Farmers shelf life unmixed

[Toffle]

This is probably covered in a thread somewhere, but the answer is not popping off the page for me...

I know that once you combine Farmer's solutions A and B, they must be used immediately. What is the benchmark for unmixed solutions? (and... if I'm cooking my own chemistry, which is more likely to need replacement?) I never use that much of it or that often, so I can't recall what the solutions looked like when I first mixed them, but I noticed last night that solution A was a very cheerful yellow in colour.

Last question... Replenish or replace? I know Farmer's is ridiculously inexpensive, but it is one of those chems that sit half used in my cupboard. I'd rather use it than dispose of it.

Cheers,

 

[Ian Grant]

Don't cook with it, both parts attack metal pots & pans

More seriously the two parts keep for years particularly if mixed in a more concentrated form, you'd save nothing attempting to replenish and it would be inefficient.

Ian

 

[Gerald C Koch]

The mixed solution cannot be replenished since the sodium thiosulfate quickly destroys the potassium ferricyanide. Replenish implies that there is still some activity left to replenish.

 

[Toffle]

The mixed solution cannot be replenished since the sodium thiosulfate quickly destroys the potassium ferricyanide. Replenish implies that there is still some activity left to replenish.

That is a given, but how about the solutions in their separate containers? My concern is having to dispose of chemicals that have lost their potency through sitting too long on the shelf, though as Ian says they will keep for years if stored separately.

cheers,

 

[Mike Wilde]

The thiosulfate (clear) stock could sulfur out just like conventional fixers. The KFerri will stay orange forever in a cool dark place stored in a capped glass container. If it looses it's needed valency if turns to a green (actually less toxic as waste, I understand).

I usually wing it with Farmers, by pouring the about right amount of KFerri into a small amount of fixer, or, if I am doing full print reduction (ie overexposure oops fixes) FB prints, I just mix a dilute bath of K Ferri, and pull the print in fresh from the fixer bath and agitate regularly for the first minute or so.

 

[Toffle]

The thiosulfate (clear) stock could sulfur out just like conventional fixers. The KFerri will stay orange forever in a cool dark place stored in a capped glass container. If it looses it's needed valency if turns to a green (actually less toxic as waste, I understand).

I usually wing it with Farmers, by pouring the about right amount of KFerri into a small amount of fixer, or, if I am doing full print reduction (ie overexposure oops fixes) FB prints, I just mix a dilute bath of K Ferri, and pull the print in fresh from the fixer bath and agitate regularly for the first minute or so.

Thanks, Mike.