Potassium Bromide

[mrred]

I am making some DS-15 and discovered I am out of Potassium Bromide. Any suggestions for a substitute?

 

[Photo Engineer]

Sodium Bromide.

 

[Rudeofus]

Before I start with substitutions for KBr: have you asked a local pharmacy whether they stock it? They won't match Formulary's pricing, but the DS-15 recipe doesn't ask for large quantities anyway.

Assuming you have access to other raw chemicals: every restrainer will do. You can use Benzotriazole, Sodium Bromide (as suggested by PE), Nitrobenzimidazole, ... be careful with strong restrainers like Iodide or Phenylmercaptotetrazole, though!

Assuming you have no extra raw chemicals: leave out the Bromide and see what happens. If you get fog, try to lower pH. Acetic Acid works nicely for this purpose, Sodium Metabisulfite may be in your chem stash somewhere, and you can add more Salicylic Acid or Ascorbic Acid (which you have anyway if you mix DS-15). Even Citric Acid or Bicarbonate will work. Start with small amounts and process tiny test clips. Incrementally add acid until you no longer get fog on your test clips.

 

[Alan Johnson]

In Caffenol there have been experiments using sodium chloride:
http://caffenol.blogspot.co.uk/search/label/table salt

 

[Gerald C Koch]

Sodium chloride is a very weak restrainer having approximately 1/1000 the power of potassium bromide. Its historic use has been with slow chloride papers such as Azo. The relative effectiveness of the three halide restrainers is iodide > bromide > chloride. As you progress down the series the next member is 1/1000 of the former.

 

[pdeeh]

some caffenol users have added iodised table salt as restrainer - its not intended to use only sodium chloride

 

[eclarke]

Don't overthink it...

 

[Rudeofus]

some caffenol users have added iodised table salt as restrainer - its not intended to use only sodium chloride

Caffenol is a single shot developer, whereas paper developers are commonly used throughout a whole printing session. The small amounts of Iodide will be absorbed by the first few sheets of paper (i.e. the silver halide grains therein). And you can't just add more table salt, because at some point you will have enough Chloride in your developer that it acts as strong solvent - see Microdol and Microdol-X.

 

[pdeeh]

I'm simply clarifying that caffenol users are using the iodised salt as restrainer rather than thinking any old table salt will do.
I'm not making any claims for efficacy or efficiency or suggesting iodised salt is any more than an emergency stopgap for film developers requiring a restrainer.

But, as so often from you, useful information Rudeofus

 

[Photo Engineer]

The bottom line is that there is no real substitute for KBr except NaBr, if you want everything else to stay the same. Yes, you need a conversion factor due to the fact that you need less NaBr, but the properties of the developer will be the same. All of the other suggestions change something.

PE

 

[mrred]

Thanks for the notes. The offending restrainer is in the mail and i opted to make it without.

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