# Hypo clearing agent question



## TheForestMan

Hello!

I was just wondering how long I can keep my hypo clearing agent in a bottle?
I use the Kodak HCA and do not store it in a 2 gallon conventional plastic container (the pack is only one gallon so it is half empty). Do I need to keep it away from air contact for a better shelf life as for developers?

Also, I always hear two school of thoughts about HCA and its reusage. Does any of you have any strong argument about not reusing a HCA or have a general rule of thumb of how many time it can be reused?

Finally, do you use a working solution (diluted) or just the mix as from the instruction on the pack?

Thanks in advance!


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## unpopular

Sulfite will probobly absorb oxygen which might affect it's efficacy. You'll want to ensure that it's kept tightly closed. I have never heard of hypoclear "going bad" over time. Most chemical reactions will slow under cold storage. 

Unlike developer, you could probobly get away with mixing hypo as you go along. According to the MSDS, working Kodak Hypoclear is specified up to 5% sodium sulfite plus less than 1% metabisulfite, which is probably just a preservative or chemical stabilizer. Metabisulfite is probably a clearing agent on it's own.

To mix as you go, simply add 5g stock to every 100ml water, whcih works out to a 1:20 dilution. For a standard two roll canister, this would be, what 15g KHCA to 250ml water?

Doesn't some (ilfoclear?) have an indicator that turns blue when it's gone bad? This would suggest that if the solution is acidic, it's 'bad', though I am not sure what the tolerance would be.

(edited out mistakes RE: sodium thiosulfate and sodium sulfite)


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## Helen B

unpopular said:


> Sulfite will probobly absorb oxygen which might affect it's efficacy. You'll want to ensure that it's kept tightly closed. I have never heard of hypo "going bad" over time. Most chemical reactions will slow under cold storage.
> 
> Unlike developer, you could probobly get away with mixing hypo as you go along. According to the MSDS, working Kodak Hypoclear is specified up to 5% thiosulfate plus less than 1% metabisulfite, which is probobly just a preservative or chemical stabilizer. Metabisulfite is probobly a clearing agent on it's own.
> 
> To mix as you go, simply add 5g stock to every 100ml water, whcih works out to a 1:20 dilution. For a standard two roll canister, this would be, what 15g hypo to 250ml water?
> 
> Doesn't some (ilfoclear?) have an indicator that turns blue when it's gone bad? This would suggest that if the solution is acidic, it's 'bad', though I am not sure what the tolerance would be.



Have you got mixed up between KHCA and fixer? There is no hypo (sodium thiosulphate) in KHCA. KHCA is a buffered solution of sodium sulphite with sequestering agents. If you make your own hypo clearing agent you can just use 20 g sodium sulphite per litre of water, and discard after a session. If you re-use KHCA, don't keep the working solution for more than a week - as unpopular says the sulphite will oxidize to sulphate.

Which fixer are you using? Are you using it one-bath or two-bath? If you use a two-bath neutral rapid fixer you may not need a hypo clearing agent.


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## unpopular

OH! So the "hypo" refers to "clear" - as in, you're clearing the "hypo" (sodium sulphate)? That makes a lot more sense. So then the EDTA is to sequester (chelate) any extranious silver compounds?

The whole "clearing" thing confuses me a bit as to what is actually happening.


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## compur

Hypo Clearing Agent "Promotes removal of fixer from films and fiber-base papers to shorten  wash times and make washing at lower wash-water temperatures practical" (Kodak)


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## Helen B

Yeah... It's a bad name. Ilford call their version 'Washaid' and Heico call theirs 'Perma-Wash'. It is intended to speed the removal of hypo (which is both sodium thiosulphate and, because of that, a generic old-time name for fixer) after fixing (fix - short water wash - wash aid - final water wash). Here's the abstract of a paper by the two Kodak guys who patented KHCA.

There's was also 'hypo eliminator' which really did eliminate all hypo - this has become unpopular after research showed that a very small amount of residual fixer was beneficial. Ilford, however, call their Washaid a hypo eliminator, even though it may not be a hypo eliminator in the old sense. Confusing, huh?

Best,
Helen


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## unpopular

Sorry for the confusion guys. I often make this mistake. I've edited my post to reflect this correction.


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