Chemistry of 7 bath E6 Processing

ChrisGalway · May 3, 2024

Can anyone please point me to a good description of the action/mechanism each step of the traditional E6 chemistry steps? I sort-of understand at a basic level what each step does (the name of each step gives it away!) but I'd like to delve deeper without having to first get a PhD in chemistry. Perhaps there is a good book chapter (or book)?

It's just for curiosity. I've been processing 6 Provia 100f 120 size in the past three days, one at a time in a Paterson tank (all came out great!) and have therefore had a lot of time to realise I should know more about what's going on at each step.

For example, with the Bellini kit I'm using (I like the results), the only water wash is between the 1st Developer and the Reversal bath, and the final wash between the Fixer and the Stabiliser ... no washes in between. Bellini confirmed this when I asked them ... but what's the reason/logic for no washes? I'd like to understand what I'm doing, rather than merely following instructions.

I'm also curious to know which are the most toxic of the 7 baths (I'm including the stabiliser here), and which are relatively innocuous.

koraks · May 3, 2024

ChrisGalway said:
what's the reason/logic for no washes?

In some cases because you can get away with no washes.
In some cases because an intermediate wash can actually be a problem; the only thing that comes to mind is the pre-bleach to bleach transition, which can render the pre-bleach ineffective if you wash in-between these steps. With the other steps, it's usually possible to wash in-between, although not absolutely necessary as you've noticed.

ChrisGalway said:
which are the most toxic of the 7 baths (I'm including the stabiliser here)

Depends on the chemistry and also on how you define 'toxic'. It makes a difference whether you want to assess the impact of accidental swallowing (kid or pet drinking from one of your chemistry bottles) vs. the exposure to you as a (responsible) user. And even whether the chemistry is unused or used; e.g. fixer will be fairly innocuous when fresh, but as soon as it's used, it has silver salts dissolved in it which are more harmful to life forms. Which brings me to one more remark: it depends also on what organism(s) or biological systems you want to assess the impact of. Human toxicity is a different matter from aquatic life. And of course, this also (you guessed it already) depends on how the chemistry is used and in particular how it's disposed of.

As to reading, I'd start here: https://en.wikipedia.org/wiki/E-6_process
It's actually pretty good, quite clear and yet fairly comprehensive.

ChrisGalway · May 3, 2024

koraks said:
In some cases because you can get away with no washes.
In some cases because an intermediate wash can actually be a problem; the only thing that comes to mind is the pre-bleach to bleach transition, which can render the pre-bleach ineffective if you wash in-between these steps. With the other steps, it's usually possible to wash in-between, although not absolutely necessary as you've noticed.

Depends on the chemistry and also on how you define 'toxic'. It makes a difference whether you want to assess the impact of accidental swallowing (kid or pet drinking from one of your chemistry bottles) vs. the exposure to you as a (responsible) user. And even whether the chemistry is unused or used; e.g. fixer will be fairly innocuous when fresh, but as soon as it's used, it has silver salts dissolved in it which are more harmful to life forms. Which brings me to one more remark: it depends also on what organism(s) or biological systems you want to assess the impact of. Human toxicity is a different matter from aquatic life. And of course, this also (you guessed it already) depends on how the chemistry is used and in particular how it's disposed of.

As to reading, I'd start here: https://en.wikipedia.org/wiki/E-6_process
It's actually pretty good, quite clear and yet fairly comprehensive.

Thanks Koraks, much appreciated!

I'm aware of the E6 wiki page ... I wanted something beyond ... that if it exists. I did a 3 year Photographic Technology Diploma course 50 years ago but have forgotten much of it.

Regarding "toxic", I'm thinking of disposal. I can't imagine our local council accepting 7 different solutions, not knowing what's in them. My gut feeling is the the used fixer is the worst for the environment. But surely some of the baths are less harmful. After all, many people use a dishwasher every single day with horrible cleaning chemicals, they run their washing machine several times a week with equally nasty stuff (the television adverts give warnings), not to mention pouring household bleach down the drain for all kinds of purposes. I'm trying to get a handle on how bad small quantities of E6 chemicals (30 films a year) really are relative to the daily use of others. We have to be realistic and follow the science.

Rudeofus · May 3, 2024

ChrisGalway said:
I'm aware of the E6 wiki page ... I wanted something beyond ... that if it exists. I did a 3 year Photographic Technology Diploma course 50 years ago but have forgotten much of it.

There is a great chapter about color processes in part 2 of Grant Haist's opus "Modern Photographic Processing". In this chapter you'll find anything you ever wanted to know about reversal processing and then some. Sadly the book is out of print, but used copies may still be available.

ChrisGalway said:
Regarding "toxic", I'm thinking of disposal. I can't imagine our local council accepting 7 different solutions, not knowing what's in them. My gut feeling is the the used fixer is the worst for the environment. But surely some of the baths are less harmful. After all, many people use a dishwasher every single day with horrible cleaning chemicals, they run their washing machine several times a week with equally nasty stuff (the television adverts give warnings), not to mention pouring household bleach down the drain for all kinds of purposes. I'm trying to get a handle on how bad small quantities of E6 chemicals (30 films a year) really are relative to the daily use of others. We have to be realistic and follow the science.

In my home country (EU member in Central Europe) disposal of chemistry is quite simple: they want me to separate "stuff with silver" from "stuff without much silver" and accept amateur quantities of photo chemistry for free, which means in practice: 5l canisters are good, 10l canisters may be still ok sometimes, 25l canisters are not good. Showing up every other week with that amount is also ok.

Our hazmat place takes the "stuff without much silver" and neutralizes it, then dumps it in the sewer. They take the "stuff with silver", extract the silver and process the rest like "stuff without much silver". As a matter of fact photo chemistry in small to moderate quantities is not seen as particularly toxic or harmful to the environment, the main issue could stem from excessive alkalinity or acidity, which is taken care of as described.

Therefore at 30 rolls/year I would not expect that you have to jump through burning hoops to lawfully dispose of your used chems. The likely ingredients of E-6 7 bath process can be found in Kodak's e-6 5 liter kit teaching patent, which I unwrapped in a series of short articles here on photrio. You can use these formulas to mix your own, but I doubt you'll need them to facilitate disposal of old chems.

mshchem · May 3, 2024

Kodak Technical Documents • 125px

Look at Z-119

cmacd123 · May 4, 2024

or if you want the Philosophy read C. E. Kenneth Mees Book,

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961

Item no longer available

The item you are looking for is no longer available.

www.abebooks.com

that of course was written before the E6 process.
all depends on how much you want to learn.

mshchem · May 4, 2024

cmacd123 said:
or if you want the Philosophy read C. E. Kenneth Mees Book,

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961

Item no longer available

The item you are looking for is no longer available.

www.abebooks.com

that of course was written before the E6 process.
all depends on how much you want to learn.

This is an amazing book. It covers a fascinating bit of history.

Samu · May 5, 2024

koraks said:
In some cases because you can get away with no washes.
In some cases because an intermediate wash can actually be a problem; the only thing that comes to mind is the pre-bleach to bleach transition, which can render the pre-bleach ineffective if you wash in-between these steps. With the other steps, it's usually possible to wash in-between, although not absolutely necessary as you've noticed.

Depends on the chemistry and also on how you define 'toxic'. It makes a difference whether you want to assess the impact of accidental swallowing (kid or pet drinking from one of your chemistry bottles) vs. the exposure to you as a (responsible) user. And even whether the chemistry is unused or used; e.g. fixer will be fairly innocuous when fresh, but as soon as it's used, it has silver salts dissolved in it which are more harmful to life forms. Which brings me to one more remark: it depends also on what organism(s) or biological systems you want to assess the impact of. Human toxicity is a different matter from aquatic life. And of course, this also (you guessed it already) depends on how the chemistry is used and in particular how it's disposed of.

As to reading, I'd start here: https://en.wikipedia.org/wiki/E-6_process
It's actually pretty good, quite clear and yet fairly comprehensive.

Also chemical reversal in E6 will work only when the alkaline color developer will hit the film. The stannous chloride in reversal bath is in slightly acidic solution which is by itself ineffective. This is actually a built in problem with E6 in replenished systems, because the pH of the color developer is prone to get too low because of the carryover of reversal bath. This needs to be monitored and often it is necessary to correct the pH by adding sodium hydroxide. This is a problem because in E6 process, the wrong pH of the color developer will easily lead to issues in color balance. If you wash in between the reversal bath and color developer the film will be ruined.

Samu · May 5, 2024

mshchem said:
Kodak Technical Documents • 125px

Look at Z-119

Or Fuji TB for Pro6. It has also some good information. There is also an old manual published by Jobo, which can be found in the interner at mr-alvandi.com. Kodak Z-119 is probably still the best resource.

ChrisGalway · May 6, 2024

Thanks all! Your information, plus the Kodak, Fuji and Jobo documents make me much more aware of the E6 process. The books and book-chapters look excellent but are either unaffordable or not available at present.

So when I'm processing my batches of 6-8 Provia 100f 120 size films, one by one in a Paterson tank, say about an hour in all, I can now be thinking of what those 6/7 baths are actually doing. The reward of removing the film from the reel at the end and seeing those jewels makes it worth it!

psfred · May 11, 2024

In a nutshell, this is what happens: the first developer is a black and white developer that produces a negative image of whatever the film was exposed to. Since E6 films are "substantive" films (meaning the dye couplers are in the film, not the developing solutions) the sliver negative image effectively removes the negative image from the color development step. Time and temperature determine how dense this negative image is, which is why you can "pull" or "push" the film at this step to get more or less development.

Stop bath prevents further development of the negative image and removes the black and white developer from the film so it won't interfere with color development.

Reversal bath chemically "exposes" the remaining silver halide not converted to silver in the first developer so that the color developer will work on it. You can skip this step and simply expose the film to bright artificial light after washing the stop bath out completely. In the E4 process, there was no reversal bath, the color developer contained tetra-butyl amine-borane which did the reversal, but it's a strong carcinogen and toxic -- the only other use for it that I know of was "zip fuel" for added thrust in jet engines, and it caused trouble there too.

Color development actually produces the color dyes in the film to give a color image. The developer molecule is oxidized by the chemical reaction of reducing sliver bromide/iodide to metallic sliver, and at high pH the oxidized color developer chemical reacts with non-colored dye couplers embedded in tiny resin beads in the gelatin coatings of the film to produce the appropriate color dye for each layer. Color developer is pretty strong, and will develop all of the remaining silver halide in the film, producing dyes. The ratio of blue to yellow in Ekatchrome films or green to magenta in Fuji films is a function of the actual pH of the developer, which is why in time past processors would dedicate different machines to Kodak or Fuji film -- when one was correct, the other would be off enough to notice.

The bleach step coverts all the metallic silver produced in the development steps back to sliver halides (usually bromide), and the fixing step removes the sliver halides from the film.

The stabilizer step acts to prevent age related dye formation or changes, although modern films no longer require formalidehyde to "fix" cyan dye couplers that would in the past discolor with time

Modern bleaches do not react with fixer, so here is no need to wash them out between bleach and fix. Older chemistries, particularly ferricyanide bleach, must be washed out or ferrocyanide (Prussian blue) will precipitate in the film and cause trouble Chelated iron bleaches do not cause this problem, and in some developer kits are combined with the fixer anyway to make "Blix" that both bleaches and fixes the film.

ChrisGalway · May 11, 2024

psfred said:
In a nutshell, this is what happens: the first developer is a black and white developer that produces a negative image of whatever the film was exposed to. Since E6 films are "substantive" films (meaning the dye couplers are in the film, not the developing solutions) the sliver negative image effectively removes the negative image from the color development step. Time and temperature determine how dense this negative image is, which is why you can "pull" or "push" the film at this step to get more or less development.

Stop bath prevents further development of the negative image and removes the black and white developer from the film so it won't interfere with color development.

Reversal bath chemically "exposes" the remaining silver halide not converted to silver in the first developer so that the color developer will work on it. You can skip this step and simply expose the film to bright artificial light after washing the stop bath out completely. In the E4 process, there was no reversal bath, the color developer contained tetra-butyl amine-borane which did the reversal, but it's a strong carcinogen and toxic -- the only other use for it that I know of was "zip fuel" for added thrust in jet engines, and it caused trouble there too.

Color development actually produces the color dyes in the film to give a color image. The developer molecule is oxidized by the chemical reaction of reducing sliver bromide/iodide to metallic sliver, and at high pH the oxidized color developer chemical reacts with non-colored dye couplers embedded in tiny resin beads in the gelatin coatings of the film to produce the appropriate color dye for each layer. Color developer is pretty strong, and will develop all of the remaining silver halide in the film, producing dyes. The ratio of blue to yellow in Ekatchrome films or green to magenta in Fuji films is a function of the actual pH of the developer, which is why in time past processors would dedicate different machines to Kodak or Fuji film -- when one was correct, the other would be off enough to notice.

The bleach step coverts all the metallic silver produced in the development steps back to sliver halides (usually bromide), and the fixing step removes the sliver halides from the film.

The stabilizer step acts to prevent age related dye formation or changes, although modern films no longer require formalidehyde to "fix" cyan dye couplers that would in the past discolor with time

Modern bleaches do not react with fixer, so here is no need to wash them out between bleach and fix. Older chemistries, particularly ferricyanide bleach, must be washed out or ferrocyanide (Prussian blue) will precipitate in the film and cause trouble Chelated iron bleaches do not cause this problem, and in some developer kits are combined with the fixer anyway to make "Blix" that both bleaches and fixes the film.

Thanks for this detail. I'm definitely more informed now after all the above responses. Processing two more rolls of Provia 100f today ...

Nehalem501 · May 12, 2024

psfred said:
The stabilizer step acts to prevent age related dye formation or changes, although modern films no longer require formalidehyde to "fix" cyan dye couplers that would in the past discolor with time

That's true for C-41 / ECN-2 films, but not E-6. Chrome films still need the formaldehyde, it's just that the process changed with formaldehyde being in a different form in the pre-bleach bath instead of the stabilizer bath (see the various posts from PE on the subjects).

Rudeofus · May 12, 2024

The switch from "C-41 needs Formaldehyde" to "C-41 doesn't need Formaldehyde" also happened much later, according to PE around 2000. He posted this in a sticky thread here, which should once and for all settle this case.

Samu · May 15, 2024

psfred said:
In a nutshell, this is what happens: the first developer is a black and white developer that produces a negative image of whatever the film was exposed to. Since E6 films are "substantive" films (meaning the dye couplers are in the film, not the developing solutions) the sliver negative image effectively removes the negative image from the color development step. Time and temperature determine how dense this negative image is, which is why you can "pull" or "push" the film at this step to get more or less development.

Stop bath prevents further development of the negative image and removes the black and white developer from the film so it won't interfere with color development.

Reversal bath chemically "exposes" the remaining silver halide not converted to silver in the first developer so that the color developer will work on it. You can skip this step and simply expose the film to bright artificial light after washing the stop bath out completely. In the E4 process, there was no reversal bath, the color developer contained tetra-butyl amine-borane which did the reversal, but it's a strong carcinogen and toxic -- the only other use for it that I know of was "zip fuel" for added thrust in jet engines, and it caused trouble there too.

Color development actually produces the color dyes in the film to give a color image. The developer molecule is oxidized by the chemical reaction of reducing sliver bromide/iodide to metallic sliver, and at high pH the oxidized color developer chemical reacts with non-colored dye couplers embedded in tiny resin beads in the gelatin coatings of the film to produce the appropriate color dye for each layer. Color developer is pretty strong, and will develop all of the remaining silver halide in the film, producing dyes. The ratio of blue to yellow in Ekatchrome films or green to magenta in Fuji films is a function of the actual pH of the developer, which is why in time past processors would dedicate different machines to Kodak or Fuji film -- when one was correct, the other would be off enough to notice.

The bleach step coverts all the metallic silver produced in the development steps back to sliver halides (usually bromide), and the fixing step removes the sliver halides from the film.

The stabilizer step acts to prevent age related dye formation or changes, although modern films no longer require formalidehyde to "fix" cyan dye couplers that would in the past discolor with time

Modern bleaches do not react with fixer, so here is no need to wash them out between bleach and fix. Older chemistries, particularly ferricyanide bleach, must be washed out or ferrocyanide (Prussian blue) will precipitate in the film and cause trouble Chelated iron bleaches do not cause this problem, and in some developer kits are combined with the fixer anyway to make "Blix" that both bleaches and fixes the film.

Modern E6 has no stop bath, but a wash with water after 1st developer. Early versions had this, but the modern version had the strength of the 1st developer slightly altered to compensate with water wash not immediately stopping the process as an acid bath would do.
For reversal, E6 uses stannous chloride in slightly acidic solution, and the reversal will take place when it reacts with the alkaline color developer. Exposing to light would also be possible, but taking wet film off the reels and respooling it when wet is quite risky for damaging the film. I don't know hoe this is made in "Tetena; style" home kits combining steps, or which chemical is used for reversal.

What you say about stabilizing, is correct for C-41, but not for E-6. Instead of formalin based final rinse though, this is done in modern version of the process by conditioner (or with modern name, pre bleach). It will cause formation of formaldehyde in film when the pre bleach is carried over to the bleach. Tetenal made home kits had a formalin based stabilizer, but some of the cheaper home kits omit stabilizing or conditioning altogether. This is a problem with longevity of dyes.. The wash step between bleach and fix is optional, but Fuji recommends it in some commercial settings when output is low.

koraks · May 16, 2024

Samu said:
I don't know hoe this is made in "Tetena; style" home kits combining steps, or which chemical is used for reversal.

I think you're supposed to expose the film while still on the reel. How well this works, depends on the reel, I guess. But I think this is also why relatively long fogging exposures are prescribed - to give the shaded bits of the film a chance to fog.

Rudeofus · May 16, 2024

Samu said:
I don't know hoe this is made in "Tetena; style" home kits combining steps, or which chemical is used for reversal.

There is a compound of the "you don't want this near you in concentrated form" and "you won't be able to buy this compound as an amateur" type called Tertiary Butylamine Borane also known as "Kodak Reversal Agent 1". This is a compound, which both fogs film very well, and which is compatible with the very alkaline environment of E-6 CD.

AFAIK Tetenal has this compound in one of their E-6 CD component concentrates.

Samu · May 16, 2024

Rudeofus said:
There is a compound of the "you don't want this near you in concentrated form" and "you won't be able to buy this compound as an amateur" type called Tertiary Butylamine Borane also known as "Kodak Reversal Agent 1". This is a compound, which both fogs film very well, and which is compatible with the very alkaline environment of E-6 CD.

AFAIK Tetenal has this compound in one of their E-6 CD component concentrates.

Thanks. I am much more familiar with the standard 6-bath process.

Samu · May 16, 2024

koraks said:
I think you're supposed to expose the film while still on the reel. How well this works, depends on the reel, I guess. But I think this is also why relatively long fogging exposures are prescribed - to give the shaded bits of the film a chance to fog.

Maybe this is quite irrelevant, as chemical fogging works fine in most cases. I have been looking the different procedures used for black & white reversal, and there is no one way people do the exposure. Some suggest doing it just on the reel, some in water on reel, but others insist that the film must be taken out of the spool and respooled for good results. I have no experience of this process, and don´t have an opinion what is right. I have done quite a lot of E6, mostly with standard chemistry, but have also tried some of the 3-bath kits - years ago, and only those made by Tetenal. I have never done reversal by exposure to light, although I know it is an option. I have to try it just for curiosity.

koraks · May 17, 2024

I did an "on the reel" fogging exposure a week or two ago in a different context; this was as part of chromium intensifier, which for some reason seems to work better (or at all) if strong UV exposure is given to the film after the bleach bath. It worked fine, but I did take a minute or two to carefully rotate the reel along 3 axes underneath the UV source.

For a reversal process, I'd always opt for chemical fogging if it's possible in any way, really.

MingMingPhoto · Jul 14, 2024

Samu said:
Modern E6 has no stop bath, but a wash with water after 1st developer. Early versions had this, but the modern version had the strength of the 1st developer slightly altered to compensate with water wash not immediately stopping the process as an acid bath would do.
For reversal, E6 uses stannous chloride in slightly acidic solution, and the reversal will take place when it reacts with the alkaline color developer. Exposing to light would also be possible, but taking wet film off the reels and respooling it when wet is quite risky for damaging the film. I don't know hoe this is made in "Tetena; style" home kits combining steps, or which chemical is used for reversal.

What you say about stabilizing, is correct for C-41, but not for E-6. Instead of formalin based final rinse though, this is done in modern version of the process by conditioner (or with modern name, pre bleach). It will cause formation of formaldehyde in film when the pre bleach is carried over to the bleach. Tetenal made home kits had a formalin based stabilizer, but some of the cheaper home kits omit stabilizing or conditioning altogether. This is a problem with longevity of dyes.. The wash step between bleach and fix is optional, but Fuji recommends it in some commercial settings when output is low.

hi samu, do you have any idea how I can mix my own stabilizer? I'm runnign a small operation and we use the tetenal kits to process peoples film. I've had to switch to arista but it does not contain a stabilizer. do you think a stablizer is necessary? or is using photo flo fine? If it's not goot then how can I mix my own stalizer?

Samu · Jul 14, 2024

MingMingPhoto said:
hi samu, do you have any idea how I can mix my own stabilizer? I'm runnign a small operation and we use the tetenal kits to process peoples film. I've had to switch to arista but it does not contain a stabilizer. do you think a stablizer is necessary? or is using photo flo fine? If it's not goot then how can I mix my own stalizer?

Tetejal is bankrupt for about a year or so now. I doubt those kits are sold anywhere. Basically. the stabilizer they used is formalin and surfactant similar to Photo-Flo. For derails, read this sticky by PE in this forum. https://www.photrio.com/forum/threads/the-definitive-word-i-hope-on-color-stabilzers.89149/

MingMingPhoto · Jul 14, 2024

thank you!

ChrisGalway · Jul 15, 2024

Adox are "reviving" the Tetenal chemistry, and have announced both C-41 and E6 1-litre kits. These are advertised at their retail outlet FotoImpex and the C-41 kit at Freestyle in the US. I suspect the C-41 will be available in 1-2 months (the hold ups are related to packaging) and I'm sure the E6 will be available later this year. My understanding is that these kits are "the same" as the Tetenal ones. I've been using the Bellini 6-bath (+stabiliser) kits since Tetenal went belly-up, and I'm very happy with them. 6-bath sounds difficult compared to 3-bath, but there are no washes between most steps, so actually it's not much more difficult or lengthy. And many people claim the 6-bath process (the original) is somehow "better" than the 3-bath compromise kits.

Chemistry of 7 bath E6 Processing

ChrisGalway

koraks

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ChrisGalway

Rudeofus

mshchem

cmacd123

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961

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mshchem

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961

Item no longer available

Samu

Samu

ChrisGalway

psfred

ChrisGalway

Nehalem501

Rudeofus

Samu

koraks

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Rudeofus

Samu

Samu

koraks

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MingMingPhoto

Samu

MingMingPhoto

ChrisGalway

Chemistry of 7 bath E6 Processing

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From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961 ​

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961 ​

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Privacy & Transparency

Privacy & Transparency

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961

From dry plates to Ektachrome film;: A story of photographic research Hardcover – January 1, 1961