Fogging Developer for Reversal

relistan · Jan 10, 2021

I have been doing a lot of reversal testing in the other thread on peroxide bleaches. Along the way I decided to try a fogging developer to make the second part of the process less annoying: expose, redevelop, wash, fix could theoretically be replaced with redevelop, wash. I looked into getting Iron Out which is available in the US and is often used for this by photo hobbyists because it's got quite a lot of sodium dithionite. It seems to be spottily available in Europe, but I can't find anyone who will ship it here. The usual suspects for photo stuff don't seem to sell it as a raw chemical. So I started looking for other products based on dithionite. I found two and was able to get my hands on one.

The products I found that seem reasonably available in Europe are:

Dr. Beckmann's Color Run Remover — https://www.dr-beckmann.co.uk/product/colour-run-remover/
Dylon Pre Dye — https://www.dylon.co.uk/en/home/products/pre-dye.html

I needed to order something that was available in Ireland due to the Brexit mess here right now and the pandemic (can't order from UK effectively, and Europe is super slow). So I got the Dylon Pre Dye. I exposed a film leader to sunlight and developed it in there for awhile. I didn't pay much attention to concentration or time, just wanted to see if it worked at all. Well, it does.

I got a fully darkened section of film. It does, however, have a bit of a brown cast. Not sure about the cause of that. While it's not ideal to have to fix it, I will try that and see if it effects the brown cast.

Anyway, it was an experiment and thought I'd share it. If people know of a nicer or better way to do it, please let me know. Other folks seem to know better ways to find stuff over here.

YoIaMoNwater · Jan 10, 2021

Chemical fogging agents are interesting. I wonder if anyone has information on the mechanism in how they work.

The only stuff I tried was stannous chloride (suggested in Jens Osbahr's protocol) that I managed to find in my lab and that stuff was super super expired, like more than 2 decades expired. I tried to add into Microphen when I first got into reversal processing but it wouldn't dissolve completely, so I had to filter the fogging developer. In the end my first and only attempt using a second fogging developer led to a mixture of positive and negative images, which I figured out was due to incomplete bleaching.

As for the brown cast in your attempt, I'm not really sure what it is. Honestly, I don't mind physically taking the reel out of the tank and re-exposing them to light. I follow what this guy does with a bowl of water ( at around 7 min mark) and expose each side of the reel for 1.5 min under two 50W lamps.

Raghu Kuvempunagar · Jan 10, 2021

relistan said:
got a fully darkened section of film. It does, however, have a bit of a brown cast

What are the ingredients of this dye remover other than dithionite? And did you add carbonate to it?

Rudeofus · Jan 11, 2021

YoIaMoNwater said:
Chemical fogging agents are interesting. I wonder if anyone has information on the mechanism in how they work.

The only stuff I tried was stannous chloride (suggested in Jens Osbahr's protocol) that I managed to find in my lab and that stuff was super super expired, like more than 2 decades expired. I tried to add into Microphen when I first got into reversal processing but it wouldn't dissolve completely, so I had to filter the fogging developer.

Fogging agents are typically dilute, strong reducers. They create tiny specks of developed silver on the surface of silver halide grains, just what exposure usually does, and the silver halide grains become developable. If the reducer is sufficiently concentrated, such as in these rust remover bathes, whole silver halide grains will be developed.

The reason why your sample of Stannous Chloride didn't dissolve is formation of Stannous Hydroxide, which is insoluble. Stannous Chloride is soluble as long as you keep it either acidic, or tied in a complex such as ATMP. It will also complex with Citric Acid, but I don't know how long it will remain active (see Fenton reaction). This is one of the risks of Stannous Chloride: it will be a powerful fogging agent even in very weak solution, but at some point it will just stop working and you get irrecoverable blank slides.

Here is what I recommend as fogging bath, assuming that powerful sequestering agents are out of reach:

Mix 20g/l Citric Acid with 0.5 g/l Stannous Chloride and use this within a few hours
Alternatively I have seen the recommendation "1 tea spoon of Sodium Dithionite in one liter of water" used single shot. Use one of the various rust removers as long as they don't contain stuff which kills you or your film roll.

Raghu Kuvempunagar · Jan 11, 2021

Rudeofus said:
Alternatively I have seen the recommendation "1 tea spoon of Sodium Dithionite in one liter of water" used single shot.

With 1 TSP of sodium carbonate.

Rudeofus · Jan 11, 2021

relistan said:
The usual suspects for photo stuff don't seem to sell it as a raw chemical. So I started looking for other products based on dithionite. I found two and was able to get my hands on one.

The products I found that seem reasonably available in Europe are:

Dr. Beckmann's Color Run Remover — https://www.dr-beckmann.co.uk/product/colour-run-remover/

Dylon Pre Dye — https://www.dylon.co.uk/en/home/products/pre-dye.html

While looking for details about this "Dylon Pre-Dye" product, I ran into a German outlet carrying the raw ingredient. Maybe you can even get this somewhere locally in Ireland?

@Raghu Kuvempunagar : yes, if you add Sodium Carbonate or Sodium Hydroxide to Sodium Dithionite, it will be less smelly. If is beneficial, but AFAIK not absolutely required.

Raghu Kuvempunagar · Jan 11, 2021

Rudeofus said:
@Raghu Kuvempunagar : yes, if you add Sodium Carbonate or Sodium Hydroxide to Sodium Dithionite, it will be less smelly. If is beneficial, but AFAIK not absolutely required.

Sodium carbonate is added to provide an alkalinity of pH10-11 which is optimal for dithionite's stability in aqueous solution. Dithionite deteriorates rapidly in pH < 9 and > 11.5 and the deterioration products such as thiosulphate can have non-trivial influence on the results you get. Even the alkaline dithionite solution is best used with one hour of mixing.

relistan · Jan 11, 2021

YoIaMoNwater said:
As for the brown cast in your attempt, I'm not really sure what it is. Honestly, I don't mind physically taking the reel out of the tank and re-exposing them to light. I follow what this guy does with a bowl of water ( at around 7 min mark) and expose each side of the reel for 1.5 min under two 50W lamps.

Thanks! Yeah, I don't mind taking the film out to expose it, but it's a bunch more steps than if I can get dithionite working, because it works in place of re-exposure, 2nd developer, and fixer. It will save a lot of time if I do this more often.

Raghu Kuvempunagar said:
What are the ingredients of this dye remover other than dithionite? And did you add carbonate to it?

I had been unable to find an MSDS for it and so I wrote to them this weekend asking for it. I got this this morning. It turns out that it has sodium carbonate already in it. Here are the only items on the MSDS:

That's less dithionite than I would have expected. Iron Out contains 15-40%.

Rudeofus said:
Fogging agents are typically dilute, strong reducers. ...

Thanks! As usual your explanation is super good and helps a lot.

Rudeofus said:
While looking for details about this "Dylon Pre-Dye" product, I ran into a German outlet carrying the raw ingredient. Maybe you can even get this somewhere locally in Ireland?

Ah, very interesting! I did not find that while searching. I did find Jacquard products, but not the bare hydrosulfite/dithionite. They have a similar "color remover" product that I had seen.

I had found this in Ireland: https://appleoakfibreworks.com/coll...s/hydros-oxygen-remover?variant=9181727916089 but it's quite expensive in comparison to the Dylon product, so I am still hoping that might work. Now that I see how low the dithionite content is for the Dylon Pre-Dye, I am unsure if it will work. That Patin-A site seems to be the only one in Europe (in a few pages of Google results) that has it. Shipping doubles the price so that stuff in Ireland looks less expensive in the end. It seems that fabric dye people call it "Hydro" or "Hydros" so I'll have a go at searching for that.

grainyvision · Jan 11, 2021

Very interesting that you found a product with carbonate and dithionite. Raising the pH is what I'd recommend to reduce the brown cast and increase overall speed. Note that dithionite will naturally decay to metabisulfite even as a powder in a process that's near impossible to prevent. (there's some patents to keep dithionite stable at freezing temperatures for "up to 1 week", but that's it). Luckily dithionite in excess doesn't have any ill effects though, but carbonate in a second developer might (excessive swelling). Also the dithionite being stored along with carbonate and not metabisulfite might make it's keeping properties as a solution worse, meaning you might only have 5% or less in this product.

There's been very little research I could find about second developers using dithionite, likely due to these troublesome keeping properties. Regardless, I've done some research. Dithionite will primarily behave as a fogging agent at acidic pH and will behave as both a fogging and developing agent at neutral to alkali pH. I imagine if you increase the pH to a workable level (say balanced between 9 and 11 using baking soda and carbonate), you could introduce a superadditive developer, such as phenidone. The ultimate solution of course is to use a 2 bath second developer. First the dithionite solution at neutral pH which will fog the film faster than develop it. And then using a paper developer to get a neutral tone once it is fogged. I believe that the brown tone from dithionite may be due to surface-only development, which indicates another agent used in conjunction could do the chemical style development which would eliminate this effect, or maybe even just a very small amount of silver solvent such as thiocyanate or thiosulfate to allow dithionite to penetrate the grains

YoIaMoNwater · Jan 11, 2021

Rudeofus said:
Fogging agents are typically dilute, strong reducers. They create tiny specks of developed silver on the surface of silver halide grains, just what exposure usually does, and the silver halide grains become developable. If the reducer is sufficiently concentrated, such as in these rust remover bathes, whole silver halide grains will be developed.

The reason why your sample of Stannous Chloride didn't dissolve is formation of Stannous Hydroxide, which is insoluble. Stannous Chloride is soluble as long as you keep it either acidic, or tied in a complex such as ATMP. It will also complex with Citric Acid, but I don't know how long it will remain active (see Fenton reaction). This is one of the risks of Stannous Chloride: it will be a powerful fogging agent even in very weak solution, but at some point it will just stop working and you get irrecoverable blank slides.

Here is what I recommend as fogging bath, assuming that powerful sequestering agents are out of reach:

Mix 20g/l Citric Acid with 0.5 g/l Stannous Chloride and use this within a few hours

Alternatively I have seen the recommendation "1 tea spoon of Sodium Dithionite in one liter of water" used single shot. Use one of the various rust removers as long as they don't contain stuff which kills you or your film roll.

Interesting. So would DTT also work since it's a reducing agent? I know for DTT it goes bad in matter of days so it should be used as soon as possible. Alternatively we have TCEP in our lab (very very expensive stuff but very stable) that function the same as DTT as a reducing agent. Your explanation on why stannous chloride doesn't dissolve makes sense, although I only used it once since it is a toxic heavy metal, the fact that it's pH dependent on its solubility will be an issue in film developers (as far as I know most developers are above pH 7). DTT and TCEP themselves don't have this issue since I have used them in protein purification where the optimal pH is 7.5.

Edit: Seems like I answered my own questions. Here's a list of reducing agent commonly used in molecular biology: https://www.ebi.ac.uk/chebi/searchId.do?chebiId=63247

I suppose their chemical function could also be applied for photography.

And here's a short and good explanation of what TCEP is: https://www.goldbio.com/articles/article/TCEP-the-Reducing-Agent

Rudeofus · Jan 11, 2021

The aim of most fogging agents is to make silver halide grains developable, but not to develop them in quantity. This is especially a concern in color processing. If you look at this list on ebi.ac.uk, there are

strong silver solvents like thioglycolate and thiosulfate
well known photographic developers like ascorbate or ferrous sulfate, which will not reduce unexposed silver halide
compounds which create extremely insoluble silver salts like Sodium Selenide, or are insoluble by themselves like metallic Tin or Pyrite
compounds known to not develop silver like Sodium Sulfite

As you can see, once you purge the list from no goes, not much remains.

PS: The phrase "Researchers often add TCEP to denature proteins during preparation of protein samples" should be interpreted as "god knows what it does to gelatin".

Rudeofus · Jan 11, 2021

relistan said:
I had found this in Ireland: https://appleoakfibreworks.com/coll...s/hydros-oxygen-remover?variant=9181727916089 but it's quite expensive in comparison to the Dylon product, so I am still hoping that might work. Now that I see how low the dithionite content is for the Dylon Pre-Dye, I am unsure if it will work. That Patin-A site seems to be the only one in Europe (in a few pages of Google results) that has it. Shipping doubles the price so that stuff in Ireland looks less expensive in the end. It seems that fabric dye people call it "Hydro" or "Hydros" so I'll have a go at searching for that.

In my experience chemistry is expensive to ship, especially to other countries, therefore it may be the cheapest to source the dithionite locally. 100 grams will develop quite a bit of film. You may even talk them into selling the raw compound instead of packaged stuff.

relistan · Jan 11, 2021

earlz said:
Very interesting that you found a product with carbonate and dithionite. Raising the pH is what I'd recommend to reduce the brown cast and increase overall speed. Note that dithionite will naturally decay to metabisulfite even as a powder in a process that's near impossible to prevent. (there's some patents to keep dithionite stable at freezing temperatures for "up to 1 week", but that's it). Luckily dithionite in excess doesn't have any ill effects though, but carbonate in a second developer might (excessive swelling). Also the dithionite being stored along with carbonate and not metabisulfite might make it's keeping properties as a solution worse, meaning you might only have 5% or less in this product.

This is really good info. The product is a powder rather than a liquid, probably for the reasons you describe. It's meant to be used in one batch, which means there is every possibility that the dithionite is not evenly mixed with the carbonate. It's not powder, though, and it doesn't look like the sodium carbonate crystals that I have. It's sort of uneven, very small chunks. Possibly both carbonate and dithionite crystallized together? I don't even know if that's possible. I used a really small amount for the test on a small cut of film, maybe not enough to get the pH up high enough. I'll use some pH paper to figure out what the pH is next time.

earlz said:
There's been very little research I could find about second developers using dithionite, likely due to these troublesome keeping properties. Regardless, I've done some research. Dithionite will primarily behave as a fogging agent at acidic pH and will behave as both a fogging and developing agent at neutral to alkali pH. I imagine if you increase the pH to a workable level (say balanced between 9 and 11 using baking soda and carbonate), you could introduce a superadditive developer, such as phenidone. The ultimate solution of course is to use a 2 bath second developer. First the dithionite solution at neutral pH which will fog the film faster than develop it. And then using a paper developer to get a neutral tone once it is fogged. I believe that the brown tone from dithionite may be due to surface-only development, which indicates another agent used in conjunction could do the chemical style development which would eliminate this effect, or maybe even just a very small amount of silver solvent such as thiocyanate or thiosulfate to allow dithionite to penetrate the grains

Very interesting that phenidone is superadditive with it. I have phenidone. I have also been using paper developer as my second developer. Interesting set of possibilities there to look at down the road. Thanks!

The idea that the brown tone is from surface development makes a lot of sense! In further experiments I'll pay attention to the pH, concentration, etc now that I know it works. If I get a good result, great. If not, I have sodium thiosulfate on hand and could try a small amount of that.

relistan · Jan 11, 2021

Rudeofus said:
In my experience chemistry is expensive to ship, especially to other countries, therefore it may be the cheapest to source the dithionite locally. 100 grams will develop quite a bit of film. You may even talk them into selling the raw compound instead of packaged stuff.

Good point. I could always ring them up, it's a small place that sells it here.

YoIaMoNwater · Jan 11, 2021

Rudeofus said:
The aim of most fogging agents is to make silver halide grains developable, but not to develop them in quantity. This is especially a concern in color processing. If you look at this list on ebi.ac.uk, there are

strong silver solvents like thioglycolate and thiosulfate

well known photographic developers like ascorbate or ferrous sulfate, which will not reduce unexposed silver halide

compounds which create extremely insoluble silver salts like Sodium Selenide, or are insoluble by themselves like metallic Tin or Pyrite

compounds known to not develop silver like Sodium Sulfite

As you can see, once you purge the list from no goes, not much remains.

PS: The phrase "Researchers often add TCEP to denature proteins during preparation of protein samples" should be interpreted as "god knows what it does to gelatin".

Well we do know what it does. It's a reducing agent and that's what you said is needed as a chemical fogging agent for reversal processing. TCEP denatures protein just as any reducing agent does, by donating electrons and breaking the sulfide bonds between cysteine residues in proteins. I don't think it'll have any negative effects on film emulsion as any other reducing agent does. Obviously it needs to be tested, but now with the 3rd lockdown in the UK I don't have access to the lab at the moment... Also I don't think that list is definite since DTT is omitted from it, meaning there are probably more reducing agents that can be used (for protein purification and probably as a fogging agent too).

Edit: Well, apparently according to researchgate (https://www.researchgate.net/post/Which_reducing_agent_do_you_prefer), TCEP doesn't reduce metal as efficiently as DTT. I guess it's not worth testing it then since it's such a expensive material and there are better alternatives. I do want to test DTT in the future though.

grainyvision · Jan 12, 2021

relistan said:
This is really good info. The product is a powder rather than a liquid, probably for the reasons you describe. It's meant to be used in one batch, which means there is every possibility that the dithionite is not evenly mixed with the carbonate. It's not powder, though, and it doesn't look like the sodium carbonate crystals that I have. It's sort of uneven, very small chunks. Possibly both carbonate and dithionite crystallized together? I don't even know if that's possible. I used a really small amount for the test on a small cut of film, maybe not enough to get the pH up high enough. I'll use some pH paper to figure out what the pH is next time.

Very interesting that phenidone is superadditive with it. I have phenidone. I have also been using paper developer as my second developer. Interesting set of possibilities there to look at down the road. Thanks!

The idea that the brown tone is from surface development makes a lot of sense! In further experiments I'll pay attention to the pH, concentration, etc now that I know it works. If I get a good result, great. If not, I have sodium thiosulfate on hand and could try a small amount of that.

To be clear, I have no idea if phenidone or metol is superadditive with it, but given how aggressive of a reducing agent it is, I could definitely imagine this being the case. It seems to not be superadditive with ascorbic acid. And be careful with a strong silver solvent as too much and you'll lose dmax silver.

Another formula that might be good to reference is Kodak FD-70, a fogging developer using dithionite. Ingredients:

* Metaborate
* 2-Thiobarbituric acid
* Sodium Dithionite

The real question here is what does the thiobarbituric acid (TBA) actually do here? It is likely impossible to source unless you're a real chemistry lab since it seems related to the sometimes abused barbiturate drug (maybe can be used as a precursor). Looking at structure and uses I'm kind of loss. It's used as dye forming agents for antihalation dyes in emulsions, but also can seemingly act as an extremely powerful anti-fogging agent, capable of rendering silver halides completely undevelopable... so why it's here is a mystery. Structure wise it has a ring like metol or hydroquinone, but seemingly is not a reducing agent? Maybe there is some reaction in solution with dithionite to form something that can act as a secondary developer?

Patent to read on it: https://patents.google.com/patent/US2636821

More reading on it's action: https://www.photrio.com/forum/threads/kodak-fogging-redeveloper-dithionite.178490/ (as well as my mistakes. Don't add to acid!)

Seemingly it is only there to prevent the silver untouched in the first developer to be undevelopable, producing clearer highlights. It can be replaced with thiosulfate according to that thread, but that actually intensifies the warmtone, likely due to rounding off of silver grains

Rudeofus · Jan 12, 2021

YoIaMoNwater said:
Well we do know what it does. It's a reducing agent and that's what you said is needed as a chemical fogging agent for reversal processing. TCEP denatures protein just as any reducing agent does, by donating electrons and breaking the sulfide bonds between cysteine residues in proteins.

Sulfite is a good reducing agent and does not denature gelatin, neither does dithionite, ascorbare or HQ. Being a reducing agent is just one essential property, but there is a lot more, and I hoped, that my issue list highlighted that. If you look at DTT, it has two thiol groups, god knows what it does to silver. Apart from that, DTT is extremely unstable at ambient temperature and needs at least a powerful sequestering agent.

Think of it like this: photographic industry used TBAB for decades, and this is about as unpleasant a compound as it gets. There must have been immense pressure to replace this with something less toxic and less nasty, yet Stannous Chloride was all they came up with. I would draw the same conclusion as Daniel Plainview: "Those areas have been drilled."

relistan · Jan 12, 2021

earlz said:
To be clear, I have no idea if phenidone or metol is superadditive with it, but given how aggressive of a reducing agent it is, I could definitely imagine this being the case. It seems to not be superadditive with ascorbic acid. And be careful with a strong silver solvent as too much and you'll lose dmax silver.

Another formula that might be good to reference is Kodak FD-70, a fogging developer using dithionite. Ingredients:
...
The real question here is what does the thiobarbituric acid (TBA) actually do here?

Thanks for the info about phenidone and metol. Re: the FD-70, I had also found that here: https://125px.com/docs/techpubs/kodak/j1-1977.pdf . I had kind of written it off because of the thiobarbituric acid. Your explanation is interesting! This actually makes me think that this ingredient might actually be able to prevent the silver staining in peroxide reversal bleach. However, I am not going to try to obtain any I wonder if there is something that acts in the same way that is not as close to a controlled substance.

YoIaMoNwater said:
Edit: Well, apparently according to researchgate (https://www.researchgate.net/post/Which_reducing_agent_do_you_prefer), TCEP doesn't reduce metal as efficiently as DTT. I guess it's not worth testing it then since it's such a expensive material and there are better alternatives. I do want to test DTT in the future though.

Give it a shot! Interested to see what you find out. It might also be interesting to see if there are any existing photographic patents that used this. Sometimes people did a lot of research but for various reasons didn't bring it to commercial market.

YoIaMoNwater · Jan 12, 2021

Rudeofus said:
Apart from that, DTT is extremely unstable at ambient temperature and needs at least a powerful sequestering agent.

That's true to a extent. It's like a lot of chemicals for reversal (KMnO4 in H2SO4 for bleaching) that needs to be used as soon as you make it. Long time storage of DTT stock power in 4C is fine. I don't know what "sequestering agent" you are talking about. I have used it numerous times in the lab for protein purification and the only problem is that it goes bad in couple of days even at 4C since it's dissolved as a solution.

relistan said:
Give it a shot! Interested to see what you find out. It might also be interesting to see if there are any existing photographic patents that used this. Sometimes people did a lot of research but for various reasons didn't bring it to commercial market.

Definitely something I will try! Just gotta see how this lockdown goes and if I can squeeze time between writing my thesis.

Lachlan Young · Jan 12, 2021

Rudeofus said:
Think of it like this: photographic industry used TBAB for decades, and this is about as unpleasant a compound as it gets. There must have been immense pressure to replace this with something less toxic and less nasty, yet Stannous Chloride was all they came up with. I would draw the same conclusion as Daniel Plainview: "Those areas have been drilled."

I think E-4's lifetime was 1965-76 or so, though obviously being kept for EIR into the 1990s, so while it might have been used for 'decades' in specific roles, it didn't last that long in anything where home users could readily get their hands on it. More perplexingly, TBAB seems to have also been in the high temperature VNF-1 colour reversal process, which lasted into the 1990s too. I suspect that @laser will know the definitive reason why VNF-1 hung on to the use of TBAB.

Mention of Boranes always reminds me of the extraordinarily dangerous Pentaborane jet fuel.

Rudeofus · Jan 12, 2021

Lachlan Young said:
so while it might have been used for 'decades' in specific roles, it didn't last that long in anything where home users could readily get their hands on it

I vaguely remember having read, that some E-6 home 3 bath kits used TBAB until the very end, but right now I have nothing to back up this claim. Either way, photographic industry had a strong incentive to avoid this compound, and Stannous Chloride is not all that great due to environmental impact. DTT would have been way too simple to overlook. These folks at Kodak were good chemists!

Lachlan Young · Jan 12, 2021

Rudeofus said:
DTT would have been way too simple to overlook. These folks at Kodak were good chemists!

Very much so - I have a distinct feeling they tried everything possible - I'm pretty sure they were either having to synthesise TBAB themselves or were the principle customer for it during the lifetime of E-4/ VNF-1.

relistan · Jan 13, 2021

I don't know guys, I think lot of things are worth a re-look. I say that because as a home user we have a very different set of constraints than a commercial process would have required. We often will put up with use-once or mix-before-use chemistry, a bit more expense, or other things that would have been the death knell for a commercial product, especially a commercial product that ran at the throughput of E4 or E6. If the chemical had some potential there are probably some patents out there. Not commercializing those might mean that they don't work at all, or it might mean that they don't work at the scale, timeframe, or price point that a commercial process used to require. And, we also have a different idea of environmental impact these days, which can change the financial incentives as well.

grainyvision · Jan 13, 2021

relistan said:
I don't know guys, I think lot of things are worth a re-look. I say that because as a home user we have a very different set of constraints than a commercial process would have required. We often will put up with use-once or mix-before-use chemistry, a bit more expense, or other things that would have been the death knell for a commercial product, especially a commercial product that ran at the throughput of E4 or E6. If the chemical had some potential there are probably some patents out there. Not commercializing those might mean that they don't work at all, or it might mean that they don't work at the scale, timeframe, or price point that a commercial process used to require. And, we also have a different idea of environmental impact these days, which can change the financial incentives as well.

On this topic, the extreme instability of dithionite and the absolute requirement that dithionite be added as a powder just before usage is likely why the commercial usage of it was relatively short

relistan · Jan 14, 2021

earlz said:
On this topic, the extreme instability of dithionite and the absolute requirement that dithionite be added as a powder just before usage is likely why the commercial usage of it was relatively short

Yeah dithionite seems to have been retained mostly in laundry or dyeing products where the normal usage is one shot and you never prepare anything before using it. I think most powder products in photography require elevated temperature to mix and so we usually don’t do that. One shot stuff tends to be solvent based. I’ll try the dithionite thing some more and see if it’s worth it.

Fogging Developer for Reversal

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