
   
   

 

[The Black Pharaoh]

Hi @Rudeofus,

Thank you soo much for your input. I'd very much like to replace PDTA with Na2-EDTA.
Let me try the tweaks you suggested. A milder EDTA blix would be fine with E-6?

Thank you for all the help.

 

[Rudeofus]

As you know, there are two main components in a BLIX: the oxidizer and the fixer part. While the fixer part can do no wrong (except for being too weak and leaving silver ions behind), the oxidizer story is a bit more complicated.

Obviously, if the oxidizer is too weak, you likely won't bleach all the silver. However, if the oxidizer is too strong, other components of your film may become damaged. While I have never heard credible reports of destroyed dyes or gelatin, there are stabilizers in film, which are supposed to prevent Oxygen from attacking the film dyes. These stabilizers are often some sort of reducing agents, that's how you deal with Oxygen. If these stabilizers get oxidized by your bleach, then your film will look just fine - for the first few dozen years, until Oxygen starts taking its toll with your film dyes.

Therefore you have to strike a very careful balance with your oxidizer. It has to oxidize all metallic silver in your film, but it must not attack the stabilizers. E-6 film has been designed to make ferric EDTA work. C-41 works with ferric EDTA, but with its more modern stabilizers can also handle ferric PDTA.

PS: don't throw away your PDTA yet, you can make nice bleach for C-41 with it! I'll post a recipe soon.

 

[dingo_]

Hi @The Black Pharaoh were you able to substitute the PDTA, any update to your tests? where were you able to find the ingredients? searching on artcraftchemicals and can't find some.

 

[psfred]

From what I've gathered over the years, EDTA bleaches work but tend to be very slow compared to DTPA. A small excess of EDTA might fix that issue, I may try it sometime.

Ferricyanide bleaches work very well, but you MUST buffer them to avoid pH related issues with red stains, something that destroyed a large amount of film for me 30+ years ago. Half a gram of borax per 500 mL of ferricyanide bleach works wonders, I use it for C41, ECN-2, and E6. Only real drawback to it is that strong acids contaminating it WILL release hydrogen cyanide, and incomplete washiing WILL precipitate Prussian Blue (ferrocyanide) in both film and fixer.

 

[koraks]

Only real drawback

Do you know if modern C41 and/or ECN2 films employ free radical scavengers that protect the dyes from degradation? If so, a ferricyanide bleach might destroy these, severely affecting the stability of the dyes in storage (also dark storage). This is the reason why a ferricyanide bleach should not be used with RA4 prints. I wonder if a similar problem exists for color film.

 

[Rudeofus]

From what I've gathered over the years, EDTA bleaches work but tend to be very slow compared to DTPA. A small excess of EDTA might fix that issue, I may try it sometime.

A small excess of EDTA is helpful in ferric EDTA based bleaches, and they also need a bleach accelerator. In the same way ferric PDTA bleaches need excess PDTA, but they are strong enough to work without a bleach accelerator. C-41 and ECN-2 can handle ferric PDTA bleaches, but E-6 are not rated for this bleach. @koraks already pointed out, why a stronger than rated bleach may cause trouble later on.

Ferricyanide bleaches work very well, but you MUST buffer them to avoid pH related issues with red stains, something that destroyed a large amount of film for me 30+ years ago. Half a gram of borax per 500 mL of ferricyanide bleach works wonders, I use it for C41, ECN-2, and E6. Only real drawback to it is that strong acids contaminating it WILL release hydrogen cyanide, and incomplete washiing WILL precipitate Prussian Blue (ferrocyanide) in both film and fixer.

ECN-2 is rated for very strong bleaches, so ferricyanide may well work for this process. For C-41 and E-6 please refer to @koraks comment and my note above.

 

[koraks]

ECN-2 is rated for very strong bleaches, so ferricyanide may well work for this process.

Indeed; it's at least indicated by Kodak as an 'official', albeit it 'alternate' bleach. Still, it has left me wondering why this is the case - does ECN2 film involve stabilization/protection mechanisms that survive a ferricyanide bleach? Or is the truth more prosaic: is ECN2 film intended as an intermediate and simply not intended for long-term storage, and does it not even involves the protection that may be present in C41 films, so that whatever bleach you throw at it is inconsequential in the first place? I have very strong suspicions that the latter may be closer to the truth than the former - but admittedly, nothing to back up that suspicion.

 

[Rudeofus]

Indeed; it's at least indicated by Kodak as an 'official', albeit it 'alternate' bleach. Still, it has left me wondering why this is the case - does ECN2 film involve stabilization/protection mechanisms that survive a ferricyanide bleach? Or is the truth more prosaic: is ECN2 film intended as an intermediate and simply not intended for long-term storage, and does it not even involves the protection that may be present in C41 films, so that whatever bleach you throw at it is inconsequential in the first place? I have very strong suspicions that the latter may be closer to the truth than the former - but admittedly, nothing to back up that suspicion.

My impression is, that the movie industry would have gone "you've got to be kidding me, Kodak", if Kodak suddenly mandated extremely gentle bleaches and/or an extra bath. For all I know professional movie makers are much more concerned with archival stability than most folks shooting C-41 a few decades ago, therefore I would expect Vision 500T to be at least as stable as e.g. Kodak Gold 200.

My other impression is, that E-6 film was never really a love child of Kodak: they much preferred the color accuracy of masked C-41 film, and it did not surprise me at all, that they ditched E100VS at the first sign of real trouble. Volumes must have been very low, too, so their motivation to improve the process must have been very close to zero.

 

[koraks]

For all I know professional movie makers are much more concerned with archival stability than most folks shooting C-41 a few decades ago

No doubt, however, the million $ question is whether this extends to the camera originals. I don't know; maybe @Kino or @dokko can comment.

 

[dokko]

No doubt, however, the million $ question is whether this extends to the camera originals. I don't know; maybe @Kino or @dokko can comment.

unfortunately I don't have any information about this, but from a cinematographers point of view the original camera negative (OCN) is pretty much the holy grail and I would be very surprised if the studios would be satisfied with a process which meant their massive investment disintegrating.

in the beginning of digital cameras, film being future proof was often used as an argument as an advantage over digital.

 

[Kino]

No doubt, however, the million $ question is whether this extends to the camera originals. I don't know; maybe @Kino or @dokko can comment.

It's a multi-layered problem with many caveats that depend on budget, producer and copyright owners.

However, as a general rule, the OCN is the Golden Child and precise processing is archival intrinsically.

When you get beyond that initial processing phase, all desires bend to pragmatism (budget).

Historically, all color processes in the Motion Picture Industry are fugitive in nature and the only way to insure longevity is through properly stored Color Separations on B&W stock.

Then budget kicks-in again. It's archival until the budget runs out and the OCN and Separations leave the climate controlled vault and wind up in the producers garage or in a dumpster.

Nothing is forever...

 

[psfred]

The objections to ferricyanide bleach for ECN films is purely environmental, it's somewhat hazardous and in large amounts is a disposal problem. Kodak listed alternatives for it for many years (40 at least), and still lists it as an alternative. I don't know what the current recommendations are, but formaldehyde was required in the final rinse for ECN to stabilize dyes, it was also required in C-41 up to the late 80s as well. I use it on film that has been bleached in ferricyanide since I have it. Hard to get now, again an environmental/health thing.

Cinematography film drove Kodak film production I suspect, probably far more film produced for movies than all the home and hobby use put together. Color negative replaced Technicolor Tripack film in the 60s, only one film to manage and easier to make prints (Technicolor as a company lived on a long time as a processing company I think, so it's hard to tell from credits if a film was Techincolor or color negative, lol).

Reversal film was rarely used for movies after Technicolor became a good alternative, much easier to make and correct prints than it is to duplicate positives.

As far as archival material goes, most of Hollywood production wasn't ever considered art for a long time, just a constant supply of ephemera for the entertainment industry. That is why nitrate stock for negatives hung around for so long, it's cheaper. Release prints have been on "safety film" -- acetate base -- since the 1940s or early 50s, prevents cinema fires. A jammed projector setting 3000 ft of extremely flammable nitrate base on fire was a serious hazard. Quite a few classic films have been lost to warehouse fires or poor storage - once the film stops making money the cost of storing huge amounts of less that stable material pretty much precludes archival storage.

 

[lamerko]

Indeed; it's at least indicated by Kodak as an 'official', albeit it 'alternate' bleach. Still, it has left me wondering why this is the case - does ECN2 film involve stabilization/protection mechanisms that survive a ferricyanide bleach? Or is the truth more prosaic: is ECN2 film intended as an intermediate and simply not intended for long-term storage, and does it not even involves the protection that may be present in C41 films, so that whatever bleach you throw at it is inconsequential in the first place? I have very strong suspicions that the latter may be closer to the truth than the former - but admittedly, nothing to back up that suspicion.

I suspect they designed really stable films in the ECN-2 process.

My other impression is, that E-6 film was never really a love child of Kodak: they much preferred the color accuracy of masked C-41 film, and it did not surprise me at all, that they ditched E100VS at the first sign of real trouble. Volumes must have been very low, too, so their motivation to improve the process must have been very close to zero.

In fact, there seems to be no drama in the VNF-1 and RVNP processes. Why they chose a different approach with E-6 - I don't know...