Hypo Wash Crystals

[Pieter12]

I noticed with the last gallon jug of hypo wash concentrate I had that quite a few large crystals had formed at the bottom after a while, about when I was getting to the last quart or so. Is this common? Does it affect the remaining concentrate? I have been careful that none of the crystals made it to the working solution, but it did bother me. I looked at the label and there is nothing there that would indicate special attention or a life-span for an opened/resealed container. I may try to purchase quart bottles in the future if that might help. Also, I don't keep working strength hypo wash for more than a few days, as I have seen it gets some sort of scummy growth.

 

[fgorga]

My (educated) guess is that the crystals are sodium sulfite, the compound present in highest concentration in most hypo clearing solutions. The presence of crystals means that there will be less of that component (whatever it is) in the stock solution and therefore less in the working solution. Is this a problem? Possibly, if you usually push the capacity of this solution to near its limit for neutralizing the hypo.

There are two possible causes for the formation of crystals upon long term storage of a stock solution. Evaporation of some of the water because the bottle was not capped tightly. This could cause the concentration of one (or more) of the components to rise above its saturation point. Alternately, prolonged storage at too low a temperature can cause things to drop out of solution. Most compounds become less soluble as the temperature drops.

You could try gently warming the bottle (with the cap on loosely) and agitating the contents of the bottle to see if you can get the crystals back in solution. If that doesn't work I would probably continue to use the solution but would err on the side of caution with regard to capacity. For example (with random numbers), if you usually treat a dozen 8x10 with 1 L of working solution before discarding it, I would maybe only treat 6-8 prints instead, just to be sure that you don't use up the active ingredients.

 

[Pieter12]

Thanks. I just found that crystals forming is to be expected after prolonged storage of an opened container--it was buried at the end of the datasheet. But the option of dividing up the concentrate into smaller, sealed containers seems feasible until I start buying it in quart bottles instead of gallons.

 

[Rudeofus]

Regardless of what these crystals are, their contents are probably not missed much in the working solution. HCA is not a balanced product like developer or fixer, it is some ions which facilitate ion exchange between emulsion/paper and the wash water (thiosulfate out, sulfite/carbonate/... in). Therefore I would continue using the HCA concentrate until it is used. Chances are, that the crystals will dissolve in the working solution.

I wonder, whether the crystals are Sodium Bicarbonate, which is surprisingly poorly soluble, and which would form, if too much aerial Carbon Dioxide is dissolved. This could be easily checked by adding some lye to the concentrate - if the crystals dissolve, the Sodium Bicarbonate has been converted back into the better soluble Sodium Carbonate. In any case the concentrate should be still usable.

 

[focus_on_infinity]

Is there any advantage to mixing it up in quantity? I've been mixing 12.5g/500ml at a time, and tossing it after a handful of rolls.

 

[MattKing]

Is there any advantage to mixing it up in quantity? I've been mixing 12.5g/500ml at a time, and tossing it after a handful of rolls.

It doesn't keep, so no.
HCA is the only darkroom chemical that I scoop small portions out of the bag and then add water each time I need some. The relative proportions of the constituent ingredients aren't particularly important.