Tuesday, June 28, 2011


It seems we have some sort of "in-thing" movements in our little world of ascorbate developers.

All of a sudden there is an explosion of posts about the latest *thing*, and all of a sudden everyone agrees that we have the Solution........

For a long time noone paid much attention to fog, most people was amazed over the fact that Caffenol worked at all, and people overlooked the fact that underdeveloped images without contrast was not such a great achievement, & preferred to talk about artistic values instead.....

When ascorbic acid was introduced, and especially Reinhold's improved, more concentrated formula was introduced, we had a developer every bit as good as commercial products, and pretty son fog levels and developer fog was a theme.

KBr of potassium bromide was quickly introduced as a solution. KBr is indeed the classical restrainer & anti-foggant in photograpic developer formulae.

I wrote a little about cirtic acid as an alternative :

Citric acid is said to work as an anti-foggant solely by lowering the pH levels, a look at this article will raise some suspicion over that, my puublished calculations show very little effect on the total pH in the mix (except for low concentration CC-L), and since citric acid works very well as an anti-foggant at roughly double the weight added compared to KBr, I personally think the action from citric acid is a little more involved than some quarters think.

KBr on the other hand seems to work quite straightforward : in solution KBr is dissociated into K+ and Br- ions.  In the film emulsion we have silver HALIDES, that is silver salts from bromide, iodide and chloride (fluoride is generally not used, since it is very active). In modern times silver bromide is used more thjan the others, because it is more sensitive to light, originally silver chloride was used, and that is much less light sensitive.

Now during development silver ions, Ag+ is redusced to metallic silvers and deposited in the emulsion as silver grains (clumped together), while Br- is released into solution.

Generally speaking, if Br- is then added to the solution via KBr, the Br- ions from this addendum will tend to keep the red-ox reactin in check, and slow down development.

Lately replacing KBr with ordinary table salt has been discussed a lot.  Lately a lot has been written about IODIZED table aslt as a replacement for KBr. Pictures have been shown, thast seems to prove that this works.  And fairly unsubstantiated claims that the very very small convcentration of KI, potassioum iodide is why this seems to work.

Frankly speaking I remain somewhat sceptical about that.

First because there is relatively little AgI, solver iodide, in modern emulsions, so any addition of I- ions is likely not to work directly, like KBr have been proven to do by the whole industry.

Second because the amount of iodides is so small in table salt, compared to chlorides, that the effect thereof is likely to drown, straight KBr works directly and at a much higher concentration.

But judging from the pictures table salt seems to work, and why?

Well there are fly's in the ointment : one worker has reported a severe case of fogging or staining from the salt addition. This "salt effect" is most likely connected with the heavy dose used - at least 10 times the weight, compared to KBr, and probably has to do with the same effect as adding salt to food, a heavily salted ham changes it substantially, compared to fresh food....

That table salt seem to work, is beyond question, the trouble is WHY?

Since noone seems to have run comparative tests, I'd like to see that.

Not only comparisons to KBr and citric acid (who both works just fine), but also comparative tests between non-iodized salt and iodized salt.  I have a pretty strong hunch there would be less difference between iodozed and non-iodized table salt, thatn what is suggested.

In non-scietific terms I think that might have to do with a "halide-effect". It might be that a higher concentration of any halide-ions (Br-, I- & Cl-) in the solution works more or less the same and pushes the equilibrium towards a less active developer.

If that is the case, the massive dose of Cl- from the table salt (NaCl ---> Na+ & Cl-) is the operator, not the miniscule addendum of I-.

Since the iodized table salt available over here has 1/5 the concentration of KI in it, compared to US and EU table salts, and ince the slat additions suggested have been linked with the KI concentration in the salt, I have not tested this yet.

If I where to use the iodized table salt available, I would have to add not 10 grams, but 50 grams, personally I'm not prepared to do that, I think such a massive dose of salt would be bad for my developer, and I'm struggling with taming other effects already.

But I'd love to se a test run comparing identically exposed films, developed with Caffenol, and 4 variations, no anti-foggant, KBr, non-iodized table salt and lastly iodized table salt.
If set up for a film type known to require some anti-foggant, it would be possible to decide if table salt is a viable alternatiove to the industry standard KBr, and wether the small amount of iodide has any bearing on this at all.

At least I think its way to early to declare that iodized table salts are the way to go, KBr works 100% as advertized and table salt really has to prove itself.

Just my opinion of course YMMV.



  1. A few points to add ... Sodium Chloride is a silver halide solvent similar to Sodium Sulfite and Iodine is a restrainer. Much like instant coffee, the actual contents of table salt is not standardized and often not fully documented making it difficult to use reliably in developer formulas. Potassium Bromide and Benzotriazole both work directly and very well. While they may not be available at the grocery store you need such small quantities that a single bottle can last a lifetime.

    While I understand the "grocery store" ethic behind this I believe it is a myopic view in that the developer is only half of the development process ... there's still fixer and you can't get that from the grocery store. From a practical darkroom perspective, you still have to buy fix, or at least ammonium/sodium thiosulfate, so while you're shopping for your fixer chems you may as well get your potassium bromide at the same time (maybe get some phenidone while you're at it for some real fun).

    I also doubt some of the success stories because unless there is proper densitometry, measuring things like fog and contrast are very subjective and in many cases people see what they want to see and not what is actually there.

  2. Actual Potassium Iodide is an exceptionally powerful restrainer, it is very well known fact - it is used on the mg level, 20-40mg iirc.

    You can buy 100g KI 99% for about $17-$23 online including delivery via ebay.

    You can indeed get fixer using the "grocery store" ethic - more along the lines of supermarkets or shops like K-Mart, or BigW, that have Sulphur in the gardening section, and Sodium Sulphite (or Metabisulphite, reacted with a base to form Sulphite, though straight metabisulphite will prolly work too) heated in water produces Sodium Thiosulphate.

    Sodium Thiosulphate is also available in pool supply sections or stores as well.

    A simple scan of a developer, and 3 film tests, one with normal developer, one added KBr, one with citric acid + measured pH to verify pH level against others compared scans to see what is more dense than which.. or spot metered to calculate optical density.

    Non-iodised table salt is a weak restrainer and solvent.