Iodine -> Iodide

[psvensson]

I've got in my mind to try Crawley's FX-1. It calls for 5ml of a 0.001% solution of potassium iodide, which I don't have. I've tried it without the iodide, and the results are interesting - I think I'm seeing adjacency effects for the first time, for instance - but I want to try the real thing as well.

So I got some iodine tincture at the drug store. It contains 2.4% sodium iodide, which I'm guessing is functionally equivalent to the potassium salt. The problem is the 2% iodine content, which I'm guessing is not a good thing. The tincture rapidly rehalogenates developed film, for instance.

Looking around online, I found the following reaction:

2Na2S203 + I2 -> 2NaI + Na2S406

I.e. Sodium thiosulfate + iodine -> sodium iodide + sodium tetrathionate

Thiosulfate I have! I added a drop of diluted Agfa FX Universal fixer, which is basically ammonium thiosulfate + sulfite, to a drop of iodine tincture. It went colorless, which I think is a good sign.

If I'm going to do this for real I'd probably use sodium thiosulfate, so I don't get ammonium ions. I plan on adding drops of thiosulfate solution to the tincture till it's colorless, then stop, so I don't get excess thiosulfate.

What worries me is the tetrathionate. I've never heard of it. Does anyone know if it will have an effect on the development process when the iodide is diluted as far as Crawley's formula calls for?

 

[titrisol]

Iodine tincture uses iodide to allow iodine to get into solution, so it is more an iodine solution than an iodide solution... in other words it won;t work
[disregard]
1 ml 2% iodine tincture in 200ml water = 0.01% solution, then use 0.5ml of that [/disregard]

BUT $4.5 for 10g of KI from Phtographers Formulary/B&H should be worth the investment

Photographer's Formulary Potassium Iodide - 10 Grams
Mfr# 10104010G• B&H# PHPI10G

 

[psvensson]

Yeah, I know. I just don't feel like paying the shipping. Besides, this is more fun.

 

[Ian Grant]

Iodine is not Iodide, you wouldn't put chlorine on you food in place of sodium chloride.

Use FX-1b instead. In place of the iodide use 40gms/litre Sodium Sulphite (anhyd) instead. Crawley notes that he formerl called this FX-13

 

[Donald Qualls]

What worries me is the tetrathionate. I've never heard of it. Does anyone know if it will have an effect on the development process when the iodide is diluted as far as Crawley's formula calls for?

First, look here for the MSDS for sodium tetrathionate:

http://physchem.ox.ac.uk/MSDS/SO/sodium_tetrathionate_dihydrate.html

The wording "harmful" is less severe than "toxic" -- this material appears to be less hazardous than some of the developing agents we use routinely. The mechanism of hazard, based on references I found in my Google search, appears to be inteference with blood glucose transport -- large doses might induce hypoglycemia. The quantities you'll be working with probably merit no greater precaution than safety glasses and nitrile gloves, same as for developers in general and most of the chemicals you'd use for mixing developers.

Uses of tetrathionate seem to be almost exclusively related to selecting for salmonella bacteria in culture media (for food quality testing, primarily), with recent references as an anti-setting agent in near-neutral and slightly acidic wool dyes. I didn't find a single reference in a multi-page Google search to any photographic connection at all. I can only suggest trying it to see (though it's worth nothing that one reference did mention that it can be reduced to thiosulfate by a wood thiol in a strongly acidic solution -- not a likely mechanism in an alkaline developer); the quantity you'd introduce in getting a few micrograms of the iodide product is such that I'd be amazed to find any effect at all.

IMO the greater challenge, given the minute quantity of iodide called for in the formula, will be to determine the iodide content of the reacted solution with sufficient accuracy to have enough, but not too much iodide in the working solution developer. It's probably much simpler to just buy the smallest quantity of potassium iodide you can get from Photographer's Formular or Artcraft Chemical.

 

[psvensson]

Ian, I may try FX-1b, but I believe Anchell & Troop calls it a "failure" (but I don't have the book with me). That's an awful lot of sulfite for an accutance developer.

Donald, thanks for looking around! I guess it seems like the tetrathionate won't be a spoiler.

IMO the greater challenge, given the minute quantity of iodide called for in the formula, will be to determine the iodide content of the reacted solution with sufficient accuracy to have enough, but not too much iodide in the working solution developer. It's probably much simpler to just buy the smallest quantity of potassium iodide you can get from Photographer's Formular or Artcraft Chemical.

Ah yes, I hadn't thought of the factor necessary to convert 2% iodine into iodide.

Molecular weight of I2 is 253, NaI is 150. x is weight percentage of NaI in reacted solution.

2x2%/253 = x/150

The I2 is multiplied by 2 since each mole yields 2 moles of NaI

x= 2.4%

So the tincture would be a total of 2.4% NaI from reacted I2 + 2.4% native NaI= 4.8% NaI. That's the equivalent of 5.3% KI in terms of iodide ions.

 

[fred]

Lugol is a solution they daily use in clinical laboratory (for 'gram' staining in bacterio).
It's 'iodine in iodure de potassium'.

What is the position of lugol in this discussion here?

Fred

 

[Jordan]

If I were you I would just buy the iodide from the Formulary. The problem here is that your reducing agent (thiosulfate) will adversely affect the development if there is any excess present after you are done titrating the iodine out. (Like adding fixer to your developer.) Additionally I'm pretty sure that one of the reaction products of thiosulfate with halogens is elemental sulfur. This definitely has the potential to mess up your results.

 

[jim appleyard]

You could try FX-2. No Iodide/dine involved.

 

[Ryuji]

I wouldn't do any of those stuff for developer. First of all, unless you have lots of free time to waste and such a forgiving mind for endless frustration, I'd rather pay $10 for shipping to get the right stuff and be done with it. So I don't want to suggest anything else, but I would rather use iodided table salt than any of the stuff you said.

Tetrathionate is often found in poorly washed fiber prints, after several days of dry storage. This is one of several known residues that attack image silver.

Excess thiosulfate is also harmful as Jordan said.
In addition, if the outer sulfur of thiosulfate is liberated as a byproduct (sulfur -2) it's most likely fog the emulsion, or at least produce very strange result.

 

[Jordan]

Ryuji's idea of iodized table salt may work better (though NaCl has its own effects). I'm not sure what the level of iodination in table salt is. If the Formulary is too expensive for shipping you could try Artcraft or JD Photochem in Quebec depending on who's closer...

 

[gainer]

Ryuji's idea of iodized table salt may work better (though NaCl has its own effects). I'm not sure what the level of iodination in table salt is. If the Formulary is too expensive for shipping you could try Artcraft or JD Photochem in Quebec depending on who's closer...

It has been my experience that it takes a lot of NaCl to be a solvent or a restrainer for bromide emulsions. Judging from the minute amount of iodide in Crawley's formula, maybe a teaspoon of table salt would supply the iodine without undue influence on the other qualities. What's to lose by trying?

 

[jim appleyard]

I bought a box of Morton Canning Salt at the supermarket recently. It comes in a black box that says, "Nothing but salt". It was a whole $1.89

 

[Ole]

Potassium iodide is one of the most useful chemicals you can possibly have in a darkroom. Save yourself a lot of trouble and buy some. Then make up a 1% solution (1g on 100ml), take 1ml of that and dilute to 100ml to get 0.01%, dilute 1ml of that to 10 ml to get 0.001%.

 

[gainer]

I bought a box of Morton Canning Salt at the supermarket recently. It comes in a black box that says, "Nothing but salt". It was a whole $1.89

Yes, but no iodine. It's fine for simulating Microdol X, though. Add 50 to 100 grams of it to a liter of D-23.

 

[Donald Qualls]

Interesting concerns about thiosulfate in the developer and tetrathionate (in poorly washed prints) being an agent of deterioration -- but no one seems to have looked back at the original question. The OP is talking about introducing less than 100 micrograms of NaI (corrected from 50 micrograms of KI) after using the thiosulfate to remove the elemental iodine that he has already determined will bleach developed silver. Given that the iodine and NaI are in similar quantity in the original tincture, I'd expect (without balancing the reaction equation) the final diluted iodide additive solution to contain about as much (by mass) of the sodium tetrathionate as of the sodium iodide -- and I don't see introduction of a tenth of a milligram of tetrathionate per liter of working developer as being terribly likely to cause problems of any sort. Mind you, I don't see how 50 micrograms of potassium iodide could have any effect in the original FX-1, either, but Crawley liked it...

FWIW, I have used iodized table salt in a developer -- I tried adding salt to Caffenol to see if the solvent action would smooth out the grain a bit, but at the quantity I tried (as I recall, a tablespoon in eight ounces of developer, which would be close to the 100 g/L Anchell & Troop suggested was in Microdol-X), I saw neither any significant solvent action (there was no sulfite in this mixture) nor any indication of restraining action due to the little bit of iodide in the salt. However, Caffenol, being mixed by volume and working from a naturally produced coffee product, isn't the best controlled developer for this kind of experiment...

 

[psvensson]

Potassium iodide is one of the most useful chemicals you can possibly have in a darkroom. Save yourself a lot of trouble and buy some.

What do you use it for?

 

[Ryuji]

Sodium chloride has practically no restraining effect. Iodide in small quantity is said to have antirestraining effect.

Some people incorrectly conclude the fine grain effect of various developer constituents by assuming that they should work the same regardless of what developer they are added to. One recent well known argument is fine grain effect of sulfite. These agents provide significant fine grain effect when added to properly formulated low pH developer that is capable of producing fine grain, but adding them to other developers may not.

 

[psvensson]

You could try FX-2. No Iodide/dine involved.

Well, I can easily get glycin, but pinacryptol yellow is another matter.

 

[titrisol]

The iodine ticnture available in pahrmacies can be used as iodine bleach, or does it have to be diluted?

 

[psvensson]

It'll probably work diluted. I put an undiluted drop on a piece of film, and it did its thing in seconds.

Anyway, I titrated 32 ml of tincture with fix. It took 3ml to turn it clear. Then, after a few minutes, it went milky! Waiting to see if there'll be some kind of precipitate. Not encouraging, in any case.

 

[Ryuji]

I bet that's elemental sulfur precipitated by oxidation as Jordan predicted.

 

[Ole]

What do you use it for?

Potassium iodide is a restrainer. Add a little to print developers to clear up highlights, or to film developers to reduce base fog. Old paper and film can often be used by tweaking with KI, where it will give unusable results without.

You can also use it in rehalogenating bleaches to change the tones after toning.

 

[fred]

Potassium iodide is a restrainer. Add a little to print developers to clear up highlights, or to film developers to reduce base fog. Old paper and film can often be used by tweaking with KI, where it will give unusable results without.

You can also use it in rehalogenating bleaches to change the tones after toning.

Ole,

That's interesting....!
Let us know all details about it, please?

Many thanks
Fred

 

[Ole]

Ole,

That's interesting....!
Let us know all details about it, please?

Very simply stated it has the same effect as potassium bromide, only very much more. The drawback is that you need a rapid fixer to remove the residual silver iodide, whereas silver bromide is fixed adequately with sodium thiosulfate.

This same difference in solubility (binding energy) is what gives the changes in behaviour with toners.

When added to developer for restraining, it is very much stronger than bromide. And sometimes that's what you need. At other times it can be difficult to get the very low concentration needed, in which case bromide is better.